Pre-Caspian Basin Research Articles

Prospect evaluation based on integrated petroleum system analysis: Block E case study, south-eastern edge of Precaspian Basin (Kazakhstan)

Generative potential and thermal maturity for Upper Palaeozoic source rocks from the south-eastern edge of Precaspian Basin were determined using Rock–Eval. A high hydrocarbon source rock generative potential and high degree of thermal maturity for the Lower Permian, Mid-Carboniferous strata have been revealed based on 39 rock samples. TOC values of 0.4–5.5% have been obtained for mature source rocks. Integrated geochemical analysis determined from Rock–Eval studies combined with 1D basin modelling was utilized in order to reconstruct thermal evolution for the Upper Palaeozoic source rocks. Calibrated 1D models for three wells had been constructed to understand petroleum system. For two deep exploration wells (Nur-1 and Tassym SE-1), which penetrated pre-salt strata at the depths of 5.7 and 7 km, respectively, the impact of salt diapirism on timing of maturation was modelled. Type II kerogen was used, which is based on previous palaeogeographic studies. The stratigraphic framework and major stages of geodynamic evolution were analysed. Salt-related structural traps in post-salt strata have been described based on 3D seismic data, and additional intra-salt sediment packages have been delineated. Discovered producing oil fields in the Upper Triassic and Jurassic–Cretaceous stratigraphic sections are mainly confined to the four-way dip structural closures above the steep flanks of salt structures. Based on burial and thermal modelling, the maturation and generation behaviour of kerogen Type II below salt-related minibasins and close to thick salt diapirs were inferred. For Lower Permian SR with type II kerogen, the generation peak (maturity over 50%) occurs in Middle to Late Jurassic. For predominantly carbonate and terrigenous-carbonate Mid-Carboniferous marine SR, generation peak occurs earlier below salt withdrawal minibasins. Implications for deeper hydrocarbon prospectivity were made for the study area, and methodology for evaluating hydrocarbon potential adopting 1D basin modelling technique and geochemical data is presented.

Geochemical studies of gases from oil and gas fields in the southern part of the caspian basin and their correlation with the results of oil geochemistry

This article presents the results and interpretation of the compositional and isotopic analysis of carbon in 14 gas samples derived from oil and gas fields and structures (Liman, East Makat, North Kotyrtas, Zholamanov, S. Nurzhanov and West Prorva) of the southern part of Pre-Caspian basin. According to the results of this study, all gases have a thermogenic source and their organic matters were deposited in the marine environment, which is also consistent with the results of biomarker analysis of oils from these studied fields. A sharp enrichment of propane with heavy carbon isotope in gas №55 of East Makat field suggests its biodegradation, which is also confirmed by the results of gas chromatographic analysis of oil from this well. A star diagram of gases was plotted based on normalized values of carbon isotopic composition of C1-C5, according to the results of which the studied samples can be divided into 5 genetically different groups. The identified groups based on results of this gas analysis are also consistent with the results of «fingerprinting» of oil from these fields. Keywords: gas composition; gas isotopic composition; Rayleigh fractionation; Bernard diagram; Clayton diagram; Laurent diagram; Chung diagram; enrichment in heavy isotope.

Lithological and facial features of organogenic structures of the second carbonate stratum of the eastern flang of the Pre-Caspian depression on Zharkamys uplift

The Pre-Caspian Basin is the major oil and gas basin in Kazakhstan. It contains huge hydrocarbon reserves within pre-salt carbonate deposits. There had been numerous discoveries of oil and gas-condensate fields associated with pre-salt carbonate complexes in the Eastern part of the Caspian Basin.
 The object of this study is the second carbonate stratum (CS-II) of the Late Visean Early Moskovian age of the Eastern part of the Pre-Caspian Basin. The formation of the Eastern part of the Pre-Caspian Basin took place in the zone of the junction of the East European craton and folded structures of the Urals. These conditions predetermined the complexity of sedimentation processes, variety of lithological types of rocks and diagenesis processes with the formation of reservoir heterogeneity.
 CS-II will retain the leading role as the main reservoir of hydrocarbons and it has further potential for oil exploration in the region for two to three decades. It has been proven by the discovery of large oil and gas-condensate fields in the CS-II, such as Zhanazhol, Urikhtau, Kozhasai, Alibekmola, etc.

Reservoir Simulation of CO2 Storage Using Compositional Flow Model for Geological Formations in Frio Field and Precaspian Basin

CO2 storage is a greenhouse gas mitigation instrument for many countries. In this paper, we investigate the possibility of CO2 storage in the region of the Precaspian basin using the compositional flow model that was verified by the data of the Frio pilot project, USA. We use local grid refinement in the commercial reservoir simulator. In the reservoir simulation for data of the Frio Pilot project, we have achieved a good history matching of well pressure. Different scenarios were tested, and post-injection migration was shown for both case studies. The long-term reservoir simulation shows the potential amount of trapped CO2 by residual and dissolved trapping mechanisms in the Precaspian basin. The performed uncertainty study covered the uncertainty of the model’s parameters resulting in P10, P50 and P90 cases in terms of the amount of trapped CO2.

Lower Visean sea-level changes in the northern Precaspian Basin

This study presents the sequence stratigraphic interpretation of subsurface data in a Lower Carboniferous lagoon setting in the northern boundary zone of the Precaspian Basin. The proposed stratigraphic and facies distribution model of the lagoon fill enables the reconstruction of the relative sea-level history and refines the understanding of the geological evolution and eustatic changes in the Caspi region during the Lower Carboniferous. Semi-circular carbonate mounds were built in the Devonian period and Tournaisian stage enclosing a lagoon with an opening towards the Caspi Sea in a southeast direction. A sea-level fall at the end of the Tournaisian stage terminated the growth of the carbonate buildups; during the Lower Visean (Lower Carboniferous) time, the lagoon was filled with mixed siliciclastic and carbonate sediments. The lagoon fill is interpreted as a third-order composite sequence composed of three fourth-order sequences representing sea-level changes with an increased magnitude and frequency relative to the quiet conditions that prevailed during the previous carbonate buildup in Famennian-Tournaisian. The highstand systems tracts of the fourth-order sequences are likely Waulsortian-type carbonate banks, while the falling-stage and lowstand systems tracts are mostly clastic progradational wedges. The transgressive systems tracts include retrograding shale and grain shoal facies. A prominent falling-stage systems tract was detected in the third fourth-order sequence in the lagoon fill representing a significant sea-level fall in lower Visean time. The falling-stage systems tract is composed of three downstepping-prograding lobes indicating a continuously falling sea level punctuated by minor pauses. Seismic imaging revealed a series of distinct prograding wedges inside the falling stage lobes that are either accretionary bedset or high-frequency nested sequences. The observed fall in sea level during the Lower Visean may be associated with, and it may provide stratigraphic evidence for the beginning of Paleozoic glaciation on Gondwana.

Influence of the Component Composition of Adsorbed Oil on the Microstructural Wettability of Hydrocarbon Reservoirs

The physicochemical mechanism of the development of microstructural wettability in oil and gas reservoirs is experimentally justified. It is shown that this mechanism is associated with the formation of mosaic hydrophobic areas on the interstitial surface of the reservoir rocks. It was revealed that hydrophobic areas are formed due to the competition of adsorption processes between aromatic and aliphatic structures. For example, the relationships between the hydrophobization index (the ratio of the hydrophobic interstitial surface to the total pore surface) and adsorbed oil composition were identified by studying core samples of carbonate rocks from the Karachaganak oil and gas condensate field (Kazakhstan) and the Astrakhan gas condensate field (southwestern part of the pre-Caspian Basin, Russia). The spectral coefficients characterizing the relative contribution of certain hydrocarbons to the adsorbed oil composition were determined using infrared spectroscopy. The dependences of microstructural wettability on the spectral coefficients are experimentally established. It is shown that the composition of adsorbed oil has a multidirectional effect on microstructural wettability. The presence of aromatic, oxidized, and sulfurized structures increases the hydrophobization index, whereas the presence of aliphatic and branched structures leads to its reduction. The closest relationship was noted between the microstructural wettability and the spectral coefficient that characterizes the presence of aromatic structures in the adsorbed oil.

Structure and Density of Sedimentary Basins in the Southern Part of the East-European Platform and Surrounding Area

Modern satellite gravity missions and ground gravimetry provide operational data models that can be used in various studies in geology, tectonics, and climatology, etc. In the present study, sedimentary basins in the southern part of the East European Platform and adjoining areas including the Caucasus are studied by employing the approach based on decompensative gravity anomalies. The new model of sediments, implying their thickness and density, demonstrates several important features of the sedimentary cover, which were not or differently imaged by previous studies. We found a significant redistribution of the low-dense sediments in the Black Sea. Another principal feature is the increased thickness of relatively low-dense sediments in the Eastern Greater Caucasus. The deepest part of the South Caspian basin is shifted to the north, close to the Apsheron Trough. In its present position, it is almost joined with the Terek–Caspian depression, which depth is also increased. The thickness of sediments is significantly decreased in the eastern Pre-Caspian basin. Therefore, the new sedimentary cover model gives a more detailed description of its thickness and density, reveals new features and helps in better understanding of the evolution of the basins, providing a background for further detailed studies of the region.

The Origin Analysis of “reversal foreset” of Late Carboniferous MKT Formation in Central Block of Pre-caspian Basin

The configuration of “reversal foreset”, which is a common geologic sedimentary phenomenon in seismic exploration, has been fully understood on its mechanism. In central block of pre-caspian Basin, a series of NE “reversal foreset” configurations were found. This kind of reflection is completely opposite to the paleogeomorphology which is high in the west and low in the east. It is difficult to clarify the origin mechanism of the “reversal foreset” configuration without sufficient data and understanding of regional tectonic evolution. Interpretations provided by previous studies did not reach a consensus understanding of the tectonic and sedimentary structures in the area. In this paper, based on well and regional data, the previous interpretations are analyzed, and the idea is put forward that the “reversal foreset” configuration represents superimposed retrogradation bodies developed in the process of rapid water flooding, and its formation is controlled by three factors -- “weak supply of single source”, “rapid transgression (weak source supply)” and “low and gentle depositional slope”. This recognition helps understanding the sedimentary evolution characteristics of the Late Carboniferous MKT formation in central block of Pre-caspian basin and promotes the later exploration of lithologic reservoir.

CO2 storage potential in sedimentary basins of Kazakhstan

The terms of the Paris Agreement oblige Kazakhstan to decrease its Greenhouse Gas (GHG) emissions by 2030. Annual GHG emissions of the country already went beyond the limit set by the Paris agreement in 2014 and this number is expected to increase with a growing economy showing that current measures of GHG mitigation in the country are insufficient. Despite the energy sector of the country being heavily dependent on its coal and substantial land resources, CCS was not featured in the “Green Economy” plan of the country. To investigate the applicability of this technology, six selected Kazakhstan sedimentary basins (the Precaspian, Mangyshlak, South-Torgay, Ustyurt, Chu-Sarysu, and Zaysan basins) were evaluated and ranked for geologic CO2 storage deployment in terms of containment, capacity, and feasibility. The effective CO2 storage capacities in oil reservoirs, gas reservoirs, and saline aquifers were estimated for each basin using the Carbon Sequestration Leadership Forum (CSLF) and USDOE methods. The evaluations revealed that the Precaspian Basin is the most suitable for geological CO2 storage, followed by the Mangyshlak, South Torgay, and Ustyurt basins. The total effective CO2 storage capacity of the country is estimated to be ∼583 Gt, of which ∼539 Gt corresponds to the abovementioned four suitable basins where most of injected CO2 is expected to be stored in the hydrodynamic traps. The results suggest that four sedimentary basins identified in this study have prospectivity to reduce GHG emissions of Kazakhstan significantly and thus enable the decarbonization of national economy to achieve the goals set by the Paris Agreement.

Pore-throat structure characteristics and its impact on the porosity and permeability relationship of Carboniferous carbonate reservoirs in eastern edge of Pre-Caspian Basin

Abstract Carboniferous carbonate reservoirs at the eastern edge of the Pre-Caspian Basin have undergone complex sedimentation, diagenesis and tectonism processes, and developed various reservoir space types of pores, cavities and fractures with complicated combination patterns which create intricate pore-throats structure. The complex pore-throat structure leads to the complex porosity-permeability relationship, bringing great challenges for classification and evaluation of reservoirs and efficient development. Based on the comprehensive analysis on cores, thin sections, SEM, mercury intrusion, routine core analysis and various tests, this paper systematically investigated the features and main controlling factors of pore-throats structure and its impact on the porosity-permeability relationship of the four reservoir types which were pore-cavity-fracture, pore-cavity, pore-fracture and pore, and three progresses are made. (1) A set of classification and descriptive approach for pore-throat structure of Carboniferous carbonate reservoirs applied to the eastern edge of the Pre-Caspian Basin was established. Four types of pore-throat structures were developed which were wide multimodal mode, wide bimodal mode, centralized unimodal mode and asymmetry bimodal mode, respectively. The discriminant index of pore-throat structure was proposed, realizing the quantitative characterization of pore-throat structure types. (2) The microscopic heterogeneity of pore reservoir was the strongest and four types of pore-throat structures were all developed. The pore-fracture and pore-cavity-fracture reservoirs took the second place, and the microscopic heterogeneity of pore-cavity reservoir was the weakest. It was revealed that the main controlling factor of pore-throat structure was the combination patterns of reservoir space types formed by sedimentation, diagenesis and tectonism. (3) It was revealed that the development of various pore-throat structure types was the important factor affecting poroperm relationship of reservoirs. The calculation accuracy of permeability of reservoirs can be improved remarkably by subdividing the pore-throat structure types. This study deepens the understanding of pore-throat structure of complicated carbonate reservoirs, and is conducive to classification and evaluation, establishment of precise porosity-permeability relationship and highly efficient development of carbonate reservoirs.

Deep oil

Regardless of the direction of development and changes in the energy sector, the Worlds economies will rely primarily on natural resources for at least the next 20 years and very likely beyond. Actually, the resources of hydrocarbons in place in comparison with consumption are almost inexhaustible, so the question is only in the cost of production. For this reason, the exploration for new commercial fields that can withstand price volatility over a long period of time will play a critical role. At the same time, one of the most promising areas is the exploration of the new super-deep (more than 6000 m.) oil and gas accumulations.
 The information presently accumulated by geologists allows a high probability of finding profitable reserves, including liquid hydrocarbons, in ultra-deep horizons that were previously considered non-perspective due to extremely adverse thermobaric conditions. Commercial oil and gas potential of various sedimentary formations in such conditions is established for more than 70 basins around the world. There are large and giant gas, gas condensate, oil and mixed phase-heterogeneous fields, of which more than 1,200 are already being developed. Over the past 10 years, the most significant success has been achieved in the Gulf of Mexico (USA, Mexico), the Tarim and Sichuan basins (China), the South Caspian basin (Azerbaijan, Russia and Kazakhstan), the Santos basin (Brazil), and the Arab basin (Middle East). More than 120 hydrocarbon fields were discovered and most of them have yet to prove their commerciality.
 Pre Caspian basin is one of the most prospective regions, where deep horizons are poorly explored. For a better understanding of its potential, statistics on 106 clastic and 36 carbonate fields was collected, and 22 Paleozoic basins were considered as analogs. Data from 15084 documents with varying degrees of significance was taken into consideration; and elements of Artificial Intelligence (AI) processing were applied. Their simultaneous interactive analysis allowed to identify several possible analogues for Pre-Caspian basin and to justify the exceptionally high perspectives of its ultra-deep horizons.
 Many analysts identify three strategic directions for EP activities. The first type includes new perspective horizons in new basins, the second direction is associated with new reservoirs in already known oil and gas basins, and the last, third type includes prospects in already known productive sections of previously explored basins. Pre Caspian basin to some extent, corresponds to all three groups, but mainly to the second and third. Main interest is associated with well-studied Devonian reservoirs on the periphery, rapidly dropping towards the center of the basin, or with almost unexplored to date lower Paleozoic horizons. This article opens a series of publications devoted to the topic of discovery and development of ultra-deep hydrocarbons.

Features of the Structure and Development of the Southeastern Part of the East European Platform and the Caspian Basin in the Late Precambrian‒Early Paleozoic

The geological and sedimentological interpretation of several time and deep seismic profiles within junction zone of the Volga‒Ural area of the East European Platform, Pre-Caspian Depression, Ural Foredeep, Bashkir Anticlinorium, and northern margin of the Scythian Platform allowed us to identify a number of previously unknown structural features of Later Precambrian and Early Paleozoic formation. On this basis, structural-facies maps were compiled for the Riphean and Vendian stages of development. It was shown that as a result of the collision of the southeastern passive margin of the continent Baltica with Scythia in the Early Vendian and with the Timanides of the Urals in the Later Vendian, a complex tectonic structure of the Orenburg tectonic node was formed, which forms the foundation of the Caspian oil and gas province. The results obtained substantially clarify the structure of the sedimentary cover of the East European Platform and the Pre-Caspian Basin, the stages of the formation and evolution of their structure, and the degree of influence on the sedimentation of structural changes in the adjacent territories of the folded Urals and the Scythian Platform.

Post-salt trapping mechanism of south-east Pre-Caspian and its application to petroleum exploration

The Kungurian saliferous sediments of the Pre-Caspian sedimentary basin represented by thick stratum of rock salt with interlayered lenses of anhydrites, terrigenous and carbonate rocks. Initial thickness of these sediments estimated as 4000–4500 m at the center of the depression and 1000–2000 m on the edges of the basin. The processes of halokinesis led to formation of more than 1200 salt dome structures represented by salt diapirs and walls, ridges and salt pillows. Number of salt dome related structures of Mesozoic clastic deposits revealed by seismic exploration carried out in 70–90′s of last century are quite common on the south-eastern part of the Pre-Caspian Sedimentary basin. Most of hydrocarbon pools in post-salt clastic rocks have been discovered on fault-related anticline prospects which are derived from salt tectonics morphologically variable (Munyithya et al. Petrol Explor Prod Technol 10: 2257–2267. https://doi.org/10.1007/s13202-020-00917-1, 2020). Other potential traps anticipated in the area are stratigraphic traps, pinch-out and unconformity-related traps, trapped by salt domes and walls or by salt overhang, etc.

Origin, distribution and implications on production of bedding-parallel fractures: A case study from the Carboniferous KT-Ⅰ Formation in the NT oilfield, Precaspian Basin, Kazakhstan

Bedding-parallel fractures (BPFs) are the breakage of rocks along weakness bedding plane of stratification or foliation. At present, the research of fractures is primarily focused on high-angle structural fractures (SFs), but few systematic efforts have been made on the formation mechanism, distribution and influences on oil production of BPFs. Knowledge of attributes of BPFs in carbonate reservoirs is necessary for well-site design and reservoir waterflooding development.Observation and description of cores and image logging and laboratory measurements including cathodoluminescence (CL), fluid inclusion, acoustic emission experiments, porosity, permeability and well testing data were used to gain insight into the formation mechanism, controlling factors and impacts on oil production of BPFs. The results show that the length and aperture of BPFs range from centimeters to tens of meters and from 30 μm to 100 μm respectively. BPFs are primarily shear fractures without cements in the study area. There are 3 periods of SFs in the study area and the formation timing of BPFs and the SFs of the 2nd period are simultaneous. The origin of BPFs is related to the development of thrust faults and folds. Shear BPFs were the result of interlayer sliding during the formation of anticline and thrusts under the effect of tectonic compaction. Extension BPFs formed because of the relative movement of the hanging wall and footwall of the thrust faults. Shear BPFs are more common than extension BPFs because both anticline and thrusts can result in the formation of shear BPFs. Many factors can govern the development of BPFs including structural position, rock composition and structure, distance to faults and bed thickness. The formation of BPFs is promoted by low structural position, rapid vertical changes of the rock composition, small grain size, close distances to faults and thin bed thickness. Although the aperture of low-angle BPFs is smaller than that of fractures at high angle to bedding due to the influence of overburden pressure, the low-angle BPFs can partially improve the reservoir permeability and partly enhance the initial production of individual wells.

Characteristics and principal controlling factors of sub-salt oil and gas accumulation in the eastern margin of the Precaspian Basin

Characteristics and principal controlling factors of sub-salt oil and gas accumulation in the eastern margin of the Precaspian Basin

Comprehensive geochemical study of core and cutting samples from postsalt deposits of southern parts of precaspian basin and «oil-source rocks» correlation studies

Comprehensive geochemical study of core and cutting samples from postsalt deposits of southern parts of precaspian basin and «oil-source rocks» correlation studies

Depositional environment, diagenetic evolution, and their impact on the reservoir quality of the carboniferous KT-Ⅱ carbonate in the zhanazhol reservoir, Pre-Caspian Basin, Kazakhstan

Abstract The Carboniferous KT-Ⅱ carbonate unit (Late Serpukhovain to Early Moscovian) of the Zhanazhol reservoir in the Pre-Caspian Basin is a giant condensate reservoir with great heterogeneity. Although the depositional characteristics and their impact on reservoir quality have been well documented by previous studies, few studies have focused on diagenesis, the interplay between depositional environment, and their controls on reservoir heterogeneity. In this study, combining sedimentological, petrographic and geochemical analyses, we reconstructed the depositional settings and diagenetic history of the KT-Ⅱ carbonate and assess their impacts on reservoir quality. According to the vertical and lateral distribution of 12 observed microfacies types, we proposed a depositional model of a northward-deepening ramp consisting of tidal flat, inner ramp, and middle ramp, which has played a critical role in controlling the reservoir quality mainly through grain types and matrix content. Fusulinidal grainstones/packstones have the best reservoir quality because of its porous fusulinidal fragments and low micritic matrix content. The major diagenetic events, including cementation (eight cement types), dissolution (fabric and non-fabric-selective dissolution), compaction, pressure dissolution and microfracturing (early and late), were grouped into six diagenetic environments: marine, meteoric, shallow burial, epigenic karstification, intermediate burial, and deep burial. Marine cementation and compaction are the main reason for porosity decreasing in upper inner ramp and middle ramp, respectively. The minor moldic pores created by fabric-selective dissolution during meteoric stage were enlarged by freshwater leaching during epigenic karstification, and its associated cementation occluded pores in the underlying bioclastic grainstones/packstones. Late non-fabric-selective dissolution and cementation likely resulted in local porosity rearrangements without net porosity gain or loss, but certainly reduced reservoir heterogeneity. The interaction between depositional environment and diagenetic evolution played a vital role in the formation of two types of vertical distribution patterns of porosity (types Ⅰ and Ⅱ). Understanding this interaction and its impacts on reservoir quality within a sequence-stratigraphic framework can more reliably predict the distribution of reservoir properties, and provides insights for adjacent fields with similar settings.

ТИПИЗАЦИЯ РАЗРЕЗОВ ПАЛЕОЗОЙСКОГО КОМПЛЕКСА ВОСТОЧНОГО БОРТА ПРИКАСПИЙСКОЙ ВПАДИНЫ

The present article highlights the features of the geological structure, sedimentation conditions and the influence tectonic evolution factors on the petroleum potential within the eastern edge of the Precaspian basin. According to the features of the geological structure and lithological characteristics of the sedimentary formations of the eastern edge of the Precaspian basin, different facies zones can be distinguished, corresponding to the distinguished structural-formational zones with several types of Paleozoic sections. НЕФТЬ И ГАЗ 2021 1 (121) 7 ГЕОЛОГИЯ Based on the comparison of the Paleozoic sections for the eastern edge of the Precaspian basin it is concluded that collision tectonics was the major factor for sedimentation. Vertical facies succession influenced by tectonics and sea level fluctuations. Carbonate platforms played an important role in the distribution of sedimentary material and controlled the depth of the sea, which influenced on the composition and texture of the rocks. The presence of carbonate platforms was also reflected in the reduced thickness of the Lower Permian sediments, which are less presented within the carbonate platforms stratigraphic section comparing to the adjacent relatively deep-water areas located to the west outside the carbonate platforms. The structure of carbonate platforms was to the largest extent defined by the thrust tectonics and that controlled the distribution of oil and gas fields and potential traps.

A review of enhanced oil recovery (EOR) methods applied in Kazakhstan

Abstract 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.

Sedimentary characteristics and exploration direction in the south of the central block in Pre-Caspian Basin

The Pre-Caspian Basin experienced the history from the Late Paleozoic craton margin to the Mesozoic-Cenozoic depression. It has been explored for a long time. It is the most important oil and gas producing area in Kazakhstan, and a large number of oil and gas fields have been discovered in it. The oil and gas discoveries are located in clastic rock and platform carbonate rock below the Lower Permian salt domes. The study area is located at the eastern margin of the Pre-Caspian Basin, where reservoirs are deposited in an open carbonate platform in the shallow sea. The most developed subfacies are intraplatform shoals and sea between shoals. The microfacies in the intraplatform shoals include bioclastic shoals and algae shoals, and represent dominant high-quality reservoirs. The central gentle zone and the eastern slope zone in the study area are potential targets for exploration and evaluation. All reservoirs are structural-lithologic reservoirs controlled by high lithologic barriers or updipped pinch-outs.