Pre-Caspian Basin Research Articles

Characteristics of the structure and hydrocarbon prospectivity of the deeply buried strata in the eastern Precaspian basin

The article examines the geological structure and oil and gas prospects of the pre-salt complex in the eastern Precaspian Basin (PB). Based on the synthesis and comprehensive analysis of geological exploration (GE) results and the analysis of geological-geochemical criteria for hydrocarbon potential, the oil and gas geological zoning has been updated, and effective directions for GE have been identified. The justification of a new hydrocarbon resources base within the eastern PB margin can be ensured by further investigating of the deeply buried Devonian-Middle Carboniferous horizons in the known petroleum plays, as well as within the less explored Sakmar-Kokpektinsky segment of the Ural fold-and-thrust belt. Within the productive KT-I and KT-II formations, there is an unrealized hydrocarbon potential at depths of 5-6 km. Using the example of the Bozoba West area, the oil and gas prospects of the Visean-Bashkirian and Lower Permian strata are examined, highlighting the significance of faults as elements of the hydrocarbon system. The applied set of 3D seismic survey data and deep drilling allowed for the interpretation of deep seismic sections, up to depths of 7.0-7.5 km. The Middle-Upper Devonian strata are considered prospective but have not been extensively explored by deep drilling. To establish a new hydrocarbon resource base within the eastern Precaspian Basin margin, it is recommended to conduct advanced regional seismic surveys and parametric exploration drilling.

Deep-Water Traction Current in Upper Carboniferous Stratigraphic Succession of Moscow Stage, Southeastern Pre-Caspian Basin

Deep-Water Traction Current in Upper Carboniferous Stratigraphic Succession of Moscow Stage, Southeastern Pre-Caspian Basin

Formation mechanical mechanism of low-angle fractures in pre-salt carbonate reservoirs: a case study from Carboniferous KT-I formation of the NT oilfield in the eastern margin of the Precaspian Basin, Kazakhstan

Fracture is an important factor that affects the oil and gas productivity of carbonate reservoirs. Much researches have been done on the origin of high-angle fractures in carbonate reservoirs, but few efforts have been made on the genetic mechanical mechanism of low-angle fractures. Based on the seismic data, core data, conventional logging data and rock mechanics experimental data, combined with three-dimensional in situ stress field simulation methods, the features, formation geological conditions and genetic mechanical mechanism of low-angle fractures (LAFs) were analyzed by applying Coulomb–Moore criterion, Griffith criterion and non-coordination criterion. The proportion of the number of shear fractures is as high as 90.2%, while that of tensile fractures is only 9.8% in the study area. Shear fractures are mainly unfilled fractures, and tensile fractures are mainly partially filled fractures. The LAFs were formed in the second tectonic movement, in which the knee-fold structure with high in the west and low in the east developed in the study area. The buried depth of most parts of the KT-I formation is 800 m when the study area develops the knee-fold structure, with a maximum depth of 1800 m and a minimum buried depth of 70 m, and the dip angle of the steepest part of the stratum is about 20°. A large number of LAFs were formed in the study area under the joint influence of tectonics and abnormally high pressure of water, including near-horizontal LAFs in the non-weak fabrics section (type I low-angle shear fractures), the LAFs having a certain angle with bedding in the non-weak fabrics section (type II low-angle shear fractures) and near-horizontal LAFs in the weak fabrics section (type III low-angle shear fractures). The formation of type I and type II low-angle shear fractures follows the Coulomb–Moore criterion. Type I low-angle shear fractures are formed in strata with a certain dip angle, while type II low-angle shear fractures are formed in near-horizontal strata. Type III low-angle shear fractures are formed under the comprehensive influence of pre-existing weak fabrics and strong horizontal extrusion, which follows the non-coordination criterion. Low-angle tensile fractures are mainly caused by abnormally high pressure and reverse faults in the study area, following Griffith’s criterion. The research in this paper not only reveals the formation mechanical mechanism of LAFs in pre-salt carbonate reservoirs but also provides guidance for the prediction of LAFs and solving the problem of water channeling caused by LAFs in oil fields.

PERSPECTIVES OF SEARCH FOR RAW HYDROCARBON AND SOLID MINERALS DEPOSITS IN THE EASTERN HALF OF PRECASPIAN DEPRESSION (AKSAI – NORTH MAKAT AREA)

The possibility of identifying deep and ultra-deep raw hydrocarbon deposits and also the deposits of solid minerals in eastern part of Precaspian basin within Aksai-Northern Makat section totaling 70,000 sq.km. has been studied on the basis of the analysis of isodata, geological, tectonic, geophysical maps, mineral resources maps, specialized mineragenic studies, as well as new ideas on geodynamic development of Kazakhstan and, most crucial, taking into account theoretical and practical ideas about origin of abiogenic raw hydrocarbon deposits associated with formation of volcanic hydrogen, referring to the deliverables of gravity study and prospecting work, primarily magnetic prospecting. At the same time, a keen attention has been paid to the deep structure and morphology of Precaspian rift, providing significant impact on the deposits` formation. The analysis resulted with identification of, for the first time ever, several highly promising magnetic anomalies where new shallow, medium and deep petroleum and gas deposits may concentrate, including potential deposits of ferrous, non-ferrous, rare, rare earth and radioactive metals. A considerable effort has also been made to the perspectives of search for oil shale and light tight oil which are potential sources for multiple augmentation of the reserves of natural raw hydrocarbons.

A REVIEW OF ENHANCED OIL RECOVERY METHODS USED IN THE FIELDS OF KAZAKHSTAN

Application of enhanced oil recovery methods in Kazakhstan has been ongoing for decades alongside the continued discovery of new oil and gas fields in the Pre-Caspian Basin. The objective of this review is to provide an overview of the hydrocarbon reserves and production, and the status of the petroleum industry in Kazakhstan, with a focus on the EOR methods and projects being applied to recover those reserves. A summary of the specific EOR methods in use was prepared, and existing enhanced recovery projects in Kazakhstan were reviewed and their successes and challenges were investigated. The performance of these projects in the context of EOR performance indicators such as capillary number and mobility ratio, as well as operational and environmental issues, were examined. Recommendations for current and potential applications of EOR in Kazakhstan were also discussed. The widespread application of thermal EOR methods, in use for decades in Kazakhstan’s older fields, was found to be successful, with very favorable impacts on mobility ratio from the addition of thermal energy to the reservoirs. Miscible EOR methods in Kazakhstan have had more limited success, with some significant challenges due to high concentration of hydrogen sulfide in the injected gas. Polymer injection started in the late 1960s, achieving good results. A recent polymer injection pilot project has shown some promise, with a favorable impact on mobility ratio and oil production, although the project has not yet been expanded beyond two polymer injectors. These results indicate the huge potential of existing and future EOR projects. This review is the first compilation of Kazakhstan’s existing oil and gas reserves, production, and EOR project performance, and should be seen as a guide to the existing applications of EOR methods in Kazakhstan.

Morphology and Depositional Processes of a Carbonate-Filled Canyon in the Carboniferous KT-II Formation of the Eastern Precaspian Basin, Kazakhstan: Insight from 3D Seismic Data

Canyons in carbonate depositional settings, as important elements of the source-to-sink system, remain poorly studied compared to those in siliciclastic depositional environments. The latest high-resolution three-dimensional seismic data, well logs, and core data at the eastern edge of the Precaspian Basin are used to investigate the geomorphology, infillings, and depositional process of a unique carbonate-filled canyon in the Carboniferous KT-II formation parallel to the carbonate platform, which is distinct from other slope-perpendicular canyons. The canyon has a total length of more than 52.3 km with a nearly N-S orientation and an S-shaped geometry, and the whole canyon can be divided into three segments by two knickpoints. The slope-parallel orientation of the canyon is mainly controlled by the palaeogeomorphology and reverse faults. Due to the collision of the Kazakh and European plates in the early-middle Visean (early Carboniferous), the canyon was formed in a northern tilted, elongated, and restricted palaeotopographic feature between uplifts. The development of reverse faults related to tectonic movement controlled the variations in the width of the canyon and the positions of the knickpoints. Tectonics controlled the orientation and formation of the canyon, while sedimentary processes contributed to its infilling. The well-seismic tie analysis indicated two distinct periods of the canyon fillings, Ss1 and Ss2, which were separated by a second-order sequence boundary. The lower part contained sediments supplied by both sides of the canyon through channels or gullies, and the upper part was dominated by a carbonate platform that prograded from the eastern side of the canyon. The evolution of the canyon can be subdivided into three stages. The increasing stage was mainly characterized by significant upslope erosion through headward retrogressive mass failures in the slope-parallel confined negative relief to form the canyon during the lowstand system tract of Ss1. Subsequently, in the early filling stage, the carbonate factory was productive during the highstand, and massive excess carbonate sediments were transported into the adjacent canyon by channels or gullies on both sides and deposited. The canyon was basically filled, and the morphology became much gentler. During the subsequent late filling stage, the carbonate platform was flooded again during the highstand, and the production rates of the carbonate factory greatly increased. The lateral progradation of carbonate platforms accelerated on the canyon of the early filling stage and further into the inner sag.

Reactive Transport Modeling and Sensitivity Analysis of CO2–Rock–Brine Interactions at Ebeity Reservoir, West Kazakhstan

This study investigated the reactive transport modeling of CO2 injection into the Kazakhstan reservoir to identify mineralogical and porosity changes due to geochemical reactions. Additionally, sensitivity analysis was performed to test the effect of the surface area and gas impurity on the CO2 storage capability. Despite the current need to investigate carbon sequestration in Kazakhstan, a limited number of studies have been conducted in this field. The Ebeity oil reservoir sandstone formation in the Pre-Caspian Basin has been tested as a potential CO2 storage site. The 1D PHREEQC simulation results of 10,000 years suggest that reservoirs with a higher abundance of these secondary carbonates may be better suited for long-term CO2 sequestration. The concentration of Fe3+ fluctuated, influenced by magnetite and siderite dissolution, leading to ankerite precipitation at 20 and 40 m. The porosity increased from 15% to 18.2% at 1 m and 20 m, favoring a higher CO2 storage capacity, while at 40 m, it remained stable due to minor mineral alterations. A reduced surface area significantly limits the formation of dawsonite, a crucial secondary mineral for CO2 trapping. For instance, at λ = 0.001, dawsonite formation dropped to 6 mol/kgw compared to 24 mol/kgw at λ = 1. Overall, the results of this study can play an essential role in future geological analyses to develop CO2 storage in Kazakhstan for nearby reservoirs with similar geological characteristics.

A rapid optimization methodology of produced gas reinjection EOR in carbonate reservoirs

The Carboniferous carbonate reservoir of the Pre-Caspian basin has abundant oil and gas resources. The typical features of low porosity and low permeability and reservoir oil with high concentrations of H2S and CO2 and heavily dissolved gas-oil ratio allow produced gas reinjection as an effective and economic way to enhance oil recovery (EOR). However, the optimal design of injection/production parameters for gas injection processes is the premise for development scheme and technical decision. Compared to the conventional method of one-parameter-at-a-time approach with lack of interactions between various factors and tremendous challenge of main controlling factors identified, in this work we present a rapid optimization methodology to identify the main factors from numerous candidate parameters and obtain optimum levels of key factors. Our chosen methodology is a combination of experimental design with response surface method (RSM). Firstly, the two-level Plackett-Burman experimental design was used to screen and rank ten operational variables for the gas reinjection process. The top five significant parameters with the sum of their influencing weight greater than 94.3 % are bottomhole pressure for producers, reinjection ratio, injection period, injection gas timing and completion interval. Then the three-level Box-Behnken experimental design was employed to perform optimization exploration with the RSM. Regression models of the oil recovery factor (RF) were constructed by using these five key factors, which fits excellently with numerical simulation results. Finally, the optimal levels of controlling factors were determined to maximize oil recovery. This optimization procedure is very practical for reservoir engineers to guide a rapid evaluation of gas injection processes.

MICROFACIES AND GEOCHEMICAL CHARACTERISTICSOF THE UPPER DEVONIAN KT-III CARBONATE, EASTERN EDGE OF PRECASPIAN BASIN

Deeply buried Devonian sediments of the eastern edge of Precaspian Basin are widely extended; Upper Devonian reef-like deposits can be identified according to seismic surveys and poorly characterized by core material. In the present study depositional environment, predominant biota and diagenetic characteristics of the KT-III carbonate formation are described in order to evaluate reservoir potential. The paper presents the results of determining the mineral composition, geochemical features, sedimentological (identification and description of microfacies) and diagenetic characteristics of the Upper Devonian carbonate sediments of the Urikhtau area (KT-III).

Evaluation of pore-throat structures of carbonate reservoirs based on petrophysical facies division

After complex geological transformation, such as sedimentation, diagenesis, and tectonic transformation, carbonate reservoirs have developed multiple reservoir spaces with significant heterogeneity and various pore-throat structures, including pores, vugs, and fractures. Due to these characteristics, many problems have been caused during the development of carbonate reservoirs, such as large differences between the initial production capacities of single wells and serious water channeling after injection, which have brought many challenges to the efficient development of carbonate reservoirs. Therefore, based on a reservoir evaluation method of petrophysical facies, this study classified and evaluated the pore-throat structures of Carboniferous carbonate reservoirs in the North Truwa oilfield of the Pre-Caspian Basin. Based on the data of the core, thin section, scanning electron microscope, high-pressure mercury injection, sedimentary facies, diagenetic facies, and the development of fractures and karst vugs, six reservoir petrophysical facies in the study area were classified and named, including the facies of favorable sedimentation-constructive diagenesis-fracture and vug, the facies of favorable sedimentation-constructive diagenesis-non-fracture or vug, the facies of favorable sedimentation-destructive diagenesis-fracture and vug, the facies of favorable sedimentation-destructive diagenesis-non-fracture or vug, the facies of unfavorable sedimentation-constructive diagenesis-non-fracture or vug, and the facies of unfavorable sedimentation-destructive diagenesis-non-fracture or vug. The recognition and division of diagenetic facies were based on the K-nearest neighbor. Four quantitative parameters were also selected to characterize the pore-throat structures, including displacement pressure (Pd), mercury removal efficiency (Em), median throat radius (R50), and sorting coefficient (Cs). Based on the principal component analysis, the classification and evaluation standards of pore-throat structures in different petrophysical facies were established. Combined with the flow profile measured by production logging tools, the relationship between different petrophysical facies and productions was also revealed. As a result, this study can provide suggestions for the adjustment strategy of water-driven production, which lays an important foundation for the fine development of carbonate reservoirs.

INFLUENCE OF THE EVAPORITE FORMATION STRUCTURE ON SALT TECTONICS AND HYDROCARBON TRAPS (BY THE RESULTS OF NUMERICAL SIMULATION OF HALOKINESIS IN THE PRE-CASPIAN)

Within the Pre-Caspian sedimentary basin, there is certain regularity in the distribution of types of structures of salt tectonics. It is characterized by concentric zoning corresponding to the change in the sedimentation thickness of the evaporite sequence. As it increases from 0 to 6 km towards the center of the basin, stamp (embryonic) salt uplifts are replaced by salt pillows first and then by salt domes and diapirs, finally changing to salt massifs and amoeboid-shaped salt ridges. In addition, diapirs in the sections of the Pre-Caspian basin, drawn from the drilling and seismic data, are shaped like high-amplitude "fingers" with a flat base, which is not a typical picture of the Rayleigh – Taylor instability development. Since halokinesis is the main factor controlling the migration and accumulation of hydrocarbons in the Preaspian region, background and aim of prospecting and exploration require identifying the specifics of the formation of various types of salt structures and the relationship between their location patterns and halokinesis process.Numerical simulation shows that, depending on the instable layer thickness and its relationship with the total thickness of the overlying layers, the instability development occurs at different rates, forming different types of structures. When the thickness of the instable layer is greater than or comparable to the thickness of the denser overburden, there occur the salt masses. A greater thickness of the overlying layer gives rise to the formation of classical mushroom-shaped diapirs. A small-thickness low-density layer first undergoes a full bending as it rises, so that its top and bottom turn out to be morphologically similar to each other, thus giving a misleading impression of ordinary stamp folds. Somewhat greater thickness of the low-density layer leads to the development of "pillows" therein. Detailed modeling made it possible to relate the specific shape of the Pre-Caspian diapirs to the fact that the basal and top horizons of the evaporite formation, being composed mainly of terrigenous, carbonate and sulfate rocks, have a normal, non-inverse density and mask complex diapiric structures of halite-saturated domal cores.

Application of Seismic Waveform Indicator Inversion in the Depth Domain: A Case Study of Pre-Salt Thin Carbonate Reservoir Prediction

Prestack depth-migrated seismic data, having more accurate imaging position and amplitude fidelity than prestack time-migrated seismic data, are supposed to produce a higher quality reservoir prediction result by using depth-domain inversion. Some researchers have developed different methods of depth-domain seismic inversion. However, it has not been widely used in the industry probably because of two reasons: (1) it is a complex process to conduct depth-domain seismic inversion due to the nonstationary depth-domain seismic wavelet; and (2) time-domain seismic inversion is considered capable of solving the problem with less cost, both in regard to time and the economy. In this paper, we try to use the seismic waveform indicator inversion method in the depth domain. First, a forward model was built to demonstrate that seismic waveforms both in the time domain and the depth domain are highly correlated with lithologic associations. Second, a quantitative evaluation method of seismic data for reservoir prediction was proposed, which can help geophysicists estimate time-domain and depth-domain inversion effects before inversion. Finally, the seismic waveform indicator inversion method was implemented for presalt thin carbonate reservoir prediction in the Central Block at the eastern margin of the Pre-Caspian Basin. The depth-domain inversion result shows a relatively true structure and higher resolution validated by wells.

The Late Devonian contraction along the Precaspian Basin north margin: Transpressional range building in the intracratonic domain

The evolution of intraplate sedimentary basins located in the vicinity of an active convergent plate boundary is often controlled by the collisional dynamics of the adjacent orogen. The transfer of compression from the orogen to the platform's interior results in the formation of complex structural geometry and kinematics that often reactivate older crustal faults, focus far-field stresses and control the evolution of associated sedimentary basins. One place where this localisation can be optimally understood is the Precaspian Basin, situated at the SE periphery of the East European Craton and bordered to the east by the Uralian orogen. The Precaspian Basin and its northern margin experienced long-term extension and subsidence interrupted by several short-lived shortening episodes. To understand the impact and role of pre-existing basement structures on the geometry and kinematics of the subsequent deformation, we analysed subsurface data from the northern margin of the Precaspian Basin by the means of 3D seismic interpretation correlated with wells and structural modelling. The analysis results provide new insights into the kinematic effects of the Late Devonian contraction event. The superposition of stratigraphic units above and below the angular unconformity suggests an intra-Famennian age of the deformation event. Steeply dipping bi-verging reverse fault zones associated with variable amounts of sinistral strike-slip movement component display an arcuate geometry, trending from WSW-ENE to NW-SE. The distribution of deformation indicates that this complex kinematic pattern was driven by a NE-SW oriented contraction and transpression, where faults show the characteristics of a restraining bend area. This area is interpreted as part of a regional transcurrent fault system developed on the northern periphery of the Precaspian Basin. Furthermore, the study results suggest that intralithospheric stress localisation transmitted by the Paleouralian subduction zone resulted in the reactivation of pre-existing basement structures, propagation of faults, and localized short-term exhumation of the Precaspian Basin north margin. Generated by the collision of Magnitogorsk volcanic arc with East European Craton, far-field stress transfer produced a zone of oblique deformation. These data and interpretation demonstrate that the northern margin of the Precaspian Basin is an excellent natural setting to investigate and better understand mechanisms of far-field strain localisation and reactivation of deformational structures in stable platform areas resulting in the intracratonic mountain building process.

GEOCHEMICAL CHARACTERISTICS OF THE DOMANIKOID-TYPE LATE DEVONIAN STRATA OF THE KOBLANDY-TAMDY UPLIFT

The article presents the lithological and geochemical characteristics of the Upper Devonian sediments of the Koblandy structure in the northeastern part of the Precaspian Basin. Based on the core data from the Koblandy-3 well from the Upper Devonian strata of the presalt complex, the results of RockEval and isotopic analysis are presented. Intervals of kerogen-siliceous-carbonate rocks enriched in organic matter have been established, which, according to a complex of microand macrocharacteristics, can be attributed to domanikoid-type sediments. The Domanikoid highcarbon formation of the neighboring Volga-Ural Basin is an effective source rock. The generative potential of the established domanikoid-type sediments of the Koblandy-3 well is characterized by high TOC values of 0.1-5.7%, the Production Index (PI) varies from 0.1-0.3, which corresponds to the oil window. Three lithotypes of domanikoid-type sediments deposited in predominantly deep marine environment have been established. The association of potential reef bodies in the vicinity of domanikoid-type source rocks indicate in favor of petroleum system within the upper Devonian presalt complex of the Koblandy-Tamdy uplift zone

ASSESSMENT OF OIL AND GAS POTENTIAL IN PRIMORSKAYA ZONE OF CARBONATE UPLIFT OF SOUTHERN PRECASPIAN SEDIMENTARY BASIN

The results of lithofacies studies and paleogeographic reconstructions of the Late DevonianEarly Visean stage and stratigraphic evolution of the Primorskaya zone of uplifts in the south of Precaspian Basin are presented. The complex geological structure of the region is mainly due to the influence of tectonic, volcanic and denudation processes on sedimentation. The spatial distribution of carbonate accumulations in the Primorskaya zone of the Precaspian Basin is determined by the different duration of sedimentation stages and the block structure of the basement. The results of the deep wells drilled in the recent years have made it possible to refine the internal geological structure, justification of new exploration objects in the Late Devonian strata and reevaluate the oil and gas potential and petroleum resources in the south of the Precaspian depression. After recent exploration works, the geological model for the onshore prospective structure traps has been improved, additionally prospective exploration objects have been predicted in the shelf of the Caspian Sea. The most of potential petroleum resources of the Primorskaya zone is the resources of the new offshore exploration objects in Caspian Sea. Non-structural traps can accumulate gigantic hydrocarbon volumes. This is a new highly prospective hydrocarbon exploration direction in the Precaspian Basin

PROSPECTS OF OIL AND GAS POTENTIAL OF THE JUNCTION ZONE OF THE NORTH-EAST OF THE PRECASPIAN BASIN AND THE SOUTHERN SEGMENT OF THE URAL FOLD SYSTEM (AKTOBE URALIAN FOREDEEP)

The identification of promising areas of exploration to develop the resource base of the Aktobe region is an urgent issue due to the gradual depletion of proven hydrocarbon reserves. The subsalt complex of the Aktobe Uralian Foreland is a prospective object, where prospecting and exploration work was carried out unevenly in the 1950s and 1980s, and most of the seismic survey data of 2004-2008 are low-informative. The subsalt complex of the studied area has been poorly studied by high resolution seismic studies and deep exploration drilling and previously belonged to the territories with low hydrocarbon potential. On the basis of the conducted research, data on the structural and tectonic zoning of the junction zone of the Precaspian basin and the southern segment of the Urals Foredeep are summarized, the geological structure of the Aktobe Uralian Foreland area is substantiated, favorable geochemical criteria of oil and gas potential are revealed.

Salt diapirism in the eastern margin of the Pre-Caspian Basin: Insight from physical experiments

Since the 1950 s, salt diapirism has been shown to be closely related to hydrocarbon accumulation and has been a hot spot of research activity in structural and petroleum geology. Many salt structural, such as salt wall, roller, pillow, welt and anticline have been formed in the Pre-Caspian Basin during the post-Kungurian (Lower Permian) times. Meanwhile, mechanisms of salt structure deformation and the influence of the sub-salt strata on salt diapirism is still unclear. Based on seismic data and a geological model of the eastern margin of the Pre-Caspian Basin, physical simulation experiments of salt diapirism have been conceived. Performed to analyze, the dynamic process of salt structure deformation, and to clarify mechanisms of the salt diapirism and the relationships between the salt structures and the underlying strata. Differential loading seems to a principal mechanism accounting for sediment. The sedimentation rate of the overburden formations had a great impact on the salt structure forms and geometry. The physical experiments showed that: salt diapirism starts in the basin margin with progradation of sediments and then continues down-slope toward the basin center. The height and width of the salt structures are influenced by dip angle of the sub-salt. The larger-scale salt structures occurred in the inner basin zones, followed the central slope zone and the basin margin with a large dip angle.

Geodynamic hazards and risk assessment at the Karachaganak oil, gas, and condensate field

The geodynamic hazards and risk assessment at the Karachaganak oil, gas, and condensate field (KOGCF) were explored on the northern board of the Pre-Caspian Basin to predict the consequences of the long-term exploitation of this field. We integrate multiple measurements, including repeated accurate leveling, Global Positioning System (GPS) measurements, and high precision gravimetric and seismological monitoring at the KOGCF. The results of geodynamic monitoring at the KOGCF for the first time made it possible to prove noticeable seismic deformation processes in the sedimentary cover under the influence of hydrocarbon production. The vertical displacements and horizontal movement along faults, changes in local gravity anomalies, and earthquake sources at depths comparable to hydrocarbon production intervals at the KOGCF have been identified. The maximum amplitudes of modern vertical movement of the earth's surface and the minimum values of the differently oriented horizontal movement were revealed within the projection on the ground surface of the crest of the carbonate massif (Upper Devonian-Lower Permian age). The results suggest the expansion of uneven compression in the crest of the KOGCF while tension processes occur on its periphery. There is a decrease in gravity variations in relation to the slopes of this massif in areas with active hydrocarbon production. An extended zone of high-gradient steps of ΔGa anomalies, spatially coinciding with the position of fault zones, is mapped along the periphery of the contour of production wells. In the northeastern part of the KOGCF, seismic events were registered practically in the depth intervals of the productive horizons from which hydrocarbons are produced. A spatial relationship between the seismic events and the anomalous deformation activity in the northeast KOGCF has been revealed. Consequently, the field development has provoked both intense deformation of the earth's surface and weak local seismicity.

Fractal Characteristics of Pore-Throats Structure and Quality Evaluation of Carbonate Reservoirs in Eastern Margin of Pre-Caspian Basin

The Carboniferous reservoir KT-II layer in the Eastern margin of the Pre-Caspian Basin was formed in the open platform sedimentary environment and marked by a complicated pore-throats structure. Understanding the main controls on the carbonate reservoir quality is of great significance for reservoir classification and a relevant production prediction. This study focuses on revealing reservoir pore-throats structure’s fractal characteristics by analyzing the mercury intrusion capillary pressure (MICP), with the integration of the pore-throats radius’ distribution data. The relationship between fractal dimensions and reservoir parameters such as physical properties, mercury median saturation pressure (Pc50) and the proportion of large-size (radius > 0.1 μm) pores demonstrate that the lower fractal dimension corresponds not only to core plug samples with higher permeability, but also to lower Pc50 and a higher proportion of large pore-throats. Three classes of carbonate reservoir with different qualities were defined according to their fractal dimensions, petrophysical properties and photomicrograph features, et al. Combined with flow profiles from Production Log Tool tests, the relationship between the carbonate reservoir type and production behavior was revealed, thus providing suggestions on the middle and late stage of the water flooding production adjustment strategy. This work provides a typical case study for the further comprehensive evaluation and classification of a carbonate reservoir and it is quite meaningful for production efficiency optimization.

POTENTIAL SOURCE ROCKS EVALUATION FOR THE PRE-SALT COMPLEX OF THE EASTERN EDGE OF PRECASPIAN BASIN

Through basin analysis, the major tectonic stages and paleogeographic conditions of the formation of potential oil and gas source rocks of the subsalt complex of the eastern side zone of the Precaspian basin are considered. Prediction and localization of potential source rocks is critical for the Precaspian petroleum system understanding, both during petroleum play assessment at the prospecting and exploration stages. The generation and emigration potential of the oil and gas basin is determined not only by the concentration of the initial organic matter in the rock, but also by the type of kerogen. Based on Rock-Eval studies and comparative analysis with published biomarker data, the generation potential, genetic type and thermal maturity are analyzed depending on the age and structural relatedness of potential source rocks. A high generation potential has been established for the Lower Permian deposits, the occurrence of multiple generation foci controlled by the type and concentration of organic matter is predicted, which led to the formation of specific reservoirs of the "akzharite" type. The generation potential of the Visean-Bashkirian deposits is poor to average, catagenetic unconformities have been established within KT-II, KT-I, which indicates erosions, the total organic carbon (TOC) is 0.1-4%, the hydrogen index increases with depth, for samples enriched with TOC and with a content of S2 > 1, type II kerogen has been established, which it is an indicator of reducing marine environment. 2D basin modeling was performed in order to reconstruct the thermal evolution of potential source rocks and their thermal maturity and transformation ratio were modelled to determine the regional characteristics of hydrocarbon generation and migration. It is assumed that the formation and distribution area of the primary source rocks is associated with reducing conditions of the deep-sea shelf and continental slope and intensive subsidence in the Late Devonian-Lower Permian times. Conducting a comprehensive analysis of paleogeographic and paleotectonic conditions for the formation of potential source rocks is of key importance in the seismic interpretation and reconstruction of thermal history. 2D basin modeling was performed in order to reconstruct the thermal history of potential oil-producing strata and the degree of catagenetic maturity and the kerogen maturity index were estimated to determine the regional characteristics of hydrocarbon generation and migration.