Search

The static metallic joints’ sealing performance is deeply impacted by the plastic deformation and the interfacial separation of the contact surfaces with self-affine roughness. The yield hardening effect, unavoidable at the contact interface, is of vital importance to the plastic deformation and the distribution of the interfacial separation. However, most of the previous research ignores the effect of the yield hardening, assuming that the contact surfaces are elastic-perfectly plastic. To address the problem, a novel analytic model for investigating the sealing performance under the effect of yield hardening has been developed in this paper. Utilizing the measured data of contact surfaces as input, the corresponding leakage rates are calculated. Besides, the contact stress distribution as well as the real contact area at the interface are also discussed. The sealing experiments are carried out accordingly, verifying that the proposed model owns the ability to predict the leakage rate under the effect of yield hardening.

Conventional geo-steering approach use raw logging measurements to define wellbore positioning within the reservoir while drilling. The geo-steering specialist usually compares real-time logs to modelled logs (GR/Density/Neutron/Resistivity) and the geological model is then adjusted to make real-time decisions to deliver the well objectives. This conventional method is applicable to most reservoir conditions. However, it may be insufficient or inappropriate in heterogeneous reservoirs or wells with complex geological settings, potentially resulting in wells being sub-optimally placed and reducing the value of reservoir sections in terms of productivity. This paper aims to showcase a Petrophysics-based Geo-steering approach to maximize the value of reservoir sections. Geo-steering aims to place the well trajectory in the lithology with optimum storage capacity, flow capacity and hydrocarbon saturation. The method of log-to-log comparison is popular for its simplicity and speed of use in real-time but is not enough for certain scenarios. For example, the real-time log response can be very different from modelled log response in the presence of gas or very light oil, irrespective of petrophysical properties (porosity/permeability) being similar. Moreover, real-time Sw estimation would be required in addition to porosity to minimize the risk of drilling a producer into water bearing intervals. In fact, the comparison between petrophysical parameters is more appropriate to heterogeneous reservoirs or wells with complicated geology. This approach requires good co-ordination between geologist, petrophysicist and geo-steering specialist. Prior to drilling, the petrophysical model from offset wells should be defined and used to derive porosity, permeability and saturation. While drilling, the petrophysical properties are then interpreted in real-time and based on the comparison between modelled and real-time petrophysical properties, decisions are to be made with respect to the well objectives. An example with strong gas effect in a carbonate reservoir from Abu Dhabi is presented to demonstrate this novel approach. Real-time density/neutron does not have good correlation with modelled density /neutron due to gas effect. Such poor correlation can be attributed to proximity to a Gas Oil Contact (GOC) and dynamic invasion, complicating the real-time geo-steering. However, real-time total porosity from log analysis correlates very well with modelled total porosity, providing confidence in wellbore positioning and allowing the geologist and the geo-steering specialist to make the correct real-time decision to place the well in the optimum stratigraphic position in order to meet the well objectives. Only conventional logs are utilized in this case, but if real-time NMR and resistivity image interpretation are available, it will provide additional information in term of permeability, secondary porosity and irreducible water saturation to aid efficient geo-steering.

Carbonates heterogeneity is a continuous challenge for subsurface experts. The case in hand illustrates the advantage of data integration between Logging While Drilling (LWD) including Nuclear Magnetic Resonance (NMR), High-resolution image and Wireline (WL) formation testing and fluid sampling. The formation evaluation integration analysis results are used for characterizing the rock quality across multiple reservoir zones and to determine the optimum zones to be drilled horizontally and completed using the inflow control device (ICD) completion. Appraisal and improvement of the lateral drainage area of the reservoir are the main objective of the field development strategy, by drilling pilot holes to evaluate Cretaceous carbonate layers then targeting the optimum zone for lateral side-track based on the provided data. Therefore, the plan has initiated by deploying the advanced LWD including the Gamma Ray, propagation Resistivity, Neutron, Density and Micro-Resistivity imaging along with NMR to acquire all the needed data for formation evaluation and reservoir characterization. The formation pressure testing and sampling device has been deployed using Wireline (WL) for the comprehensive evaluation of subsurface resources. In this study, the reservoir petrophysical properties including total, effective porosity, permeability, movable fluid and bound water volume provided from NMR played an important role for the reservoir characterization and enhancement of the final formation evaluation results, based on the NMR results the formation testing / sampling points were decided. The Micro-Resistivity image revealed various types of geological features such as the conductive, enhanced, resistive fractures and different bedding plane in addition to different geological textures were interpreted along the well trajectory and was used to fine tune the formation testing and fluid sampling zones. The fluid mobility analysis from formation testing is used to calibrate the NMR permeability index along with the comparison with core data, also, the fluid characterization and sampling result are integrated with the rest of the data to formulate better reservoir understanding. The final integrated results from all the data and analysis used to identify the highest potential zones, therefore the side-track lateral drain was planned and geosteered based on the data integration results from the pilot hole. By extending the pilot hole understanding to the lateral section, the lateral section completed successfully across the optimum zones. This paper provides insight into the integration of the Open Hole logging data from Logging While Drilling and Wireline to eliminate the uncertainty of the reservoir characterization and Formation Evaluation analysis to sustain and increase the oil production.

Wireline (WL) measurement emerged a long time before the logging while drilling (LWD) technology which created generations of petrophysicists with different school of thoughts. With the dramatic increase in the adoption rate of the advanced LWD technologies, highlighting the logging environment effects and revisiting our understanding of the formation responses logged under different borehole conditions are more critical than ever. Hundreds of LWD datasets from various environments have been reviewed to identify its effects on data quality and responses from bottom-hole-assembly (BHA) design, driving mechanism, tool eccentricity, well angle, mud properties, differential invasion, borehole condition, formation fluid properties, and drilling fluids interactions. Some of these effects co-occur on many occasions, complicating the log response. Examples and demonstrations of our understanding and interpretation of these phenomena are discussed in the study. Looking to the reservoir in the relatively fresh state, a few minutes after drilling with an understanding of the logging environment provides a unique opportunity to obtain precise formation evaluation and insight into reservoir behavior when combined with different time laps acquisitions. This work is a continuation and addition to (Parmanand et al., 2018) which was extended to include more environmental factors in different oil fields and reservoirs with more advanced LWD technologies. This work summarizes the long cumulative experience of interpreting LWD measurements, shares the main observations related to LWD responses and serves as a ready reference to identify measurement artifacts from actual formation responses. It is helpful as a reference guidebook for log analysts, geologists, geo-steering engineers, and others.

The high stability and tightness of modern aviation hydraulic pipelines require them to have a very low leakage rate under variable pressure environments. Once the leakage of the hydraulic pipeline is likely to cause an irreversible air disaster. Flaring straight pipe joint is one of the most widely used in aircraft hydraulic pipelines. The establishment of the simulation model is an effective method to accurately predict the annular gap leakage of the pipe joint. The ring gap of the pipe joint is located inside the threaded sleeve, which cannot be directly observed. The existing leakage prediction methods usually only focus on the microscopic interface contact and ignore the leakage prediction of real complex structures. Therefore, this article is based on ideas, semi-physical simulation through experimental data calibration tightening torque and annular gap width and the mathematical relationship between void ratio, and then established the flaring type straight pipe joint circular aperture leakage prediction simulation model, the ability to different tightening torque and hydraulic pressure conditions for predicting the pipe joint leakage rate, finally, the simulation experiments have been carried out to verify prediction model, The validity of this method is proved.

Horizontal well drilling contribute to a dramatic increase of shale gas production in unconventional reservoirs. However, the drilling is also risky and challenging with different types of drilling problems often encountered including stuck pipes, inflows, losses and pack-offs, etc. To reduce shale-gas development costs, shale gas operators are faced with finding effective solutions to minimize drilling risks and improve drilling efficiency. A holistic workflow, which can be divided into three steps: pre-drilled modelling and assessment, real-time monitoring, and post-drilled validation, is proposed. Based on the pre-drilled geomechanical modeling, mud weights, mud formulations and casing setting depths are optimized to ensure wellbore stability during the drilling process. Real-time operations involve monitoring drilling parameters and cavings characteristics (shape and volume), and providing updated recommendations for field drilling engineers to mitigate and reduce borehole instability related problems. During the post-drilled stage, the updated geomechanical model will be used for optimizing the drilling designs of upcoming wells. With geomechanics as foundation, a systematic workflow was developed to provide integrated solutions by using multiple technologies and services to reduce serious wellbore instability caused by abnormal formation pressures, wellbore collapse and other complex drilling problems. The implementation of the systematic and holistic workflow has proven to be extremely successful in supporting the drilling of shale gas wells in China. The integrated approach, which was applied in a Changning shale gas block in Sichuan Basin for the first time in March 2019, recorded an improvement in ROP by 111.2% and a reduction in mud losses by 89.9% compared with an offset well without the risk mitigation strategy applied in the same pad. The geomechanics-based approach provides a convenient and effective means to assist field engineers in mud weight optimization, drilling risk assessments, and horizontal well drilling performance evaluation. The approach can also be extended to reduce potential drilling risks and improve wellbore stability, all of which contributes to reducing drilling costs and optimizing subsequent massive hydraulic fracturing jobs.

The shale revolution has extended the life cycle of the oil and gas industry, promoted the growth of global oil and gas reserves and production, and changed the energy's strategic pattern of various countries. At present, the national shale-gas demonstration area of PetroChina Changning and Weiyuan is in the stage of large-scale production. Horizontal well and hydraulic fracturing are two key technology that have proven to provide an effective way to economically develop medium to high maturity shale gas resources. However, due to geological complexity of the shale-gas demonstration area, and the lack of robust analysis and research on overpressure mechanism and wellbore instability characteristics, drilling events such as stuck pipes, lost circulations and inflows occurred frequently during horizontal well drilling. These non-productive events greatly restricts the wellbore construction cycle time and the production of shale gas reservoir. A comprehensive geomechanical study was carried out from which the three pressure profiles required for drilling, i.e., pore pressure, collapse pressure and fracture gradient, are established. The study also clarified the spatial distribution of overpressure across the field. The improved pore pressure and geomechanical understanding of the field provides the necessary inputs for an integrated, multi-disciplinary approach carried out during pre-drilled analyses, real-time monitoring and post-drilled evaluation to manage the stability of horizontal wells. The safe mud weight window derived from geomechanics provides the basis for mud weight and mud formulation designs that can be continuously optimized to improve wellbore stability and reduce drilling risks. The integrated approach has been applied for 4 horizontal wells in Weiyuan's shale gas field. One of the wells, Wei202-H34-3, has the horizontal section length of 2500m, making it the longest horizontal section recorded in the block. Drilling performance analyses of the well showed that the overall drilling risk, the wellbore construction time, and the drilling costs were substantially reduced by optimizing the drilling operations through geomechanics integrations and applications. The experience and knowledge obtained from this integrated workflow will provide guidance and serve as reference for the efficient development of unconventional oil and gas reservoirs in China.

The challenge was to achieve more reservoir contact in a cretaceous tight reservoir to improve production and maximize recovery. Multilateral well campaigns were performed to meet these objectives.This case study describes an effective workflow for performing openhole sidetracks in this challenging medium-hard carbonate formation. The workflow maintained reservoir contact and achieved the desired production objectives.Two 6-in. multilateral drain sections were successfully drilled by performing openhole sidetrack using the continuous proportional steering method (CPSM). This method is not new to the industry, but this case study describes the systematic, unique workflow that was designed and followed to ensure a successful sidetrack in this low-porosity, hard formation.The sidetrack implementation started by creating humps at inclinations ranging from 88 to 91 degrees into the formation in the original 6-in. section. These humps were confirmed using near-bit inclination data (4.5 ft from the bit) and were identified as the sites for initiating a sidetrack. This paper discusses the best practices that were key to the successful execution of the project in one run on the first attempt.After the sidetrack, use of appropriate combinations of shallow and deep logging-while-drilling (LWD) measurements in the same bottom hole assembly (BHA) enabled the direct geosteering of the well, exposing more reservoir surface area than planned.A reduction of 10% from the planned well duration was achieved. Two 6-in. laterals, each approximately 4000 ft, were drilled in a single run and 100% reservoir contact was achieved.This experience proved that planning and precise execution could enable drilling of openhole sidetracks, even through hard formations. These sidetracks can then achieve fishbone wells with desired reservoir contact and realize the field development objectives in a technically robust and cost-efficient manner.CPSM does not rely on a pressure drop for steering. Although this proof of concept was performed in a relatively hard formation, similar workflows with appropriate drilling engineering may be applied to less-competent formations as well. The detailed procedure and flowchart created from the experience with the sample well can be adopted for use in similar applications.

The Interactive Multi-Model (IMM) algorithm uses multiple motion models to simultaneously track the target, which effectively solves the problem of model mismatch when a single model tracks the maneuvering target, and is widely used in maneuvering target tracking tasks. However, the Interactive Multi-Model recognition motion model is not accurate enough, and there is a certain delay in the maneuver recognition of the target, which leads to a reduction in tracking accuracy. To solve this problem, considering that deep neural networks are very good at processing classification tasks, we introduce it into target tracking tasks, combining the respective of deep neural networks and traditional tracking filtering methods for maneuvering target tracking. we use the Recurrent Neural Networks to identify the motion model of the target and propose an improved LSTM-IMM model algorithm based on the interactive multi-model algorithm. Finally, we compare the traditional interactive multi-model algorithm and verify the algorithm using Monte Carlo simulation. The results show that the proposed algorithm has improved the recognition accuracy and recognition speed of the model, and the tracking accuracy has been improved.

Logging-While-Drilling (LWD) has incorporated almost all wireline-equivalent technology with the added advantage of logging high-angle and horizontal wells with reduced rig time, critical for cost optimization efforts. LWD measurements are affected by a rugged drilling environment, and logging interpretation with a wireline mindset leads to erroneous results. Identifying measurement artefacts from real formation information is critical for reliable log analysis. This publication discusses the most common effects of drilling dynamics and environments on LWD logs that were observed during logging and drilling wells in cretaceous carbonate reservoirs in an Abu Dhabi onshore field. Log data from more than one hundred wells are reviewed to identify several interesting effects due to bottom-hole-assembly (BHA) design, BHA driving mechanism (Rotary steerable system versus mud motor), tool eccentricity, well angle, mud properties, differential invasion, borehole condition, formation fluid properties and lithology. In a few instances, some of these effects occur simultaneously, complicating the log response. These phenomenons are discussed in detail with actual examples and compared to offset wells and response modellings. The rugged logging environment and limited formation damage due to invasion provide a unique opportunity to obtain additional insight about reservoir behavior, especially when compared to wireline data in an offset well or in the same well. Pre-job planning and modelling can use these phenomena for getting additional information about dynamic reservoir behavior. This paper highlights a few such applications. This paper explains the impact of a dynamic drilling environment on LWD measurements and serves as a ready reference to identify measurement artifacts from real formation information. It is helpful as a guidebook for log analysts, geologist, geo-steering engineers and other non-specialists to identify LWD measurement artefacts.

This paper presents the successful use of LWD NMR and LWD resistivity image log technology to meet the challenge of placing wells in a thin reservoir with lateral facies variation without the use of radioactive sources and with simultaneous data acquisition to evaluate the wells and design their downhole inflow control devices (ICDs). A series of horizontal producer wells were planned in a thin reservoir with lateral facies variation. After drilling the wells they were completed with downhole ICDs. Optimum placement of the wells within the reservoir and data acquisition to evaluate the wells and design their completions was achieved without the use of radioactive sources, as these created an unacceptable drilling risk. Rapid and accurate processing of the data in real time and subsequent design of the ICDs was required to enable the completions to run in a timely fashion. The NMR permeability was normalized using the new calibration parameters that were developed by integrating NMR results with core data, and the same relationship has been tested in other lateral wells. Real-time NMR total porosity played a significant part in facilitating effective geosteering and well placement without the drilling risks associated with radioactive sources. In addition, the NMR provided a porosity distribution that was used to estimate a permeability index. This index was normalized using core permeability available from offset appraisal wells. The core and NMR log data in the offset wells were combined to derive the parameters for an NMR permeability relationship. The standard volumetric analysis results and the permeability index were used for identifying reservoir flow units using crossplots of normalized flow capacity versus normalized storage capacity (modified Lorenz Plots). These results were then used to develop the parameters for the ICD completions. High resolution LWD image log data was incorporated to select the best possible sections in the wells for isolation of the ICD segments. Following completion and stimulation, multiphase PLTs were run across the ICD compartments to evaluate the wells. These results were then compared against expectations and used in subsequent well completion designs. The results of the wells presented show that the chosen methodology enables the successful placement and completion of horizontal wells in this reservoir. Decisions about ICD completion design can be made in a timely fashion just after the drilling phase is complete, avoiding rig downtime. This approach has become the default procedure for the field and will be used for the bulk of the remaining producer wells in the reservoir.

The Archie equation is the most common approach for calculating water saturation. The true formation resistivity that is derived from resistivity logs is an important component. In high-angle or horizontal wells (Ha/Hz) the commonly employed induction style tools and multi-propagation resistivity (MPR) tools employed in logging-while-drilling (LWD) have challenges. In particular, at bed boundaries, the formation-to-wellbore geometry affects deep-reading logs and generates artifacts such as so-called polarization horns on the logs. These effects become more significant with increases in the relative dip and the resistivity contrast between the beds. These conditions impair the use of resistivity for water saturation determination. An innovative modeling workflow to generate a true formation resistivity (Rt) from LWD MPR logs is presented. In addition, a number of case examples from Abu Dhabi reservoirs are portrayed. The workflow described in this study begins with the interpretation of borehole image data to build a structural earth model. For this, the picked boundaries are extended away from the trajectory within an investigative volume of the MPR responses and are used to constrain an inversion algorithm that solves for Rt. The inversion is conducted using eight short- and long-spaced apparent phase differences and attenuation data. Different starting models and inversion constraints are applied to evaluate the sensitivity of the inversion results. The inversion results are further qualified from the ‘misfit’ calculated by the inversion algorithm. This methodology was used to process data from multiple wells in a development field near Abu Dhabi. These high-angle wells are from carbonate reservoirs with varying characteristics (such as tight, layered, high-permeability streaks, etc) and all employ LWD measurements. The integrated data of vertical wells formation evaluation, dean stark and dynamic data (well test) were used to validate results of the case study. The processing results showed significant improvement in determining true resistivity that provided highly coherent saturation determination along the entire wellbore profile. It gave confidence in the effectiveness of the approach for an improved quantitative petrophysical evaluation in Ha/Hz wells. This new processing method is able to solve the existing issue associated with LWD measurement in high angle wells thereby improving the saturation calculation significantly.

Reservoir A is an Upper Jurassic reservoir in offshore Abu Dhabi, composing layers of dense anhydrite and porous mixed lithology of dolomite and limestone. Petrophysical study from multiple wells suggests that the rock quality within the reservoir has significant lateral and vertical variations that can result in different flow capacities. Consequently, it is crucial to identify the rock quality variations and the consequent flow capacity in horizontal wells to optimize development plan, ideally in real-time. However, these lateral and vertical variations are not visible from conventional porosity (density / neutron) logs, making identification of rock quality very challenging. This paper introduces an innovative magnetic resonance (NMR)-based real-time method of permeability prediction and rock typing.Wireline logs including NMR were acquired in a pilot well, providing porosity and extensive T2-based information (permeability index, irreducible and movable fluid volume and porosity partition). Routine core analysis was also available to calibrate the NMR data, achieving a suitable correlation for NMR permeability index calibration in this field. Several rock types could be identified with the Windland R35 technique using porosity and calibrated permeability from NMR. This identification was then validated by rock types from cores. The application of knowledge gained from the study led to advanced reservoir characterization solely based on the NMR log. The process was applied to high-angle and horizontal (HAHZ) wells where the NMR full-spectrum log while drilling was available.Several slanted wells were drilled with a fit-for-purpose logging-while-drilling (LWD) suite including NMR for geo-steering and formation evaluation. The real-time LWD NMR data helped trace a remarkable change of irreducible water level through certain layers, suggesting that the subzones of Reservoir A changed pore geometry and rock type laterally, resulting in variations of flow capacity and reservoir performance.In one example, this method indicated unexpected good rock quality in one of these subzones considering the experience from offset well. Subsequently, the LWD formation-testing tool confirmed the result with mobility measurements, proving the NMR-based methodology was valid.This process normally applies to memory data after drilling, playing a key role in designing completion strategy in a timely manner. The process is also available in real-time while drilling if full NMR data is transmitted to surface, serving as a safer logging-tool for identification of sub-zones with additional valuable information compared to regular porosity tools with chemical radioactive source.