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The article deals with the lithology and geochemistry of organic matter of Upper Devonian-Lower Carboniferous deposits (Carbonate Devonian) of the eastern part of the South Tatar arch. Rocks of this age have a high generative potential due to increased concentrations of organic matter (OM) and its phytogenic and zoophytogenic composition. They refer to non-traditional sources of hydrocarbons. The generative potential depends on the facial environment and the transformation of OM. The highest potential have carbonate-siliceous and siliceous-carbonate rhythmites domannic horizon.

A significant part of hydrocarbon deposits in Russia is in the late stage of development. The distribution of residual oil and gas reserves is determined by the properties of the holding rocks. Estimating of deposits’ residual gas saturation is an important scientific task. The allocation of zones with the maximum undeveloped gas reserves will allow to select areas in long-developed fields for the intensification of production in the most efficient way. To search for such “sweet” zones, it is necessary to determine the factors that provide the value of the residual gas saturation. The reliance of the value of trapped in pores, residual gas saturation on such rock properties as pore space structure and wettability is studied in this article. The influence of formation pressure value and behaviour on making up of residual gas saturation during field development is not accounted in this work. The study of a wide collection of core sampled from productive deposits of the Orenburg oil and gas condensate field, the Vuktylskoe oil and gas condensate field, oil and gas field of Orenburg region, and also three areas in the East Caucasian petroleum province confirmed that the value of structure-trapped oil and gas saturation of carbonate and terrigenous rocks is directly proportional to the ratio of pore diameters and channels connecting them. Herewith the angular coefficient of the regression equation for this relationship for carbonate rocks directly depends on the quantitative characteristics of the predominant (relative) wettability. The obtained relationships make it possible to predict the value of residual gas saturation based on knowledge about the pore space structure and the surface properties of rocks.

Core material taken over a section of the Bavly multipay field of Tatarstan (Russia), and extracts from it have been studied by thermal analysis, IR and EPR spectroscopy, and gas-liquid chromatography. The trends of changes in the amount and fractional and hydrocarbon-group compositions of residual oil and oil components irreversibly adsorbed on the rock depending on the age of deposition have been revealed. In rocks from the Trans-Volgian and Dankovian–Lebedyanian horizons attributed to domanik deposits, the organic matter content has been determined with an estimate of the proportion of bitumoid and kerogen in it, and the peculiarities of their fractional and hydrocarbon-group compositions have been revealed.

Core material taken from Zavolzhsky and Dankovo-Lebedyan horizons of the Bavly oil field attributed to the Domanic deposit is studied by thermal analysis methods. The content of total organ...

The experiments carried out on a physical model of reservoir of ultra-viscous oil have revealed features of oil displacement in various variants of the composite solvent and steam injection. In order to avoid precipitation of asphaltenes, the employment of inhibitors has been rationalized and their minimum fraction in displacement fluid has been determined. The effect of the sequence of solvent and vapor injection on the dynamics of ultra-viscous oil recovery has been investigated. The effect of clay and water in the rock on the rate of oil displacement and the ultimate oil recovery factor has been evaluated.

Today in the oil and gas industry there is a large number of different classifications of hydrocarbon reserves and resources, each of which has advantages and disadvantages. This work includes analysis, comparison, as well as the possibility of comparing the results obtained at first glance, seemingly, from completely different methods of assessment of hydrocarbon reserves and resources. The purpose of the paper is to consider the features of calculating hydrocarbon reserves by different methods and to study the feasibility and appropriateness of applying the probabilistic method for reserves audit. The oil reserves were calculated by volumetric method based on the geological model of the deposit, constructed using the IRAP RMS software package. The variability of the counting parameters was specified in the “Uncertainty” module, with the help of which it is possible to build a geological model with equiprobable realizations, having insufficient data on the main characteristics of the field. When calculating the uncertainty, the variance by values was set for the following parameters: water-oil contact level, recalculation factor, porosity and water saturation coefficients. After computation and enumeration of possible implementations within the given parameters, the program generated the result in the form of three reserve values: P10 (probable), P50 (possible), P90 (proved). To compare the results of the reserves calculation, the resulting oil-saturated thickness maps were used to trace the distribution of geological reserves. Based on the conducted research, it was revealed that input data and a different approach to the construction of the 3D geological model influence the final result in the distribution of the reservoir and the main parameters in the volume method formula. For a correct figure of hydrocarbon reserves (resources), it is necessary to use a multivariate distribution of counting parameters in the geological space of the considered object.

The oil generating potential of Domanic rocks from Dankov–Lebedyan horizon of the Zelenogorsk area of Romashkino oil field was evaluated by Rock-Eval pyrolysis technique. The result of given method...

The oil generation potential of low permeability carbonate reservoir rock from the Dankov-Lebedyan horizon of the Domanikovian deposits of the Upper Devonian of the Zelenogorsk area of the Romashkino field is evaluated as a function of content and composition of the organic matter in the reservoir rock and of the composition of the shale oil extracted from the rock by organic solvents. In comparison with the shale oil produced from the carbonate reservoir rock of coeval deposits by hydrofracking of the rock formation, the extracts from the rocks contain more resins and asphaltenes and less saturated fractions predominantly comprised of high-molecular-weight n-alkanes. In model experiments, the influence of the temperatures 20, 250, 300, and 350°C on the conversion of organic matter of the Domanikovian carbonate rock in a carbonic acid hydrothermal system are studied, and the yield and quality of the extracted hydrocarbons are evaluated. It is demonstrated that the thermal effect at 200 and 250°C on the rock facilitates more intense and complete extraction of oil hydrocarbons. Processes of degradation of high-molecular-weight components and insoluble kerogen occur at temperatures above 300°C, leading to an increase in then yield of extracts from the rocks and an increase in them of the content of saturated hydrocarbons whose composition approaches the composition of the shale oil extracted from low permeability carbonate reservoir rock. Results of the investigation provide grounds for suggesting that carbonate rock of the Dankov-Lebedyan horizon contains productive formations that could become an additional source of petroleum hydrocarbons when developed by hydrothermal technologies.

The emerging problems of the long-term sustainability of the Russian oil industry, including Tatneft, in conditions of low world oil prices must be solved through more efficient use of costs, especially capital investments in the construction of new production wells. Along with various methods of increasing the oil recovery factor and intensification of oil production, one of the main ways to improve the profitability of wells is the construction of wells with horizontal end. Greater prospects for the use of horizontal wells are expected in the Timanian deposits of the Romashkino field. The use of a controlled valve (curtain) to open/close the inflow from the section of the horizontal trunk will significantly reduce the water cut of well and, accordingly, increase the share of oil per ton of produced liquid.

The paper considers efficient development of Domanic reservoirs in Tatarstan using multistage fracturing technology in horizontal wells, based on the analysis of developing Shaly Carbonates in the United States, which are the closest in terms of geological and physical characteristics. Simulation in the software product GOHFER was carried out. Three types of multistage fracturing were considered: acid, proppant, and combined. Calculations show that practically all types of multistage fracturing with 5 stages are either not profitable, or are on the verge of profitability. Acid and combined multistage fracturing are the most effective at 10 stages; net discounted income for 5 years of operation is 90-100 million rubles. All three types of multistage fracturing are effective at 20 stages; acid and combined multistage fracturing are also characterized by the biggest net discounted income of 240-280 million rubles.

As a result of a series of experiments for the physical modeling of oil displacement processes on a large model, specific features of asphaltene sedimentation and immovable residual oil formation in a porous medium were identified. The difference between the residual oil compositions was shown in the zones of dispersive and diffusive oil displacement by solvent. The impact of the solvent composition on the asphaltene concentration in the residual oil in a reservoir model and the cumulative oil recovery was assessed upon the example of the Ashalchinsk field ultra-vicious oil using n-hexane as a basic solvent with toluene and nonylphenol additives.

In connection with the growth of oil reserves difficult to recover in the structure of reserves, the task of efficient development is becoming more complicated. The development of carbonate reservoirs having a complex structure and containing heavy oil is caused by the low rates of extraction and values of oil recovery factors. At present, there are no low-cost technologies that ensure high efficiency of development of such fields. The pilot site of the Bashkirian stage drilled with wells of various structure was considered, including the first in the Republic of Tatarstan experience of drilling complexly designed wells with two horizontal boreholes in complex carbonate reservoirs containing heavy oil and selective operation of each borehole using double elevator unit of dual completion. The average characteristics of wells with various designs are compared, and measures for improving efficiency of further exploitation of these wells are given.

Objectives The sustained long-term development of oil industry in Russia depends largely on how effectively oil reserves in the domanik sediments and other hard-to-recover reserves are brought on stream. Study and development of the domanik sediments–tight, low-permeability carbonate rocks–requires heavy investments and significant intellectual assets. The main challenge of nowadays’ is to find effective stimulation methods to enhance production from the domanik sediments. Development of technologies that can give insight into the reservoir dynamics to make decisions on the optimum completion strategies is one of the priorities of PJSC TATNEFT. Currently, common stimulation methods include treatments of the bottomhole zone and hydraulic fracturing. So, the focus is on the technologies that help to understand the process of hydraulic fractures propagation into the reservoir in the process of multistage hydraulic fracturing, to estimate the extent of the stimulated reservoir volume, and to assess zones of likely proppant penetration into fractures.

Summary One of the type of well-known smart waterflooding is injection of different nanoparticles mixed with low-salinity or formation water. Previous studies showed a good potential of the nanoparticles as EOR method. But the biggest restriction of full-field applying is the cost of the nanoparticles. We found out that products of different factories, electric power plants etc. could be used as the nanoparticles for EOR technologies and expenses for its preparation are much lower. This paper presents the results of laboratory studies and 3D simulation of water injection with Ca, Si and Al-based nanoparticles into a carbonate oil reservoir. Laboratory studies included preparation of cores, scanning of cores and double core flooding using formation water and the same water with nanoparticles. Then the injection was simulated at 3D pilots of the carbonate reservoir of the Romashkinskoe field. Laboratory tests and 3D simulation showed that the incremental oil recovery with injection of the nanoparticles is around 15–27% (displacement coefficient) and 2–5% (recovery factor) respectively. The nanoparticles are much smaller than pore throats. Thus, we assume that the effect could be explained by reduction of interfacial tension and some wettability alteration.

The model experiments regarding the conversion of organic matters from carbonate rock samples of Dankov-Lebedyan deposits of Zelenogorskaya area and siliceous-carbonate rocks of Semiluki-Mendym deposits of Berezovskaya area of Domanic formations of Romashkino oil field were carried out. Two types of experiments were carried out: (1) the hydrothermal treatment of rocks at a temperature of 350°C in the presence of carbonic acid and a water content of 30%; (2) pyrolysis at temperatures of 350 and 600°C in the presence of hydrogen. The yield and quality of extracted hydrocarbons from the rocks depending on the mineral composition of rocks, content and composition of organic matter, and thermal stability of kerogen under hydrothermal influences were evaluated. Application of electron paramagnetic resonance in pyrolysis processes revealed the difference in mineral content of rocks (Mn2+, SO3−, and SO2− ions) and free radicals R∗, as well as in vanadyl ion (VO2+) concentration. It is established that an increasing temperature of pyrolysis promotes the formation of new free organic radicals in rock samples: in Domanic rocks of Semiluki-Mendym deposits at 350°С and in carbonate rocks of Dankov-Lebedyan horizon at 600°С. This indicates different ability of oil-generating potential of rocks with hydrothermal and pyrolysis technologies.

Low salinity waterflooding is presently one of the most promising enhanced oil recovery (EOR) methods. Wettability alteration and residual oil decrease are the most important EOR mechanisms of low salinity waterflooding. However, the mobility control EOR due to fines migration, induced by low salinity water, and the consequent flux diversion is also an important feature of the smart waterflooding. We analyze the limited available field data from 10 years of low salinity water injection in Bastrykskoye field. The mathematical model for fines-assisted waterflooding is used for history matching resulting in good agreement between the field and modeling data. The model is used to compare recovery factor for two scenarios of low salinity water injection and formation (normal) water injection. Low incremental recovery and low decrease in the amount of produced water during the development of Bastrykskoye field is explained by the production of significant amount of the reservoir water before the commencement of...

Low salinity waterflooding is a very promising EOR method in recent years. The mechanisms of enhanced recovery are considered to be decrease of residual oil saturation and alternation of rock wettability. In addition, the mobility control mechanism due to induced fines migration by low salinity water, and the consequent flux diversion is also a possible mechanism for enhanced recovery in low salinity waterflooding. The current paper analyzes production and injection history data from 24 years of production from Zichebashskoe field (Russia) which includes 7 years of low salinity water injection. The mathematical model for waterflooding with fines migration is applied for history matching. The result is a good agreement between the field history and modelling data. The Roxar tracer model is then used to compare recovery factor for two scenarios of low salinity water injection (field history) and conventional water injection using formation water (High salinity). The results shows insignificant incremental recovery ( 45% of total produced water) before the commencement of low salinity water injection and also injectors placing. A two layer cake reservoir is built using Zichebashskoe field permeability distribution to study the effect of low salinity water injection in a 5 spot pattern. Modeling results show significant improvement in oil recovery (~10%) and large reduction of water cut.

Main fields in the Republic of Tatarstan have entered the closing stage of development characterized by high extent of reserves depletion (86 % of OOIP) and increase of the share of unconventionsl hard-to-recover reserves (from 33 % to 80 %). A considerable portion of PJSC TATNEFT’s unconventional reserves (36 %) is found, primarily, in carbonate and carbonate-silicious (shale) low porosity/permeability or fractured reservoirs, which are very challenging targets. In this light, study of low-permeability and porous reservoirs has recently acquired a prime importance. Comprehensive studies are needed to understand stress and strain properties of reservoir rocks in challenging geomechanical in-situ conditions. To understand fracturing pattern of carbonate reservoirs in Tatarstan, the Company has been employing different survey methods, including aerial and space imagery, side-view seismic location (SVSL), offset vertical seismic profiling, tracer surveys, core analysis, including oriented and quick capture cores, 3D CDP seismic survey. Particular attention has been given to analyses of drilling troubles and vertical and horizontal wells’ performance. The results obtained make it possible to select optimal orientations of horizontal wellbores with a view to maximize future production. This paper presents the Bavlinskoye oil field case study. Recommendations on downhole surveys are presented, as well as guidelines to select an optimal orientation of a horizontal wellbore in fractured reservoirs.

The objective of the paper is to assess incremental oil production due to low-salinity waterflooding (LSW) in the Pervomaiskoye oil field operated by PJSC TATNEFT vs. conventional waterflooding by high-salinity water. In this field, low-salinity water has been injected for a relatively lengthy period enabling to assess the effects of low-salinity flooding. The procedure was as follows. Laboratory coreflood experiments included preparation of cores, their saturation with formation water and oil, core flooding using high-salinity and low-salinity water. In both cases, oil production was recorded and fines release was analyzed. Core test results were adjusted using a special numerical fines migration model, and relative permeabilities were calculated. Then a 3D model was built and history matched using the function that allows change of relative permeability to water. After this, the model was recalculated without this function and incremental oil production due to LSW was estimated. 3D modeling showed that cumulative additional oil production due to LSW in Pervomaiskoye oil field is 4.2 million m3, incremental oil recovery is 3.5 %. The effect was prominent in wells with wellstream water cut from 20 % to 90 %. Targeted application of LSW is recommended – in injection wells as an EOR method when wellstream water cut ranges from 20 % to 90 %, and in production wells as a water control technology.