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It is important to increase the production rate of oil and gas as the usage of them is increasing day by day. To increase the production rate of oil and gas, design of an efficient centrifugal pump impeller plays very important role. Due to the usual submergible pump, there might be the chances for failure and it is so complex when the pump is failed. So an alternative method such as artificial lift is necessary on behalf of submergible pumps for different flow rates. In the present study, 3D simulation of impeller and its stationary flow of centrifugal pump casing are analyzed using CFD. Pressure head and efficiency of the pump for different flow rates are analyzed as well as the data from pump manufacturers are taken and have good satisfactory agreement. Finally, the structural analysis of single impeller blade is carried out by changing different materials. These data are very useful to design the pumps in manufacturing industries.

Cementing is one of the important steps in well construction. This chapter shows how to calculate the amount of additives required for mixing the different types of cement slurries. These additives provide properties of fluid loss, setting time and rate (i.e., acceleration or retardation), and reducing the friction to prevent high pump pressures on deep high-density casing jobs. Calculations to provide the proper placement for support of the casing and to ensure that the casing is anchored to prevent casing shoe movement after the cement is pumped are detailed. Other important cementing operations include pumping and placing open hole plugs and balancing the pressures, so the plug will not “U-Tube” when the pipe is removed from the plug. Finally, it is important to determine if the casing will move up (called “hydraulicing”) the hole as the different density cement slurries are pumped in place.

Актуальность исследования обусловлена необходимостью предотвратить введение в прифильтровую зону объема породы с большей однородностью и большего размера по сравнению с крупной фракцией пластового песка - попытка добиться улучшения фильтрационных свойств прифильтровой зоны, т. е. снижения [zeta]2фк и [zeta]2n. Конструкция гравийной набивки одновременно должна исключать вынос частиц пласта в скважину. Решение этой проблемы позволит улучшить работу фильтрации пластовой жидкости из пласта в скважину и сократить затраты на дополнительное применение методов интенсификации притока пластовой жидкости к скважине. Цель: разработать методику, позволяющую при выборе конструкции фильтра, одновременно с возможностью обеспечения им надежной гидравлической связи в системе пласт-фильтр, предотвращать вынос песка в скважину. Объекты. Для предотвращения поступления песка из пласта и удержания гравия на забое скважины при создании гравийных набивок применяют щелевые, проволочные, кольцевые, титановые, металлокерамические и другие фильтры. Эти фильтры, установленные в интервале перфорации обсадной колонны без образования гравийной наружной кольцевой набивки (а именно таким образом в большинстве скважин устанавливаются фильтры на месторождениях России), очень часто забиваются пластовым песком, что приводит к снижению продуктивности скважин. Если для задержания песка используются щелевые фильтры, то эффективность их применения зависит от соответствия размера щелей гранулометрическому составу выносимого песка. Фильтры с ракушечной набивкой более эффективны, но также не всегда отвечают поставленной цели, поскольку прочность и качество ракушечника, закачиваемого в прискважинную часть пласта, довольно низкие. Кроме того, примененные на промыслах проволочные фильтры не имеют фиксации каждого витка, в результате чего при механическом повреждении одного из витков происходит срыв всей намотки. Методы. При применении предложенной методики полученные результаты экспериментальных работ по оценке способов снижения выноса песка из несцементированных неоднородных пластов показывают, что применение фильтров в обсаженном стволе требует создания гравийной набивки в кольцевом зазоре между фильтром и колонной, в перфорированном канале и за обсадной колонной. Причем размер гравия должен быть выбран таким, чтобы исключить перемешивание гравийной обсыпки с пластовым песком за счет миграции и интрузии песка, т. е. D/d=4-5. Снижения производительности скважин можно в этом случае избежать путем увеличения размера и количества перфорационных отверстий. Следует отметить, что предотвращение выноса песка означает, что при оптимальном установившемся режиме работы скважины фильтр удерживает частицы скелета пласта, но пропускает мелкодисперсные и глинистые частицы. В период запуска скважины картина несколько иная - пропускается и часть скелетообразующих частиц до того момента, пока на фильтрующей оболочке не образуется естественный фильтр из отсортированных крупных фракций. Результаты. Частицы, которые составляют структуру породы, не должны выносится из пласта за счет применения фильтра. Практически это означает, что фильтр должен не пропускать 75-85 % (по весу) более крупных фракций песка. Для сохранения общей устойчивости скелета пласта можно допустить вынос мелких частиц не более 15-25 % (во весу). The relevance of the study is caused by the need to prevent the introduction of a volume of rock with greater homogeneity and larger size into the near-filter zone compared to the coarse fraction of formation sand - an attempt to improve the filtration properties of the near-filter zone, i. e. decrease in [zeta]2фк and [zeta]2n. The design of the gravel pack should simultaneously exclude the removal of formation particles into the well. The solution to this problem will improve the work of filtration of formation fluid from the formation into the well and reduce the cost of additional application of methods for stimulating the inflow of formation fluid to the well. Purpose: to develop a methodology that allows, when choosing a filter design, simultaneously with the ability to provide them with a reliable hydraulic connection in the reservoir-filter system, preventing sand removal into the well. Objects. To prevent the flow of sand from the formation and retain gravel at the bottom of the well, when creating gravel packs, slot, wire, ring, titanium, cermet and other filters are used. These screens, installed in the casing perforation interval without the formation of gravel outer annular packing (and this is how screens are installed in most wells in Russian fields), are very often clogged with formation sand, which leads to a decrease in well productivity. If slot filters are used to retain sand, then the effectiveness of their application depends on the correspondence of the slot size to the granulometric composition of the sand being removed. Filters with shell packing are more effective, but they also do not always meet the set goal, since the strength and quality of shell rock pumped into the near-wellbore part of the formation are rather low. In addition, wire filters used in the fields do not have fixation of each turn, as a result of which, if one of the turns is mechanically damaged, the entire winding breaks down. Methods. When applying the proposed technique, the results of experimental work on evaluating ways to reduce sand production from unconsolidated heterogeneous formations show that the use of filters in a cased hole requires the creation of gravel packing in the annular gap between the filter and the string, in the perforated channel and behind the casing. Moreover, the size of the gravel should be chosen so as to exclude the mixing of the gravel packing with the formation sand due to the migration and intrusion of sand, i.e. D/d=4-5. A decrease in well productivity can in this case be avoided by increasing the size and number of perforations. It should be noted that sand avoidance means that under optimal steady state well operation, the filter retains formation backbone particles, but allows fines and clay particles to pass through. During the well start-up, the picture is somewhat different - part of the skeletal particles is also passed through until a natural filter of sorted coarse fractions is formed on the filtering casing. Results. The particles that make up the rock structure should not be carried out of the formation by applying a filter. In practice, this means that the filter should not pass 75-85 % (by weight) of the larger sand fractions. To maintain the overall stability of the formation skeleton, it is possible to allow the removal of small particles not more than 15-25 % (in weight).

In view of the geological characteristics of high pressure in salt-gypsum formation of deep wells in Tarim Piedmont structure, high-density oil-based drilling fluids are widely used, which makes it difficult for subsequent cementing work. In order to solve the technical difficulties of cementing high-density oil-based drilling fluid and salt-gypsum formation in KS well, which is a key exploration well in this area, through analysis of cementing technical problems, combined with salt-gypsum formation cementing and deep well ultra-deep well cementing technology, targeted measures before casing running, optimization of flushing aggravated isolating fluid and aggravating agent are carried out. In addition, relevant technical measures are put forward based on the optimization of cement slurry additives, the design of slurry formulation pipe string structure and the optimization of cementing technology. A set of flushing aggravating isolating fluid was prepared by introducing small particle size, concentrated superfine aggravating agent and hematite powder with relatively large particle size, and a set of high-density cement slurry with good comprehensive performance was obtained by optimizing cement slurry additives and introducing super high-density aggravating agent GM-1. In order to ensure the safety of cementing, the adaptability test of cement slurry formula was carried out, focusing on the adaptability test of cement slurry temperature and density: when the temperature changes + 5 °C the density increases + 0.03 g/cm3, the thickening time of the system changes less than 44 min, the system has good stability, and the anti-channeling performance of cement slurry SPN is less than 3, which has good anti-channeling function and meets the construction requirements, At the same time, the compatibility experiments of different proportions and different media and the simulated intermittent cementing experiments are added to meet the requirements. Field application of KS well shows that the technology can meet the cementing requirement of oil-based drilling fluid in Piedmont area.

Shear deformation often occurs during multistage fracturing of shale gas worldwide, increasing the operation cost of gas well completion and lowering the well’s productivity; strike-slip fault slippage is thought to be a crucial underlying factor. This paper presents a detailed analysis of the influence of strike-slip fault slippage on casing inner diameter and establishes a technique for predicting casing inner diameter after fault slippage. Numerical simulation models were developed to simulate the process of fault slippage and calculate changes in the inner diameters of the casing, considering different engineering and geological conditions. The influential factors, including the fault strike angle, slip distance, radius-thickness ratio, and mechanical properties of the formation, were analyzed in engineering practice; the simulation results were shown to be consistent. Four methods, including adjusting the wellbore trajectory of shale gas horizontal wells, avoiding perforation at the formation interface, decreasing the fracturing parameters including the fracturing pressure, discharge capacity, volume of injecting fracturing fluid, and prediction of casing inner diameter after casing shear deformation, were proposed and verified through engineering application and theoretical calculation, respectively.

One of the largest trap intrusion provinces, Siberian traps, is located in the East-Siberian Platform in Russia. A trap intrusion zone usually has abnormally low reservoir pressures and natural fractures. Consequently, trap drilling is associated with fluid losses that can be catastrophic. The section of trap intrusion is a part of a Ø 174 mm production casing section of the Srednebotuobinskoe field. The basic well design of this section also includes the Osinsky horizon, which features an abnormally high reservoir pressure zone. The latter creates incompatible with drilling conditions environment due to the presence of catastrophic loss zones in traps. Time spent on drilling a trap intrusion zone accounts for up to 30 % of the total well drilling time. The abovementioned geological issues in directional wells become the key topic in solving it. The method to resolve this issue is an integrated approach employing all the technologies and technical facilities aimed at finding a technological solution. First of all, in order to optimize the well construction cycles and reduce the complications, all the wells were classified in three categories as per the type of behavior in trap intrusion. This allowed to work out multi-level activities, that depended on severity of losses and non-operational time spent on drilling through this section. An alternative well design was developed and trialed on several wells, which showed positive results on decreasing non-productive timing. The main concept of this design was significantly different from the basic well design that was used in the past on the Srednebotuobinskoe field. The main difference was isolation of traps from the high pressure Osinsky horizon lower section with a Ø 245 mm casing string, which allowed safe splitting of two incompatible drilling zones. The economic effect of this solution allowed saving of up to 10.4 days or 15 % of the construction time in the wells of first category. These results were reviewed at the Technical Committee of the Company and agreed to implement the alternative well design on first category wells on the Srednebotuobinskoe field. In addition, for the rest of well categories the Drilling Team has produced and successfully implemented the preventative measures that allowed drilling through traps with lost circulation material. It is worth to mention that this method assumed a by-passing mud-cleaning system on the rig to allow building up a solid phase thus stemming the losses while drilling. For all the categories of the wells the Drilling team has selected and trialed different types and designs of drilling bits that would allow drilling hard rock such as dolerite section in traps with minimal number of runs. For the last five years the Drilling team together with the bit producing companies have designed a new type of PDC cutters that would allow to enhance durability as well as improve drilling speed both in dolerite formations and in overlying formations in the Production casing section. The Drilling team has also managed to reduce the number of trips associated with early bit wear decreasing them from five to two runs and create an experimental basis for drilling the entire section of the production casing in one run. From 2019 team continue looking for further solutions that would allow to improve bottomhole assembly elements balancing between durability and drilling rate in different types of formations above and below traps. A range of proposed technological solutions significantly reduced the impact on the well construction performance by preventing and reducing the downhole losses events in the section of trap intrusion on the Srednebotuobinskoe field.

The perforating technique is one of the well completion methods and a final stage that helps connect reservoir formation to wellbore during hydrocarbon production. The present work aimed to determine the effect of the perforated casing completion on the pressure gradient and perforation skin factor in the vertical near-wellbore region. This work presented a novel experimental approach for studying the effect of perforation parameters on hydrocarbon production by creating a prototype representing the near-wellbore region. The study conducted extensive laboratory testing to create two prototype artificial samples for a cylindrical near-wellbore region, open hole, and perforated casing sample. An experimental test was carried out using a geotechnical radial flow setup to measure the differential pressure in the two samples; the single-phase (water) was radially injected into the core sample within the same flow boundary conditions. Numerical simulation and statistical analysis were used to expand the investigation of the effect of the dimensions and distribution of perforations on the perforation skin factor and the pressure gradient in the cylindrical near-wellbore region. The results showed a clear view of the effect of the perforations’ parameters on the pressure gradient in the vertical near-wellbore region. In addition, two novel correlations were produced from statistical analysis that simplified the estimation of the perforation skin factor in the perforated casing completion. This study will help to clarify and understand the effect of perforation parameters on well productivity.

With the exploration of marine oil fields in deep and ultra-deepwater regions, the need for studying different methods of well construction has increased. Nowadays, the technique of laying conductive casing by jetting is the most widely used for the starting phase of a well in such conditions. In this scenario, in early layers, where the marine soil is in contact with seawater, this material can present itself as a fine mud, characterizing a cohesive non-drained soil, with low shear strength, being considered a material with viscoplastic behavior. Thus, as such, using fluid rheology to analyze it may represent a valid option; being possible to classify it as a Herschel-Bulkley fluid. The use of computational modeling and numerical simulation represent an alternative to understand the behavior of soil during jetting. In this context, this work focuses on developing a computational modeling of the jetting of marine soil, based on the soil fluid dynamics approach, using computational fluid dynamics (CFD - Computational Fluid Dynamics) software SIMULIA XFLOW, version 2020. This work aims to investigate the deformation in the seabed in response to an incident vertical jet using different drilling fluids, also modeled as viscoplastic materials. Drilling fluids suitable for jetting and a fluid with a higher specific mass were considered. For the proposed modeling of the soil and drilling fluids considered, the main parameters used were the yield point, consistency index, behavior index, and the boundary viscosity. The latter was necessary to implement the modified Herschel-Bulkley model used by the software. Results show that the excavated cavity presented a similar behavior for the drilling fluids suitable for jetting, indicating that the rheology of the drilling fluid does not interfere with the deformation of the soil. However, a significant influence on the profile of the excavated cavity was observed when implementing the drilling fluid of higher specific mass in the jetting, which deformed the soil at greater depths.

Generally, geothermal fields in Indonesia are situated in the mountains, forests, and remote area. The surface area, access, environment, license, and permit are limited, so that from a permitted well pad many wells are designed directionally to reach the reservoir. Directional drilling in geothermal wells is challenging due to hard volcanic rocks, the presence of vugs or cavern, and high temperatures leading to massive lost circulation, drilling break, and the difficulty to turn and control the direction stably during drilling. These cause a critical condition reducing the wellbore quality: high Dogleg Severity (DLS), tight hole, and stuck pipe occurrence. Besides, this leads to higher stress and strain experienced by the casing or liner and causes yield strength reduction and failure. Thus, it is essential that the directional drilling design and operation, particularly trajectory, be optimized. This research summarized methods to evaluate the actual drilling operation and wellbore condition of wells in Dieng Field. The result is useful to identify the critical conditions caused by drilling and formation problems setting the maximum load limitations of the design and subsequent operation. It is recommended that buckling analysis, full-scale testing, and several design and operation scenarios be conducted prior to the drilling operation.

During cementing operation with oil-based drilling fluids, the casing and well wall are in the "oil wet" environment, and the cement slurry cannot achieve good cementation with the second interface, which seriously affects the cementation quality of the cementing interface. Therefore, it is very important to select a flushing fluid with good performance and high flushing efficiency for cementing operation with an oil-based drilling fluid. An integrated measurement system of interface parameters and a rotating liquid interface tension tester is selected in the room. A set of evaluation methods of wetting reversal is developed to evaluate the wetting reversal ability of type A and type-B flushing fluids on site to optimize the reasonable type and concentration of the flushing fluid. The experimental results show that under the same concentration, the surface tension and interfacial tension of type A flushing solution are lower than those of type-B; that is, the hydrophilic effect of type A flushing solution is better than that of type-B. The wettability reduction of type A is better than that of type-B. The wetting reversal ability of type A flushing solution with a surfactant concentration of 30% is better than that of type-B. The evaluation methods include surface tension, interface tension, dewetting ability, and oil washing ability of the flushing fluid, and the evaluation of the wetting reversal ability is carried out on the basis of the sandstone, sheet metal (steel for three open casings on site), and slide glass (as a reference). Then, according to the optimal concentration of the flushing fluid, a mixing experiment of the two kinds of flushing fluids is carried out to evaluate the ability of wetting reversal, and compared with the experimental results of A and B, the reasonable flushing fluid formula is finally selected. A proper analysis of the adaptability of the evaluation method of the flushing fluid is conducive to the reliable evaluation of the performance of the flushing fluid and the enhancement of the operator's ability to grasp the cementing quality. To guide the field practice has a very important practical significance, but it also has a guiding role for the development of new pre-liquid products.

In the petroleum industry, packers refer to the components/products which are used to isolate one section in a formation from others, or to isolate the outer section of a production tubing from the inner section, which may be a casing or a liner or the wellbore itself. Mechanical packers are installed through some form of tubing movement. Permanent packers are low in cost and provide better seal. Retrievable packers have lower sealing capability but are re-usable after repair, and therefore expensive. More innovative packers made of swellable elastomers are rather new. These elastomers swell when they come in contact with different types of fluids (mostly water and oil). Like a casing, these new packers are lowered to the desired depth and allowed to swell before production or injection operations begin. Various studies have been published about the swelling and mechanical response of these elastomers. However, many questions remain about the sealing performance of swell packers, and their effectiveness in actual wellbores of rough and random profiles. This paper describes the design and development of an experimental unit for performance testing of a mix of inert and swelling elastomer seals under realistic well conditions. Actual swell packers and petroleum tubulars are housed in a concrete block that replicates open-hole and cased-hole wells through layers of varying roughness. This is a one-of-its-kind unit providing full-scale demonstration about the working of swell packers against outer casing or rock formation in a wellbore. It is also a complete testing apparatus to investigate the behavior of swell packers made of fast-swell and medium-swell elastomers, and how they seal off irregular boreholes. This work can provide basic understanding and visual corroboration to petroleum engineers and students, swelling elastomer application developers, and academic and research personnel.

The integrity of perforated liners is crucial in geothermal production wells and this should be well designed according to correct standards. The available geothermal standards, such as the New Zealand Standard, NZS2403:2015, provides a general but less detailed discussion of geothermal perforated liner system design considerations. This research aimed to improve the limitations of NZS2403:2015 by calculating and evaluating the dynamic loads of perforated liner during four phases: borehole drilling and liner installation, flow testing, stand-alone production, and production during the injection operation. The data from production well HCE29 and injection well HCE29A, Dieng Field, Indonesia, were used in this research. In every phase, perforated liner yield strength changed, and load mechanisms varied between 1.3-2.7 and 1.6–4.6 times of the actual liner burst and collapse strength, respectively, and these lead to perforated liner failure and its lifetime reduction. The calculation results, combined with the significant production decline and production casing failure, indicated the perforated liner failure. The results also showed when it was mandatory to revise operation at later phases and to conduct appropriate maintenance according to actual perforated liner condition. Furthermore, this study can be used as a basis of future wells design and operation related to perforated liner.

Cuttings accumulation in horizontal drilling of a shale gas well is one of the main reasons for high drilling torque and drag and serious backing pressure and consequently influencing the rate of penetration (ROP), so inhibiting the generation of a cuttings bed and keeping the hole clean is an important prerequisite to ensure the smooth and safe drilling of horizontal section. In order to improve the hole cleaning efficiency of horizontal sections, this paper studied the decay laws of helical flow induced by helix angles and rotation speed of a newly developed cuttings bed remover with V-shaped blades for horizontal wells and their influences on the resuspension distribution of cuttings particles by virtue of the CFD numerical simulation method and Euler–Euler binary-fluid model, combined with the theory of particle dynamics. Then, the parameters such as blade rotation speed and blade helix angle were optimized. And the following research results were obtained. First, with the increase of the rotation speed, cuttings deposit at the bottom of the annulus deflects to a certain degree. And the higher the rotation speed, the more obvious the deflection. Second, annulus pressure drop loss increases with the increase of the helix angle. And this phenomenon is more obvious when the helix angle is larger. Third, the field test results in Well Changning H25-7 of the southern Sichuan Basin show that after the application of the newly developed cuttings bed remover for horizontal wells, the drilling friction is decreased by 33 %, the tripping is smooth without sticking. And in the process of its application, no complex downhole accident happened. Obviously, it provides good hole cleaning to ensure the safe and smooth implementation of the later casing running operation. In conclusion, this newly developed cuttings bed remover can satisfy the demand of cutting bed cleaning and drilling cost reduction and efficiency improvement of horizontal wells, so it is worth popularizing and applying. What's more, it provides guidance and reference for the design of similar cuttings bed removers.

The AOV-1 well is a development well that is planned to be drilled in the “ANTARIS” Field. Based on the data obtained from the nearest well of “AOV-1” well, a casing design will be carried out, therefore it is necessary to select casing specifications. So that it can meet the requirements technically and economically. Casing design planning is the preparation of file collected from drilling prognosis, and daily drilling report so that it can be used for calculation of pressure parameters, knowing stratigraphy, lithology, subsurface data, availability of casing stock in warehouse, and planning technical calculations for casing design operations such as d-exponent calculation to determine pore pressure, pressure calculation (formation pressure, overburden pressure, fracture pressure), calculation of the load received by casing (burst load, burst load design, collapse design), determination of casing setting depth, casing grade selection for casing design, calculation of biaxial stress correction of tension and compression stress, calculation of safety factor, and finally, calculation of economics from planning casing design. 7 ” casing program grade K-55, 20 PPF, BTC at a depth of 0 - 1968.5 ft TVD with safety factor Ni = 3.83 each; Nc = 2.19; Nj = 13.54, only 1 section is performed. casing program 9/8 " Casing program with grade K-55, 36 PPF, BTC at a depth of 0 - 820 ft. TVD with a safety factor of each Ni = 9.91; Nc = 4.83; Nj = 30.06, only 1 section is performed. 13 3/8 " casing program with grade K-55, 54.5 PPF, BTC at a depth of 0 - 250 ft. TVD with a safety factor of each Ni = 63.77; Nc = 22.99; Nj = 226.73, only done 1. The total cost for casing planning is $ 57,689 or around Rp. 816,876,240 of the budget provided, which is $ 65,000 or around Rp. 920,400,000.

The paper considers the process of hydrate-paraffin deposits formation in oil wells. Due to the research with the author's specially designed laboratory equipment – an experimental installation containing a technological unit and an information-measuring system, the most favorable pressure-temperature conditions of hydrate formation in a wide range of pressure (0.1–120 MPa) and temperature (from –20 to +80 °C) were determined. The experimental results made it possible to determine the conditions required for hydrate deposits and iron (Fe) oxides in the range of temperature from –15 to +60 °C and pressure from 0 to 60 MPa. These results are confirmed by thermodynamic calculations of the oil-gas-hydrate phase equilibria in the annulus of the well. Data processing was performed using the methods of correlation, dispersion and regression analysis, which allowed comparing the processes of hydrates and iron (Fe) oxides formation in the annulus of oil wells. The results of the study can be used to prevent and eliminate hydrate-paraffin plugs in the downhole equipment of oil wells, and also to determine the operation mode of the well for long-term operation of the downhole equipment without complications, accidents and stops for repair works, which reduces downtime.

Multistaged temporary plugging fracturing in horizontal wells is an emerging technology to promote uniform fracture propagation in tight reservoirs by injecting ball sealers to plug higher-flux perforations. The seating mechanism and transportation of ball sealers remain poorly understood. In this paper, the sensitivities of the ball sealer density, casing injection rate and perforation angle to the seating behaviors are studied. In a vertical wellbore section, a ball sealer accelerates very fast at the beginning of the dropping and reaches a stable state within a few seconds. The terminal velocity of a non-buoyant ball is greater than the fluid velocity, while the terminal velocity of a buoyant ball is less than the fluid velocity. In the horizontal wellbore section, the terminal velocity of a non-buoyant or buoyant ball is less than the fracturing fluid flowing velocity. The ball sealer density is a more critical parameter than the casing injection rate when a ball sealer diverts to a perforation hole. The casing injection rate is a more critical parameter than the ball sealer density when a ball sealer seats on a perforation hole. A buoyant ball sealer associated with a high injection rate of fracturing fluid is highly recommended to improve the seating efficiency.

The conditions for applying the method of drilling boreholes with simultaneous casing are considered. The most used tool designs, their advantages and disadvantages are shown. Present-day requirements for this tool are indicated. A new design is presented, which allows further drilling through the casing pipe of maximum possible diameter, simulation results are given. The operation of the device is described and a diagram of its use is presented.

In this study, an integrated approach of advanced spectral noise and high-precision temperature logging with production logging tool was used for the understanding of leak detection, fluid cross-flow, flow below spinner threshold, packer failure, fluid channeling in patchy and bad cement bond behind the casing, flow quantification in complex SSD completion, production detection and quantification in recirculation intervals in deviated wells. Various case studies from Southern and Northern Iraqi oil fields have been presented in this paper.

The extrusion load on casing in ultra-deep well is uncertain, which limits the application of safety factor method. Therefore, the evaluation method of collapsing safety and reliability on casing during drilling in ultra-deep wells is put forward. Based on the extrusion load model in ultra-deep well considering the diversity of strength parameters of casing and the integrity of formation-cement sheath-casing system, the uncertainty distribution functions of collapse strength and extrusion load on casing are derived by introducing probability and statistics theory. Then, the theory of "stress-strength interference" is applied to obtain the reliability R, confidence interval and reliability-safety factor nR of casing. Taking multiple ultra-deep wells in the Kuqa block of the Tarim Oilfield as an example, the collapse safety and reliability analysis on casing is carried out. Several conclusions are made based on the oilfield statistics. The traditional safety factor is greater than the reliability-safety factor. The surface casing and the production casing are both safer than the technical casing. More accurate original data can narrow the confidence interval width of nR and reduce the collapse risk of technical casing. The change in reliability is consistent with the change of the reliability-safety factor. For technical casing, when R is greater than 0.50 and 0.92, nR is greater than 1.0 and 1.1 respectively. For production casing, when R is greater than 0.98, nR is greater than 1.1. For each type of casing, affected by the uncertainty of the extrusion load on casing, when the extrusion load exceeds a certain value (but this value is less than the casing strength), the reliability begins to decrease. The larger the standard deviation of extrusion load is, the more obvious the influence on reliability change will be. Compared with the traditional design safety factor, the change of the anti-collapse safety degree of the casing can be more intuitively displayed by the reliability, which could provide an important supplement for the selection of traditional design safety factor during drilling operations.

Long-term zonal isolation is crucial for the development of fossil hydrogen energy, while efficient filter cake removal is the basis for successful zonal isolation. However, enhanced filter cake removal usually relies on adding chemicals into preflush fluid, which are potential pollutants to the environment. In this study, engineering parameter optimization is used to realize enhanced filter cake removal. Firstly, filter cake removal was identified as multiple-phase fluid flow, and a new three-fluid numerical model was established accordingly. The effects of five engineering parameters on the removal efficiency were simulated and the results showed that borehole enlargement and casing eccentricity reduced removal efficiency. The critical borehole deviation angle and casing rotation speed for optimal removal efficiency were 45° and 40 rpm, respectively, while the removal efficiency monotonously increased with flushing velocity. After all engineering parameters were optimized, the maximum removal efficiency was as high as 89.34%, which was comparable to that achieved by using potentially polluting chemicals. The borehole enlargement rate was identified as the most sensitive parameter, followed by casing eccentricity, flushing velocity, borehole deviation angle, and casing rotation speed subsequently. Two empirical models to predict removal efficiency were developed for convenient field application. Briefly, the complex removal behaviors of the filter cake are better understood for reducing the risks of failed zonal isolation and avoiding chemical overuse, which potentially contributes to the cleaner and more environment-friendly production of fossil hydrogen energy.

With increasing depth of exploration and process boreholes (at small drilling diameters), the probability of deviation of the borehole path from design trajectory increases many times; i. e. zenith curvature and azimuth deviation of the borehole path occur. Therefore, developing methods for keeping vertical path of the borehole when drilling deeper horizons of ore bodies is a very topical issue. The paper presents the results of developing a new bottom-hole assembly for drilling boreholes in soft rocks using screw casing centralizers, which provide good stabilizing and centering effects to mitigate horizontal departure of the hole axis from the design direction and minimize vertical curvature of the hole path (zenith angle) while maintaining sufficient drill string flexibility. The developed technical solutions provide simplicity of design and ability to adapt to wide range of mining, geological and technological drilling conditions. The feasibility of manufacturing the centralizers by own efforts and the technological feasibility of quick and easy connecting the centralizer with other elements of the bottom-hole assembly have been substantiated. The manufacture efficiency is proved by the use of inexpensive and wear-resistant materials in the centralizer armouring, for which tungsten-cobalt or titanium-cobalt hard-alloy inserts were used. In addition, prevailing volume of borehole drilling in soft rocks allowed using replaceable centering elements, as well as their repair and restoration to increase their service life. The manufactured centralizer has a low production cost due to the design simplicity and the use of inexpensive wearresistant material and will compete in the market of drilling tools and technical devices for drill string stabilization. The economic effect from the introduction of the self-produced centralizers amounted to more than 170,000 tenge per a borehole.

The control of surge and swab pressure is an important guarantee to maintain the safety, cost savings, and high efficiency of well control operation, so the calculation of surge and swab pressure is very important. If the drilling speed is not properly handled, it may cause a blowout, surge and swab pressure losses, and wellbore fluid losses during the drilling process. To avoid the occurrence of complicated downhole conditions in the drilling process, the surge and swab pressure should be calculated with high accuracy. In this paper, we have considered the effect of casing coupling in the calculations of the surge and swab pressure. A case study shows that when the impact of coupling is taken into consideration, the calculated surge and swab pressure value is higher than that ignoring the coupling. Therefore, neglecting the impact of coupling could cause a significant error when calculating the surge and swab pressure.

SummaryInterpretation of sonic data acquired by a logging-while-drilling (LWD) tool or wireline tool in cased holes is complicated by the presence of drillpipe or casing because those steel pipes can act as a strong waveguide. Traditional solutions, which rely on using a frequency bandpass filter or waveform arrival-time separation to filter out the unwanted pipe mode, often fail when formation and pipe signals coexist in the same frequency band or arrival-time range. We hence developed a physics-driven machine-learning-based method to overcome the challenge. In this method, two synthetic databases are generated from a general root-finding mode-search routine on the basis of two assumed models: One is defined as a cemented cased hole for a wireline scenario, and the other is defined as a steel pipe immersed in a fluid-filled borehole for the logging-while-drilling scenario. The synthetic databases are used to train neural network models, which are first used to perform global sensitivity analysis on all relevant model parameters so that the influence of each parameter on the dipole dispersion data can be well understood. A least-squares inversion scheme using the trained model was developed and tested on synthetic cases. The scheme showed good results, and a reasonable uncertainty estimate was made for each parameter. We then extended the application of the trained model to develop a method for automated labeling and extraction of the dipole flexural dispersion mode from other disturbances. The method combines the clustering technique with the neural-network-model-based inversion and an adaptive filter. Testing on field data demonstrates that the new method is superior to traditional methods because it introduces a mechanism from which unwanted pipe mode can be physically filtered out.This novel physics-driven machine-learning-based method improved the interpretation of sonic dipole dispersion data to cope with the challenge brought by the existence of steel pipes. Unlike data-driven machine learning methods, it can provide global service with just one-time offline training. Compared with traditional methods, the new method is more accurate and reliable because the processing is confined by physical laws. This method is less dependent on input parameters; hence, a fully automated solution could be achieved.

A high-performance technology for constructing cased wells is proposed. Essence of the technology is the advance insertion of the casing pipe into the sedimentary rock mass and the cyclical-flow transportation of the soil rock portions using the compressed air pressure supplied to the open bottomhole end of the pipe through a separate line. Results of mathematical modeling for the process of impact insertion of a hollow pipe into a soil mass in horizontal and vertical settings are considered. Modeling of the technology is implemented by the finite element method in the ANSYS Mechanical software. Parameters of the pipe insertion in the sedimentary rock mass are determined - value of the cleaning step and the impact energy required to insert the pipe at a given depth. Calculations were performed for pipes with a diameter from 325 to 730 mm. Insertion coefficient is introduced, which characterizes the resistance of rocks to destruction during the dynamic penetration of the casing pipe in one impact blow of the pneumatic hammer. An overview of the prospects for the application of the proposed technology in geological exploration, when conducting horizontal wells of a small cross-section using a trenchless method of construction and borehole methods of mining, is presented. A variant of using the technology for determining the strength properties of rocks is proposed. Some features of the technology application at industrial facilities of the construction and mining industry are considered: for trenchless laying of underground utilities and for installing starting conductors when constructing degassing wells from the surface in coal deposits. Results of a technical and economic assessment of the proposed technology efficiency when installing starting conductors in sedimentary rocks at mining allotments of coal mines are presented.

Aiming at the problems of microfracture development in hard brittle shale gas layer in Fuling block, Chongqing, such as collapse of borehole wall and the existence of permeability loss of microfracture during drilling, and serious pollution of drilling environment with oil-based drilling fluid, a water-based drilling fluid system for anti-collapse and anti-leakage was studied. A water-based drilling fluid system with anti-collapse and anti-leakage was formed by introducing functional treatment agents, such as polypolysaccharide MEG, polymer emulsion film forming wall cementing agent LFGB, polyamine inhibitor LCFA and deformable particle plugging agent BXLZ, into the conventional water-based drilling fluid. After rolling at 130°C for 16 h, the system has good rheological properties, low filtration loss, good inhibition, lubrication and plugging properties. It has good plugging properties for 0.12 mm, 0.24 mm, 0.38 mm micro-cracks and 400 mD and 800 mD sand plates. The system was successfully tested on site in August 2019 in Fuling Reef Block, showing good rheological properties, solid wall plugging, and strong ability to seal and inhibit fracture expansion. There was no block falling in the drilling process, and the tripping, casing running and well cementing operations were all smooth, which provided a new technical idea and scheme for environmental protection and green drilling in Fuling shale gas exploitation.

In shaft construction, conducting shaft drilling and pregrouting simultaneously is expected to speed up the sinking rate and save the cost. Reasonable determination of the spatial locations of the drilled shaft and grouting holes and proper defining of the start time of each construction work are the crucial techniques. To smoothly execute the simultaneous operations, the bedrock to be grouted is divided into two sections. The upper bedrock is injected first using straight grouting holes to act as a tight cover to protect shaft drilling. Then, the lower formations are grouted using S-shaped grouting holes, which are performed simultaneously with shaft drilling. The construction time of simultaneous operations of pregrouting for the lower bedrock using S-shaped holes and shaft drilling is the saved time. The main technical challenges include the stability of grouting holes and safety of shaft walls, as well as the disposal of the contaminative waste drilling mud. The stability of grouting holes which might affect by the shaft drilling-induced ground vibration could be evaluated according to the penetration of ground vibration caused by TBM tunnelling. If the grouting hole is in the range of ground vibration, protective measures including casing and ground improvement should be utilized to ensure the stability of grouting holes. The stability of unlined walls of the drilled shaft caused by the increased groundwater pressure can be achieved by a tight cover between the drilled shaft and pregrouting holes. The thickness of the cover is actually the length of the straight holes. The cover should have sufficient thickness and impermeability, which can considerably reduce or even completely stop the increased groundwater pressure in vicinity of the drilled shaft. The thickness and permeability of the cover could be determined using Maag’s solution for penetration of grouts in porous media. On the other hand, the waste drilling mud with proper modifications can be reutilized to prepare clay-cement-like grouts, which could provide an eco-friendly and cheap solution to harmlessly treat the huge volume of waste drilling mud. The properties of waste drilling mud and behaviors of grouts prepared using the waste mud should be experimentally investigated before reutilization, owing to uncertainties of geology in various cases. The construction time using the simultaneous operation method is just about 60% of that of the traditional excavation method, and the low value of measured residual water inflow shows the reliability of reusing the waste drilling mud as grouting materials. The proposed method could virtually improve the shaft sinking rate and save the construction cost. The principles developed for these technical challenges have been proved to be applicable in practices, which are believed to strongly support the applicability of this new method in other cases.

Effect of depletion rate on wellbore stability due to production of oil from hydrocarbon-bearing reservoirs is important and can result in a reduction of the reservoir pore pressure. A reduction in the reservoir pressure, in turn, results in a change in the stresses acting within the reservoir. If these changes are not well analyzed and applied in future calculations, we may be unsuccessful in some cases such as drilling infill wells or extended wells, forecast of sand production and optimum flow rate, preventing of casing collapse, etc. Therefore, knowing the stresses around the well at every stage of production is fundamental to the next calculations. In this paper, we recognized these changes in near-wellbore stresses using data from logging (image log, dipole sonic, full set log, mud log), production data, information from kick, blow out, loss etc. and determined it using Techlog software and theoretical calculations. Three wells of two huge oilfields of SW Iran were investigated after depletion or production for long years. In each well, state of stresses were calculated in cases of safe drilling mud weight using log data and theoretical equations. At the end effect of depletion rate on wellbore stability was investigated in these three wells.

Plug-and-perf multi-stage hydraulic fracturing completions in unconventional reservoirs rely upon complete hydraulic isolation from the previous stage to ensure effective treatment of the active stage. Failure to isolate stages can be a result of partially set plugs, plugs set in wellbore debris or deformed casing, unqualified pressure/temperature rating of plugs, etc. This paper presents a case study with field examples where unexpected casing erosion occurred at the setting depths of the dissolvable frac plugs during hydraulic fracturing and subsequently resulted in loss of inter-stage isolation. A 12-well, 4-layer, cube pilot was designed with permanent fiber optic cable to collect Distributed Acoustic Sensing (DAS), Distributed Temperature Sensing (DTS) and Distributed Strain Sensing (DSS) data as well as downhole pressure gauges for development insight and future completion optimization. The cable was mapped, and oriented perforation techniques placed entry holes opposite the fiber along the wellbore, and no loss of communication was observed during perforating operations. However, fiber optic signal was lost during hydraulic fracturing operations on one or more stages in all four instrumented horizontal wells. Real-time DAS/DTS analysis indicated the fiber breaks were consistently occurring below the lowermost perforation cluster in the stage, at or very near the frac plug setting depth. Step-down tests were also performed and showed significantly enlarged effective treating area. Based on this observation, post-frac downhole imaging tools were deployed to investigate potential casing and perforation erosion. Downhole imaging data clearly showed the casing was severely eroded at several locations. Additional interrogation of the damage with respect to plug design components indicated that damage always occurred near the plug sealing element. By integrating the analysis of DAS/DTS, step-down tests and ultrasonic imaging, it was determined that the frac plug bypass is creating a loss of casing integrity at the plug set location. Casing integrity loss resulted in multiple fiber optic cable breaks and lowered the ability to evenly distribute slurry into treatment clusters. Fiber optic data analysis showed that 50% of the larger OD dissolvable frac plugs had bypass compared to 100% bypass for the smaller OD high-expansion dissolvable plugs. To establish key patterns and identify critical variables that influence stimulation effectiveness, it is important to obtain several different diagnostic datasets and perform an integrated evaluation using all available information. This study also reinforces the need for operators and manufacturers to work together to design and qualify frac plugs against realistic downhole conditions, particularly in areas with potential casing deformation issues. Industry innovation is required to enable fracturing operations to continue through deformed casing. This includes advancing equipment, tools, and techniques for plug-and-perf and other multi-stage completion methods.

In several design calculations including the development of programs to optimize production, engineers and scientists require accurate prediction of temperature drop due to flow in oil wells. The purpose of this research is to create mathematical models to predict the effect of oil mass flow rate on temperature distribution in oil wells. A numerical mathematical model is developed to study the parameters affecting the dynamic and static temperature profiles in oil wells in production and shutting operation. The temperature distribution of the oil from the reservoir to the surface and the temperature distribution in the wall tubing of the oil well and casing, cement sheaths, and surrounding formation is studied. The natural flow of oil wells in Alwahat area located 70 Kilometres south of Marada area east of Libya in the Zaggut field called (6Q1-59) is taken as a study case. In production case, different mass flow rates in winter and summer seasons are studied. The temperature profile in the horizontal direction is estimated at different depths. The Results show that the surface temperature of crude oil increases with the rise in mass flow rate.

The Winkie Drill is an agile, commercially available rock coring system. The U.S. Ice Drilling Program has modified a Winkie Drill for subglacial rock and ice/rock interface coring, as well as drilling and coring access holes through ice. The original gasoline engine was replaced with an electric motor though the two-speed gear reducer and Unipress hand feed system were maintained. Using standard aluminum AW34 drill rod (for 33.5 mm diameter core), the system has a depth capability of 120 m. The drill uses forward fluid circulation in a closed loop system. The drilling fluid is Isopar K, selected for favorable properties in polar environment. When firn or snow is present at the drill site, casing with an inflatable packer can be deployed to contain the drill fluid. The Winkie Drill will operate from sea level to high altitudes and operation results in minimal environmental impact. The drill can be easily and quickly assembled and disassembled in the field by two people. All components can be transported by Twin Otter or helicopter to the field site.

Casing, with its two main elements: casing setting depth and casing design, is one of well barrier elements playing a significant role for geothermal well integrity. All of the internal and external loads experienced by the casing from its installation into the well until the end phase of well, called plug and abandonment, have to be calculated precisely. Moreover, the casing must be able to withstand the geothermal environment: high-temperature, high-strength rock, highly-fractured formation, corrosive fluid, and under-saturated pressure. Therefore, the casing specification can be properly determined based on the technical and economic considerations to achieve a high quality of well integrity and endurance starting from drilling and completion, production, maintenance (well intervention, and workover), conversion into an injection well or vice-versa, and plug and abandon (P&A). This research study discussed the production well HCE29 in Dieng Field, Indonesia, characterized by a water-dominated geothermal system with temperature of up to 330 °C and pressure of up to 19.4 MPa. After the well was drilled and completed, the casing failure was identified. This study consisted of analysis and re-calculation of this well at the phases of drilling, completion, production, and maintenance to improve the casing setting depth and design method. The results show that the casing failure occurred in this well. In addition, this study improved the Philippines’ method used for re-calculation of casing setting depth and the casing design evaluation method.

Geothermal energy has been in rich in both onshore and offshore conditions. Air can be used as working fluid at offshore platforms for geothermal energy development. However, existing models cannot...

The article considers causes of complications and accidents occurring while drilling in the Jurassic deposits in the intervals of Bazhenov, Georgievski and Abalakski formations at the fields of West Siberia. It proposes technical and technological solutions for their trouble-free drilling and production casing RIH. The measures developed provide for preventing instability of wellbore in the interlayers of clay and mudstone, removal of drill cuttings in the wells with zenith angles exceeding 50 degrees and in extended reach wells, avoiding tight hole and stuck pipe problems, ensuring RIH to the bottom hole and good quality of cementing jobs.

Based on the analyzing of industrial materials has been established that lot of gas wells characterized of inter-string flows and could not been effective be on stream. The article has been shown, that main base of this problem is poor quality well cementing, first off all the interval of reservoir horizon. After researched of information of well cementing has been ascertained that first eight hour of the curing of cement is attended by drop of the hydrostatic pressure. It becomes the main reason of oil and gas inflow. The drop of cement stone sealing properties during long time maintenance is result of poor cement stone resistance to thermocorrosion in the subsurface conditions. This is the reason that new cementing slurry recipe should be prepared. This recipes should be provides a differentiated rate of strength gain during the time of waiting the cement in conditions with high technological properties for long time maintenance. One of the most dangerous process during well construction is oil and gas inflow or inter-string flows in time of wait-on-cement time. This time is characterized special conditions of cement stone, because it represents as permeable matrix with hydration products, and with porous full by water. It is the best conditions for the flow of fluid throw pores. It can be the reason of suffusion channeling. In order to prevent for oil and gas inflow the article has been invited the achieve optimal distribution the pressure. For the realized this purpose can been used cementing process with two cement slurry batch with different setting up time. In practice of cementing of casing with length of section capital string, which shut off the gas more than 400 m, use differentiation the wait-on-cement time the portion of cementing slurry with length of cement column. In result start of time wait-on-cement in the bottom portion should be less for 2-3 hour than top portion. Keywords: water-mixture ratio, rheological properties, wellbore pressure, component of cement mortar column, cement mortars, cement mortar hardening, rate of strength gain, strength of cement ring References: Bandur R. V., Luzhanytsya O. V., Mykhaylenko S. H. [and other]. 2005. The problem of selection of the formulation of cementing solutions for a specified downhole conditions. Issues of development of the gas industry of Ukraine: Collection of scientific works UkrSGRI. Kharkiv. P. 135-137. (in Ukrainian) Bonett A., Delyus P., Shuger L 1998 Gas Migration - Looking Into the Problem. Oil and gas review. Spring. Р.18-23. (in Russian) Bulatov A.I. 1991. Grouting materials and well cementing technology. Moscow: Nedra. P. 336. (in Russian) Gorsky V.F. 2006. Cementing materials and solutions. Chernivtsi: 524 p. (in Ukrainian) Danyushevskiy V. S., Aliyev R. M., Tolstykh. I. F. 1987. Grouting Materials Reference Moscow: Nedra. P. 373. (in Russian) Luzhanitsya O. V., Mikhaylenko S. G., Kotskulich Y. S., Lazarenko O. G. 1997. To the problem of tightness of the annulus in the early stages of the grout. Exploration and development of oil and gas fields. Series: Drilling of oil and gas wells. - Ivano-Frankivsk: IFDTUNG. №34. Р. 88-91. (in Ukrainian) Instructions for determining the conditions of use of gas wells with the presence of intercolumn pressure drilled on the shelf of the Black and Azov Seas: Approved. Derzhnaftogazprom of Ukraine, OJSC «Ukrainian Oil and Gas Institute», NPC «Chornomornaftogaz» 1997; Validity is not set. Derzhnaftogazprom of Ukraine. 11 p. (in Ukrainian) Kuksov A.K. 1985. Improving the quality of well cementing. Oil industry. №9. P. 25-27. (in Russian) Orlovsky V.M. 2015. Grouting materials that expand during hardening. Monograph. Poltava. 129 p. (in Ukrainian) Levayn D. K., Tomas E. I., Bezner H.P., Tolpa D. K. 1980. Prevention of gas migration in the annulus of a cemented well. Oil, gas and petrochemicals abroad. N 10. P. 8-12. (in Russian) Technological regulations on cementing of casings in wells at the fields of JSC «Ukrnafta» for 1996- Derzhkomnaftogaz OJSC UkrNGI. 1995. Kyiv. 36 p. (in Ukrainian)

Casing corrosion during CO2 injection or storage results in significant economic loss and increased production risks. Therefore, in this paper, a corroded casing risk assessment model based on analytic hierarchy process and fuzzy comprehensive evaluation is established to identify potential risks in time. First, the corrosion rate and residual strength characteristics are analyzed through corrosion tests and numerical simulations, respectively, to determine the risk factors that may lead to an accident. Then, an index system for corroded casing risk evaluation is established based on six important factors: temperature, CO2 partial pressure, flow velocity, corrosion radius, corrosion depth and wellhead pressure. Subsequently, the index weights are calculated via the analytic hierarchy process. Finally, the risk level of corroded casing is obtained via the fuzzy comprehensive evaluation. The corroded casing risk assessment model has been verified by a case well, which shows that the model is valuable and feasible. It provides an effective decision-making method for the risk evaluation of corroded casing in CO2 injection well, which is conductive to improve the wellbore operation efficiency.

Rotating Magnet Ranging System (RMRS) is one of the core guiding technologies for shale gas extraction, and its magnetic measurement data will inevitably be affected by the downhole magnetic objects in the target magnetic field. The casing and drill pipe, which are apt to be magnetized by the magnetic sub, are major influencing factors of the measurement results. In order to study the influence comprehensively, a dual horizontal well RMRS drilling model is established. Based on static magnetic dipole theory, the magnetic field distribution equation of the low‐rotational magnetic sub is deduced and characterized. Firstly, the casing and drill pipe were segmented into ring, layer, and block volume elements. Then according to the dynamic magnetic dipole field distribution equation, the magnetic field strength of the magnetic source at the volume element (equivalent magnetic dipole) and the sensor was calculated, as well as the magnetic strength of independent magnetization field and superposition magnetization field of casing and drill pipe at the sensor position. Finally, the effectiveness of the numerical method results was verified by outdoor experiments, and the shielding effect of the static magnetic shielding on the external magnetic field of casing was preliminarily analyzed. The research results indicate that the magnetic sub has a strong magnetization effect on the casing and drill pipe. The magnetization field of the casing is about 2.39 times stronger than that of the drill pipe, and they will seriously affect the sensor measurement data. When the well spacing is small, the magnetization field waveform will be distorted. With the increase of the well spacing d, the waveform gradually changes sinusoidally, the fluctuation period of the magnetization field also gradually becomes twice (d > 1.5 m) that of the magnetic source, and the peak value of the magnetization field decreases exponentially. A preliminary analysis of the magnetic shielding of casing revealed that the magnetic shielding would cause great attenuation to the strength of the magnetic source. The numerical simulation proposed in this paper provides a theoretical basis for the error analysis of RMRS, which is of great significance for measurement correction and accuracy improvement.

Casing damage caused by sand production in unconsolidated sandstone reservoirs often results in oil wells unable to produce normally. However, due to the complex mechanism of sheath damage caused by sand production, there is no more mature technology for predicting the risk of casing damage in advance. Data-driven method can better integrate various factors and use a large amount of historical data to solve complex classification prediction problems. In this paper, XGBoost and LightGBM algorithms are used to establish casing damage prediction models, and 13 model application experiments are carried out to optimize the set of casing damage factors. These two algorithms are used to calculate the feature importance of each factor and determine the final set of factors. The evaluation results of five key metrics show that both prediction models show good performance, and the prediction accuracy is 0.99 for the XGBoost model and 0.94 for the LightGBM model. Applying the established prediction model can determine reasonable range of the maximum daily liquid production of a single layer (Qlmax) to reduce the probability of casing damage. In addition, at certain Qlmax, increasing the perforation density can significantly reduce the probability of casing damage. Therefore, increasing the perforation density can achieve high production without causing casing damage.

Summary Conventional well plug and abandonment (P&A) can sever and remove the tubing to access casing or leave it in situ when it does not interfere with providing a seal over an indefinite time frame. This paper assesses the viability of pushing rather than pulling severed production tubing to gain casing access. The P&A decision to push, pull, or leave the tubing in situ depends on confirming existing seals and then placing suitable sealants, such as cement, to keep the risks of future well leakages as low as reasonably practicable (ALARP). Pushing or compacting tubing into the liquid space of a well could be used with smaller rigless units, which cannot hoist the production tubing, but can use production intervention or decommissioning logistics with coiled tubing or wireline cutting and severance. Associated pumps could then drive an inflatable piston to compact split and severed tubing into a lower liquid space to access casing for logging and P&A plugging. Rigless tools and methods have provided dramatic cost savings where casing access was not needed, and thus the present study investigates the viability of accessing casing by means of pushing or compacting tubing to extend rigless P&A use and savings. The viability of pushing and compacting North Sea sizes and grades were confirmed in real-scale physical-compaction simulations of production-tubing joints pulled from offshore wells. Independent small-scale physical simulations and numerical modeling then confirmed that the real-scale results were predictable and repeatable to demonstrate an ability to design and provide a window or gap in a production-tubing string for use by other P&A methods.

Pulsed neutron-neutron (PNN) logging is based on emitting neutrons into the near-wellbore zone and computing the neutron count decay due to scattering and capturing. The main application of this logging tool is to determine the current oil saturation and to detect channeling in perforated and non-perforated intervals behind the casing. Correct interpretation of the results obtained from PNN logging enables engineers to predict new perforation intervals in depleted reservoirs. This study examines the application of PNN logging in a well located in one of Iranian oil reservoirs. The interpretation procedure is described step by step. The principle of the PNN logging and the specifications of the tool are discussed and the applications of PNN logging in evaluation of oil saturation, identification of water flooded zones and prediction of potential perforating zones are described. Channeling is also investigated between all layers, good and poor oil zones are characterized based on the calculated oil saturations and new perforation intervals are suggested with the aim to boost oil production from the reservoir. The results of this study show that zones 1 to 5 having low oil saturations, are interpreted as depleted oil zones. Zones 6 to 8 are interpreted as good oil zones having high potential to produce oil. Zone 9 is interpreted as a water zone.

In the Sichuan Basin, the drilling of complex deep and ultradeep wells is restricted by the casing sequence. Multiple pressure systems are usually encountered in the same open hole section, and narrow safety density window is observed in vertical strata. The application of managed pressure drilling (MPD) technique which is often used in well drilling ensures the safe and efficient drilling, but it also brings about great challenges to the small-gap liner cementing at the lower part. Therefore, it is of great practical significance to research a cementing technology that can not only satisfy the quality requirement of small gap liner cementing, but also ensure the safe cementing in the strata with narrow safety density window. In this paper, a cementing technology based on precise managed pressure balancing method was proposed by referring to the successful application of MPD technique. According to the cementing design, the hydrostatic column pressure of annulus fluid is under-balanced (slightly lower than the formation pore pressure), and then a precise managed pressure drilling device is adopted to produce back pressure through wellhead restriction or apply wellhead compensation pressure, so that the balanced pore pressure can be reached in the process of cementing via the wellhead pressure and the flow friction of fluid in the annulus. After the cementing is completed, a certain compensation pressure is applied to the annulus continuously to prevent annulus channeling during waiting on cement caused by insufficient static pressure and slurry weight loss. After this technology was applied to an ultradeep exploration well in the Sichuan Basin, the qualification rate of borehole cementing quality reached 97%, and the well sections with good cementing quality accounted for 76%. In conclusion, this technology needs no additional equipment, and only by virtue of the MPD equipment, it can achieve safe cementing construction and cementing quality improvement under high displacement efficiency.