Oil Saturation In Reservoir Research Articles

Reservoir evaluation method for complex resistivity using the borehole–surface electromagnetic method: A case study of an igneous reservoir in the K exploration area, China

Electrical well-logging techniques, combined with electrical conductivity models, have been widely used to estimate oil saturation levels in hydrocarbon reservoirs. For complicated and heterogeneous petroleum reservoirs, however, evaluation results are inevitably limited by well locations. Recent studies have indicated that the borehole–surface electromagnetic method (BSEM) can detect electrical characteristics distal from a well, and it can be applied to delineate the boundaries of complicated reservoirs. Therefore, in the study described here, a new method to estimate reservoir oil saturation, based on the BSEM, has been developed. In this work, we deployed the BSEM in a designated study area, obtaining complex resistivity and polarizability data, through the constrained inversion of the re-weighted regularized conjugate gradient method. Based on the petrophysical analyses, we developed a new saturation evaluation model, composed of a parallel circuit connection between formation water and the polarization induced by the porous medium containing clay minerals. The effectiveness of the new model was verified with a synthetic dataset generated using Archie's law and the improved Dias model. We found that the target reservoir oil saturation results calculated using the new oil saturation model were in good agreement with applicable nuclear magnetic resonance log data, thus verifying the validity of this new BSEM evaluation technique.

Insight into pore-throat size distribution and the controls on oil saturation of tight sandstone reservoirs using nuclear magnetic resonance parameters: A case study of the Lower Cretaceous Quantou Formation in the southern Songliao Basin, China

Pore-throat structure characterization is crucial in tight-oil sandstone reservoir studies. To better understand pore-throat size distribution and the effects on reservoir oil saturation, petrographic, scanning electron microscopy, quantitative grain fluorescence (QGF), nuclear magnetic resonance (NMR), and pressure-controlled mercury injection investigations were performed on a suite of tight sandstones from the fourth member of the Lower Cretaceous Quantou Formation (K1q4) in the southern Songliao Basin, China. The tight sandstone samples showed similar compositional and textural maturity but different reservoir qualities at different depth intervals. Two oily indicators, QGF index and QGF on extract spectra intensity, varied significantly with respect to burial depth, suggesting the existence of strong oil heterogeneities in the K1q4 tight sandstones. Oil emplacement occurred mainly in the primary pores associated with the absence of pore-filling authigenic minerals. Pore-throat size distributions had wider ranges in the oil-rich layers than in the samples lacking oil emplacement. The NMR pore-throat radii ranged from 0.01 to 10 μm in oil lacking samples but ranged from 0.01 to 100 μm in oil-rich layers. Oil signals were mainly detected in the pore throats with radii ranging from approximately 0.1 to 1.0 μm in oil-rich layers. The NMR porosity can be divided into three parts based on transverse relaxation time (T2) spectrum: (1) immovable fluid, (2) porosity of effective movable fluid (PEMF), and (3) porosity of bound fluid. Bivariate plots of the ratios of various porosity types have significant effects in deciphering the oil saturation of tight sandstone reservoirs. The PEMF reflected well the reservoir QGF index, among others. Therefore, it can be considered as an effective NMR parameter to characterize pore size distribution and helpful in oil reservoir prediction. A good relationship exists between PEMF and geometric mean of the T2 distribution (T2gm), indicating that T2gm could also reflect reservoir oil saturation. The PEMF is mainly contributed by large pore throats, and the poorly sorted pore-throat distribution is better for effective movable fluids occurrence in tight sandstones. The approach employed in this study provides a more comprehensive and accurate pore-throat structure characterization in tight sandstone oil reservoirs, generating effective parameters and convenient ways to evaluate reservoir oil saturation. Importantly, it could be applicable for improving tight sandstone oil exploration and development efficiencies.

Study of thin layered reservoirs with toroidal sources and receivers (on the example of the Priobskoe oil field)

On the example of the Priobskoye oil field of the West Siberian oil and gas province, we show the relevance of studying thin-layered oil-saturated reservoirs, as well as consider the corresponding world experience. The operating principle of a probe system with toroidal sources and receivers is described, after which we perform 2D finite-difference simulation and analysis of its signals in typical geoelectric reservoir models. The dependence of the signals on the resistivity anisotropy coefficient is demonstrated. In realistic geoelectric sections of the Priobskoye field, obtained by numerical inversion of BKZ field data, 2D finite-difference simulation for the system with toroids is conducted. It implies the fundamental possibility of investigating thin-layered electrically anisotropic deposits of the Priobskoye field by means of the system with toroidal sources and receivers.

The nature of the formation in clay strata of oil and gas saturated fractured reservoirs

Today, the production of hydrocarbons produced from clay strata of varying degrees of consolidation and metamorphization had widely developed in the world. Currently, there are many hypotheses on the formation of reservoirs in industrial oil-bearing clay rocks. The paper analyzes the mindsets on the occurrence of oil-saturated fractured clay reservoirs, presents factors affecting the distribution of radioactive elements, substantiates the mechanism of formation of fractured porosity in clay oil-saturated strata. Due to the lack of a generally accepted concept for the formation of unconventional clay reservoirs, the article proposes a new hypothesis for the formation of fractured reservoirs in these unique sections, based on a critical analysis of existing views.

СРАВНИТЕЛЬНАЯ ПЕТРОФИЗИЧЕСКАЯ ХАРАКТЕРИСТИКА ЮРСКИХ РАЗРЕЗОВ ОСТАНИНСКОГО И ДВУРЕЧЕНСКОГО МЕСТОРОЖДЕНИЙ (В СВЯЗИ С НЕФТЕГАЗОНОСНОСТЬЮ ДОЮРСКИХ ОТЛОЖЕНИЙ ТОМСКОЙ ОБЛАСТИ)

Актуальность исследования обусловлена важностью воспроизводства и расширения ресурсной базы углеводородов Западной Сибири на основе оценки перспектив и освоения горизонта зоны контакта и коренного палеозоя, залежи в которых относятся к трудноизвлекаемым запасам. Цель: последовательное обоснование критерия прогнозирования и поисков палеозойских залежей углеводородов, основанного на гипотезеаномальности петрофизических характеристик юрских пластов – уникальности «отражения» залежей палеозоя в геофизических параметрах перекрывающего мезозойско-кайнозойского разреза. Эта гипотеза была сформулирована и аргументирована ранее результатами изучения разрезов скважин Герасимовского месторождения с палеозойскими залежами нефти и Крапивинского месторождения с юрскими залежами нефти. Объекты: геофизические и петрофизические параметры юрских пластов-коллекторов и интервалов баженовской свиты на Останинском нефтегазоконденсатном месторождении, имеющем залежи в доюрском основании, и на Двуреченском нефтяном месторождения только с юрскими залежами нефти. Методы. Для характеристики юрских пластов-коллекторов выполнены петрофизические расчеты удельного электрического сопротивления, использовались данные индукционного каротажа и каротажа сопротивления по разрезам 28 скважин Останинского и Двуреченского месторождений. Для характеристики петрофизики аргиллитов баженовской свиты сделан качественный и количественный (статистический) анализ показаний методов потенциалов самопроизвольной поляризации, кажущегося сопротивления и гамма-каротажа. Карбонатность пород пластов-коллекторов оценивалась по данным объемного газометрического метода. Результаты. Установлено, что юрские пласты-коллекторы Останинского месторождения имеют для нефтенасыщенных пластов УЭС=11…21 ом*м, для водонасыщенных пластов УЭС=5…9 ом*м. Юрские пласты-коллекторы Двуреченского месторождения имеют для нефтенасыщенных пластов УЭС=6…12 ом*м, для водонасыщенных пластов УЭС=2…5 ом*м. Юрские пласты-коллекторы Останинского месторождения аномально, в 2 раза, более высокоомные, чем юрские пласты Двуреченского месторождения. Общая карбонатность юрских пластов Останинского месторождения составляет 5,4 %, а Двуреченского – 1,1 %. Показано, что на Останинском месторождении вариации показаний метода ПС= ±(0,5…2,5) мВ, уровень УЭС=32…42 ом*м, уровень естественной радиоактивности 36…44 мкР/ч. На Двуреченском месторождении вариации показаний ПС – ±(5,0…8,0) мВ, уровень УЭС=95…111 ом*м, уровень естественной радиоактивности 40…59 мкР/ч. Результаты исследований на Останинском и Двуреченском месторождениях полностью согласуются с ранее высказанной и аргументированной гипотезой аномальности петрофизических характеристик юрского разреза, перекрывающего залежи доюрского НГК.

Downhole System Enables Real-Time Reservoir-Fluid-Distribution Mapping

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper IPTC 19807, “A New Downhole System for Real-Time Reservoir-Fluid-Distribution Mapping: E-REMM, the Eni Reservoir Electromagnetic Mapping System,” by Franco Bottazzi, Paolo Dell’Aversana, and Claudio Molaschi, SPE, Eni, et al., prepared for the 2020 International Petroleum Technology Conference, Dhahran, Saudi Arabia, 13-15 January. The paper has not been peer reviewed. Copyright 2020 International Petroleum Technology Conference. Reproduced by permission. This paper presents the basic concepts and architecture of the Eni Reservoir Electromagnetic Mapping (E-REMM) borehole electromagnetic (EM) mapping system that integrates borehole EM methodology with surface EM methods to provide real-time mapping of reservoir-fluid distribution during production or injection. By helping well teams know how distribution of hydrocarbons and water changes over time and space, the system addresses a fundamental requirement for managing the reservoir to maximize the recovery factor, optimize production, and reduce associated costs. Introduction Several approaches are currently used to map hydrocarbons and other fluids in the reservoir in real time with variable sensitivity, differences in effectiveness, and a wide range of costs. Among the various approaches, EM and electric methods show a high benefit-to-cost ratio and a high sensitivity to the resistivity contrast between oil-saturated and brine-saturated reservoir rocks. These methods can estimate variations in fluid properties at reservoir depth in a distance range of hundreds of meters, although the spatial resolution decreases significantly with the distance between sources and receivers. Furthermore, combining multiple layouts in boreholes and at surface can improve the effectiveness of EM and electric methods significantly while increasing their spatial resolution. The integrated system discussed in the complete paper allows multiscale EM prospecting and deep investigation in a large 3D volume of rocks between multiple wells and surface.

Oil recovery mechanisms of Pickering nanoemulsions stabilized by surfactant-polymer-nanoparticle assemblies: A versatile surface energies’ approach

In this article, we present a holistic approach to predict the interfacial activity of surfactant/polymer/nanoparticle stabilized Pickering nanoemulsions. Dynamic interfacial tension was measured and their profiles were generated in real time using pendant drop technique. The free detachment energies (Edet) at liquid-liquid interface decreased with time owing to gradual slipping of emulsifier(s) toward oleic phase, which translates to favorable oil displacement. Crude oil miscibility experiments confirmed synergistic influences of gemini surfactant, partially hydrolyzed polymer and silica nanoparticles. However, it was recognized that these investigations do not consider effects of rock mineralogy and solid-liquid dynamics, and hence, must be replaced with an evolved surface wetting approach. A “modified” Arrhenius model is tailor-made for nanoemulsions (as oil displacing fluids) to determine the surface activation energies and mechanistically discuss the altered wettability state of reservoir rock(s). Surfactant-polymer-nanoparticle (SPN) nanoemulsion exhibited enhanced oil displacement as compared to surfactant-stabilized and surfactant-polymer stabilized nanoemulsions. In summary, the surface energy approach was corroborated from theoretical as well as experimental investigations. Qualitative investigation of SPN nanoemulsion-based oil displacement was performed via microscopic imaging, infrared spectroscopy and wettability alteration technique by mimicking different flooding stages in oil-saturated reservoir models for application in enhanced oil recovery (EOR).

ОЦЕНКА ЭФФЕКТИВНОСТИ МЕТОДА ФИГУРНОГО ЗАВОДНЕНИЯ

Methods of regulating the development of oil and gas fields play an important role in ensuring rational selection rates at the highest values of reservoir component recovery coefficients. The applied methods allowed the most rapid selection of recoverable oil reserves, but nevertheless, over time, many individual areas of the deposit were identified, whose reserves were developed at a low rate. Therefore, to improve the development of hard-to-recover reserves in these areas, zones, additional methods of influence are used by injecting a certain volume of water into the reservoir through new injection wells created by drilling them or transferring existing high-water wells for injection. At the same time, work is being carried out in existing wells to increase their productivity. This article discusses the application of figure flooding method as an additional method of regulating the development process of the Uzen deposit. The authors presented the results ДОБЫЧА 112 НЕФТЬ И ГАЗ 2020. 3–4 (117–118) of analysis of exploitation of oil areas of figure flooding. A study was conducted to identify the technological effect of the use of the figure flooding method. Figure flooding contributed to unsteady state fluid flow in reservoirs, which led to the reduction of water production wells before working intervals and also in some areas.This method hashad a positive impact on the development process by connecting new production intervals to the operation. The inclusion in the development of new productive formations and layers led to an increase in the flow rates of wells and oil production, as well as simultaneously to a decrease in the flow rates, liquid production and water cut. The quantitative assessment of efficiency was carried out by comparing the corresponding actualandcalculatedtechnological indicators.Thepaperpresentsanalyticalformulas thatwereused to calculate changes in the analyzed data in case there was no specified method. The calculated values of oil and liquid flow rates and water level of sections of the XIV and XV horizons were determined under the assumption that there would be no figure flooding. The results of calculations of technological indicators and processing of actual data, as well as the technological advantages of individual sections are presented. It is established that the use of shaped flooding in the complex will allow full connection to the work of new oil-saturated reservoirs, if new independent systems of arrangement are created to ensure the appropriate hydrodynamic parameters of pressure at the mouths and faces of injection and production wells

ОСОБЕННОСТИ ПОСТРОЕНИЯ ГЕОСТАТИЧЕСКИХ МОДЕЛЕЙ ЗАЛЕЖЕЙ В АКШАБУЛАКСКИХ ОТЛОЖЕНИЯХ АРЫСКУМСКОГО ПРОГИБА

The features of constructing a geostatic model (GSM) of the Akshabulak productive horizon in the composition of oil-saturated reservoirs Yu-0-0, Yu-0-1, Yu-0-2 and Yu-0-3 are considered. Modern approaches to the integration of the accumulated geological and geophysical data into the GSM require the necessary work, primarily such as sedimentological examination of the core and its integration with the results of logging and seismic data. The correct formulation of the problem, its support by the customer at all stages, due to which a close connection between the performed studies and production requests was ensured, were the key to obtaining a high-quality result when solving a seemingly ordinary modeling problem

Efficiency Analysis of the Geological-Technical Activities in Severo-Ostrovnoe Field

The work is devoted to identifying the most relevant geological and technical measures carried out in Severo-Ostrovnoe field from the period of its development to the present. Every year dozens of geotechnical jobs (GJ) are carried out at each oil field-works carried out at wells to regulate the development of fields and maintain target levels of oil production. Today, there are two production facilities in the development of the Severo-Ostrovnoe field: UV1a1 and BV5. With the help of geotechnical jobs, oil-producing enterprises ensure the fulfillment of project indicators of field development (Mikhailov, N.N., 1992. Residual Oil Saturation of Reservoirs Under Development. Moscow, Nedra. p.270; Good, N.S., 1970. Study of the Physical Properties of Porous Media. Moscow, Nedra. p.208). In total, during the development of the Severo-Ostrovnoe field, 76 measures were taken to intensify oil production and enhance oil recovery. 12 horizontal wells were drilled (HW with multistage fracking (MSF)), 46 hydraulic fracturing operations were performed, 12 hydraulic fracturing operations were performed at the time of withdrawal from drilling (HW with MSF), five sidetracks were cut; eight physic-chemical BHT at production wells; five optimization of well operation modes. The paper analyzes the performed geological and technical measures at the facilities: UV1a1∦BV5 of the Severo-Ostrovnoe field. Four types of geological and technical measures were investigated: hydraulic fracturing, drilling of sidetracks with hydraulic fracturing, drilling of horizontal wells with multi-stage hydraulic fracturing, and physic-chemical optimization of the bottom-hole formation zone. It was revealed that two geotechnical jobs, namely, formation hydraulic fracturing (FHF) and drilling of lateral shafts in the Severo-Ostrovnoe field are the most highly effective methods for intensifying reservoir development and increasing oil recovery. SXL was conducted at 5 wells. The average oil production rate is 26.6 tons per day, which is the best indicator. Before this event, the production rate of the well was 2.1 tons per day. Currently, the effect of ongoing activities continues.

МОДЕЛИРОВАНИЕ ГЕОЛОГИЧЕСКОГО СТРОЕНИЯ ПРОДУКТИВНЫХ ОТЛОЖЕНИЙ ВИКУЛОВСКОЙ СВИТЫ

Актуальность. Задачи поисков, разведки, оценки ресурсов и запасов, проектирования, разработки решаются на основе геологических моделей. Наряду с тем, что современное геологическое моделирование позволяет получить трехмерное описание строения геологического объекта, изучить характер и изменчивость параметров пласта и насыщающих его флюидов, оно также позволяет оценить неопределенности, неизбежно возникающие при моделировании геологического строения пласта. Из этого следует, что точность решения любой геологической задачи в существенной степени определяется адекватностью трехмерной модели соответствующего объекта. Таким образом, появляется необходимость привлечения для построения моделей, кроме эмпирических данных, всех видов априорной и косвенной информации – в частности, концептуальной седиментологической модели. Цель: усовершенствование методики построения трёхмерных геологических моделей, учитывающей особенности условий седиментации. Это обусловлено тем, что именно литофациальные характеристики продуктивных отложений являются основными факторами неоднородности природных резервуаров и нефтенасыщенности пород-коллекторов. Методика, учитывающая фациальное строение залежей, позволяет построить дискретно-непрерывную трехмерную модель, более адекватно описывающую изучаемый геологический объект и обладающую заметно более высокими прогностическими свойствами. Объекты: продуктивные пласты викуловской свиты Ем-Еговского лицензионного участка. Методы: детальная корреляция, усовершенствованная электрометрическая методика фациальной диагностики отложений, детерминистические и стохастические методы двухмерного и трехмерного моделирования геологических параметров. Результаты. По данным керна и материалов геофизических исследований скважин с использованием усовершенствованной методики В.С. Муромцева построена фациальная модель, включающая следующие группы фаций горизонта ВК1 викуловской свиты: дальняя зона пляжа, переходная зона пляжа и предфронтальная зона пляжа. С учётом данных по вновь пробуренным 192 скважинам проведена детальная корреляция горизонта ВК1. По её результатам внутри пласта ВК1 выделено три седиментационных цикла, для которых характерна довольно хорошая выдержанность по площади. На основе более точных данных сейсмики и данных 192 вновь пробуренных скважин с использованием концептуальной модели обстановок седиментации создана уточнённая модель залежи горизонта ВК1 Ем – Еговского месторождения. Согласно построенной модели, представления о геологическом строении залежи горизонта ВК1 изменилось значимо. Внешняя проверка подтвердила более высокую точность, а значит, и более высокие прогностические свойства созданной геологической модели. Согласно уточнённому строению, уменьшилась площадь и нефтенасыщенные толщины залежи, и как следствие геологические запасы. Уточнение и детализация строения залежи горизонта ВК1 позволит повысить эффективность доразведки слабо изученных частей и разработки. Предлагаемая в работе модель использована для создания гидродинамической модели и для обоснования наиболее эффективных геолого-технических мероприятий.

Morphological and Lithogenetic Classification of the Carbonate Rocks of the Abalak–Bazhenov Complex

The most prospective intervals of the Bazhenov (Tutleim) and Abalak formations are composed of interbedded siliceous and carbonate rocks. Based on core analysis data, detailed descriptions of the lithogenetic types of carbonate rocks were prepared with the objective of improving their prediction accuracy and the varieties that are most promising for the discovery of oil-saturated reservoirs were determined.

Morphologic and litogenetic typing of carbonat rocks of the Abalak-Bazhenov complex

The most prospective section intervals in the Bazhenov formation (Tutleimskoy) and Abalak formation are composed of interbedded siliceous and carbonate rocks. Based on the core analysis, genetic typing of carbonate rocks was performed to improve the quality of their prediction, the most promising of them for finding of oil-saturated reservoirs are identified.

Influence of asphaltenes on wettability of gas and oil saturated reservoir rock

The wettability of terrigenous and carbonate rock cores of oil and gas condensate fields extracted with n-hexane and chloroform by asphaltenes was studied. The obtained values of core wettability with asphaltenes show their contribution to the change of wettability of different rocks.

Source\u2013reservoir chart for tight oil sweet spots evaluation and its application in Permian of Jimsar Sag, Junggar Basin

Sweet spots control the production of the tight oil reservoir, so sweet spots evaluation is a critical work for tight oil exploration and development. This paper proposes a source–reservoir chart method for tight oil sweet spots evaluation and an application in Permian of Jimsar Sag, Junggar Basin. Firstly, the evaluation chart is plotted based on the relationships between the TOC and Ro parameters of source rocks, the porosity and the oil saturation of reservoirs through the experimental data of hydrocarbon generation simulation and mercury injection. Secondly, according to the evaluation criteria of TOC, Ro of source rock and porosity, oil saturation of reservoir in the study area, the chart is divided into three sweet spots zones and a non-sweet spots zone. Finally, each grid of the study area is assigned parameters and plotted in the chart of different zones, and the sweet spots are mapped. Production data show the reliability of the evaluation results. This method provides a convenient and efficient procedure for evaluating sweet spots of tight oil based on integrating the quality of source rocks and reservoirs.

One-Dimensional Simulation of the In-Situ Oil Combustion with Consideration to Fluid and Solid Combustible Components

The one-dimensional axisymmetric problem of initiation of a combustion wave in an oil-saturated reservoir is solved numerically. Two combustible components, viz. liquid (oil) and solid (kerogen, oil sorbate) were considered. The influence of the abovementioned components on time of the hot site ignition and combustion front speed was simulated and analyzed. It was demonstrated that growth of the mass fraction of liquid component (the total heat content being preserved) results in retard of formation of the hot site near the well and in reduction of the maximum temperature of the combustion wave, disregarding of the higher reactivity of liquid combustible. Simulation revealed existence of the two “peaks” of thermal front velocity. The first one corresponds by time to ignition of combustion site. The second one corresponds to a moment when the solid component combustion front overrides the oil displacement front. Calculations shown, that thermal wave propagation velocity, at least after passing the “peaks” and transition to quasi-steady regime, does not considerably depend on mass traction of the fluid component in the system. A typical term of the exothermic reaction site formation may increase from 50 to 200 days in case of growth of the liquid component content from 30 to 80 mass % at the considered thermal conditions in the oil reservoir. Thus, the implementation of the thermo-gas method in high-productive layers increases the likelihood of difficulty of initiation of a fire. Therefore, the study of the regularities of intra-combustion in such cases is of a particular interest. For instance, the task of combustion site ignition may be resolved by increase of oxygen content in blowing-gas or by means of non-steady (periodical) blowing. It is found that taking into consideration of highly reactive liquid component results in widening (diffusion) of the thermal front, which may play positive role in its spatial thermo-hydrodynamic stabilization. The results of simulation may be utilized for development of technical projects of oil recovery via in-situ combustion, for designing of furnaces utilizing multicomponent fixed layer fuels and for thermochemical investigation of multicomponent fuels.

Large undiscovered oil resources are predicted south of Russia

Stavropol Region is one of the oldest petroleum provinces on South of Russian Federation. Today, most of its fields are depleted and prospects for the discovery of new large hydrocarbon deposits considered exhausted. However, our studies allow us to talk about the possibility of the existence of previously undiscovered oil reservoirs, clamped in the source rocks associated with North-Stavropol tectonic element. In the middle of the last century, similar deposits have been identified within Prikumsk-Tyulenevskiy (Praskoveyskoe, Achikulakskoye, Ozek-Suat and a number of other fields) and Chernolesskiy (Zhuravskoye, Vorobyevskoye) tectonic elements. However, these findings were largely spontaneous due to lack of approved and unified approach to the petrophysical evaluation of dedicated reservoirs from well logs. At the same time the experience of shale reservoirs studies, as well as the results of its implementation to evaluation of deposits of Zhuravsky-Vorobyevsky petroleum accumulation zone, allows to revise existing well log materials for deep wells of explorational and depleted structures, and to identify promising intervals for further re-exploration and testing. In this work, Paleocene sediments of Blagodarnenskaya explorational structure of the Stavropol Region were studied. Despite the approval of the oil bearing of these deposits within the Prikumsk-Tyulenevskiy tectonic element and the positive signs of hydrocarbon saturation from initial well logs data, its evaluation and testing within Blagodarnenskaya structure associated with North-Stavropol tectonic element, were not conducted. However, the results of well logs analysis performed by us with the use of interpretation technique approved on reservoirs of Zhuravsky-Vorobyevsky petroleum accumulation zone, as well as the core tests indicate the presence of oil-saturated reservoirs in the Paleocene sediments of Blagodarnenskaya structure.

Mathematical modeling of the acoustic and elastic anisotropy of the shale reservoir rocks of the Dnipro-Donetsk depression

The purpose of the work is to analyze the parameters of elastic and acoustic anisotropy in the study of a multicomponent reservoir rock model, which is represented by shale. Research theory To solve this problem, the methods of conditional moment functions using the Mori-Tanaka calculation scheme, as well as the ordinary least squares were used. The technique of effective elastic invariables mathematical modelling of unconventional shale reservoir rocks has been developed. Justification of the mathematical model Eight varieties of mathematical models that characterize the mineral composition, the structure of the void space and elastic properties that are characteristic for shale reservoir rocks of the Dnipro-Donetsk depression in Ukraine were substantiated and developed. The models are based on previous publications by the authors and the results of petrographic studies at the Institute of Geology. Results The authors for the first time carried out an analysis of elastic constant rock models, acoustic tensor components, linearity and shale parameters, isolines stereo projections of index surfaces of nine elastic anisotropy parameters, as well as Thomsen parameters. Acoustic data can be used to trace the change in the structure of the reservoir rock void space, the concentration of rock-forming minerals in the rock. Fracturing has a greater effect on rock structure than granular voids and mineral structure. The orientation of inclusions has the greatest influence on the coefficient of acoustic anisotropy, anisotropy coefficients in rocks, where the voids are oriented in the plane perpendicular to the borehole axis have the largest values (more than 20%). When calculating the Thomsen parameters, the parameters of elastic anisotropy were obtained. They characterize not only the mineral composition of the rocks but also the qualitative structure of the void space, the orientation of minerals and voids in the rocks. Thomsen parameters correlate with acoustic anisotropy parameters for shale reservoir models. The parameters of acoustic and elastic anisotropy are indicators in the studies of similar-type rocks with different types of mineral inclusions and the structure of the void space. The mathematical modelling of elastic and acoustic parameters which characterizes their anisotropy and was carried out by the authors is an important step in substantiating mathematical models of shale reservoir rocks. Such models can be used in the interpretation of geophysical data (seismic surveys and well logging) to make corrections for elastic anisotropy in prospecting and exploration of oil, gas and water saturated unconventional shale reservoir rocks of complex structure, and also to compile a database of mathematical models of reservoir rocks in the given region.

MUSCL scheme for Single Well Chemical Tracer Test simulation, design and interpretation

Our paper presents an improved numerical scheme to simulate Single Well Chemical Tracer Test (SWCTT) method. SWCTT is mainly applied to determine the residual oil saturation of reservoirs. It consists in injecting an aqueous slug of a primary tracer into the reservoir formation and displacing it at a certain distance from the well. This tracer is partly miscible with oil on the one hand, and generates in situ a secondary tracer on the other hand. As a consequence, a shift is observed between the primary and the secondary tracers arrival times when production is resumed. This time shift is used to evaluate the residual oil saturation. In our paper, we propose a numerical scheme based on a fractional time stepping technique to decouple the resolution of the phases mass conservation equations and the chemical tracers mole conservation equations. For the phases resolution, we use an implicit scheme to ensure stability and robustness. For the chemical tracers, we propose an explicit second-order scheme in time and in space via MUSCL technique to improve the tracers time-shift calculation. The proposed numerical method is implemented on a realistic simulation model consisting of a vertical well crossing a reservoir consisting of a stack of homogeneous layers. By reducing the numerical dispersion, the proposed scheme improves the accuracy of predicted concentration profiles, without significantly increasing the computation time. Finally, the advantages of using a second-order scheme for residual oil saturation assessment are discussed on the basis of a radial 1D mesh convergence study.

低饱和度油藏产水率测井预测技术研究

低饱和度油藏产水率测井预测技术研究