Sandy Conglomerate Research Articles

Adsorption Behavior of Different Components of a Polymer/Surfactant Composite Control System along an Injection-Production Channel in Sand Conglomerate Reservoirs.

Sandy conglomerate reservoirs have become an important replacement area for unconventional energy to increase reserves and production. The polymer/surfactant composite control flooding system can effectively alleviate the water flooding front breakthrough caused by the interlayer or plane heterogeneity of the sand conglomerate reservoir and is an effective production method to reduce the water cutoff of the well and increase the oil recovery. In the process of controlling the oil displacement process of the system, the chromatographic separation effect was found due to the different viscosities of each component and the adsorption difference between the components and the rock, which weakened the development effect of the reservoir. It is necessary to study the adsorption law of each component of the complex controlled displacement system along the injection-production channel in the sand conglomerate reservoir. In this study, the microstructure and mineral composition of sandy conglomerates were determined by scanning electron microscopy and X-ray diffraction tests. The main particle size distribution was counted through a rock particle sieving experiment. A new characterization method called the large-size core physical model was used. The composite control system of sulfonate and betaine was used as the surfactant component, and the adsorption degree of each component in the displacement process was analyzed. The experimental results showed that the mass fraction of the sandy conglomerate increased with the decrease in particle size. The particles with a size of less than 0.08 mm account for a relatively high proportion, with a mass fraction of 60%. The content of brittle minerals, such as quartz and feldspar, in the glutenite was relatively high, and micrometer-sized pores and fractures were developed. The main factors affecting the viscosity of the composite system were the concentration and molecular weight of the polymer. The increase of injection volume of the flooding system is conducive to the maintenance of ultralow interfacial tension migration to the deep core. In the displacement process, when the polymer molecular chain was cut to a certain extent, the effect of throat shear was also slowed due to the short molecular chain. However, the shortened polymer molecules were more easily adsorbed on the surface of rock particles and the adsorption rate increased. The adsorption capacity of each component gradually decreased with the increase of the injection volume and injection concentration. The relative content of the composite control system and crude oil affects the type of emulsion, which undergoes a corresponding transformation during the driving process from a water-in-oil emulsion to an oil-in-water one. The research results of this paper enrich the mechanism of enhancing oil recovery of sand conglomerate reservoirs by polymer-surfactant composite regulation technology.

Application of Geological Engineering Integration in Tight Sandy Conglomerate Horizontal Well

Application of Geological Engineering Integration in Tight Sandy Conglomerate Horizontal Well

Variability of sequence architecture in a rift margin controlled by tectonic activity: The Eocene Dongying Depression, Bohai Bay Basin, China

AbstractSequence architectures along the margins of rift basins are still poorly documented compared to passive continental margin settings. The Eocene Shahejie Formation on the rift margin of the Dongying Depression records a complex sequence stratigraphic distribution of conglomerate, sandy conglomerate, sandstone and mudstone. These facies have been mainly attributed to fan delta and marginal subaqueous fan depositional settings that developed during segmented fault activity along the rift margin. We utilize three‐dimensional (3D) seismic data, conventional cores, and wireline log data to dissect the overall wedge‐shaped upper sub‐member strata of the Shahejie Formation's fourth member. The study interval is a third‐order sequence formed between 45.4 and 42.5 Ma and contains a lowstand–transgressive systems tract (LST–TST) and a highstand systems tract–falling‐stage systems tract (HST–FSST). We found that the LST–TST developed several huge amalgamated depocenters along the Chennan border fault; whereas, these depocenters gradually diminished or even disappeared during the HST–FSST period, illustrating less significant control by the border fault. Through calculations of strata growth rates, we confirmed that the segmented activity of the border fault influences the stratigraphic distribution and facies evolution during these two periods. Specifically, deep‐water depositional systems, represented by marginal subaqueous fans were widely developed in the LST–TST period and were influenced by overall strong tectonic activity, including retrogradational (R) and aggradational (A) patterns. However, the aggradational to progradational (AP) deltas and progradational to degradational (PD) deltas dominated the generally muted tectonic activity setting during the HST–FSST. Additionally, influenced by localized segmented fault activity, these systems tracts exhibit incomplete vertical development, resulting in spatial variability in stratigraphic stacking patterns.

Genetic mechanisms of high-quality tight siliciclastic reservoirs: A case study from the Upper Triassic Xujiahe Formation in the Yuanba area, Sichuan Basin, China

This study analyzed the petrological characteristics, diagenesis, pore types, and physical properties of the tight coarse-grained siliciclastic sequences in the third member of the Upper Triassic Xujiahe Formation (also referred to as the Xu-3 Member) in the western Yuanba area in the northeastern Sichuan Basin, China, based on the results of 242.61-m-long core description, 292 thin-section observations, scanning electron microscopy (SEM), and 292 physical property tests. The types and genetic mechanisms of high-quality tight coarse-grained siliciclastic reservoirs in this member was determined thereafter. The research objective is to guide the exploration and development of the tight coarse-grained siliciclastic sequences in the Xu-3 Member. The results of this study are as follows. Two types of high-quality reservoirs are developed in the coarse-grained siliciclastic sequences of the Xu-3 Member, namely the fractured fine-grained sandy conglomerate type and porous medium-grained calcarenaceous sandstone type. Hydrodynamic energy in the sedimentary environment is the key factor controlling the formation of high-quality reservoirs. These high-quality reservoirs are developed mainly in the transitional zone with moderately high hydrodynamic energy between delta-plain braided channels and delta-front subaqueous distributary channels. The dolomitic debris (gravel) content is the main factor affecting the reservoirs’ physical properties. The micritic algal debris and sandy debris in the dolomitic debris (or gravels) tend to recrystallize during burial, forming intercrystalline pores within. In the medium-grained calcarenaceous sandstones, intercrystalline pores in the dolomitic debris are formed at the early diagenetic stage, and a pore system consisting of structural fractures connecting intergranular pores, intergranular dissolution pores, and kaolinite intergranular micropores is developed at the late stage of diagenesis. The formation of intercrystalline pores in dolomite gravels and gravel-edge fractures, a pore system connected by gravel-edge and tectonic fractures, is closely related to the dolomite gravels in the sandy fine-grained conglomerates.

Micromechanism and mathematical model of stress sensitivity in tight reservoirs of binary granular medium

Research on reservoir rock stress sensitivity has traditionally focused on unary granular structures, neglecting the binary nature of real reservoirs, especially tight reservoirs. Understanding the stress-sensitive behavior and mathematical characterization of binary granular media remains a challenging task. In this study, we conducted online-NMR experiments to investigate the permeability and porosity evolution as well as stress-sensitive control mechanisms in tight sandy conglomerate samples. The results revealed stress sensitivity coefficients between 0.042 and 0.098 and permeability damage rates ranging from 65.6% to 90.9%, with an average pore compression coefficient of 0.0168–0.0208 MPa−1. Pore-scale compression occurred in three stages: filling, compression, and compaction, with matrix pores playing a dominant role in pore compression. The stress sensitivity of binary granular media was found to be influenced by the support structure and particle properties. High stress sensitivity was associated with small fine particle size, high fines content, high uniformity coefficient of particle size, high plastic deformation, and low Young's modulus. Matrix-supported samples exhibited a high irreversible permeability damage rate (average = 74.2%) and stress sensitivity coefficients (average = 0.089), with pore spaces more slit-like. In contrast, grain-supported samples showed low stress sensitivity coefficients (average = 0.021) at high stress stages. Based on the experiments, we developed a mathematical model for stress sensitivity in binary granular media, considering binary granular properties and nested interactions using Hertz contact deformation and Poiseuille theory. By describing the change in activity content of fines under stress, we characterized the non-stationary state of compressive deformation in the binary granular structure and classified the reservoir into three categories. The model was applied for production prediction using actual data from the Mahu reservoir in China, showing that the energy retention rates of support-dominated, fill-dominated, and matrix-controlled reservoirs should be higher than 70.1%, 88%, and 90.2%, respectively.

New insight into imbibition micromechanisms and scaling model in fossil hydrogen energy development of tight reservoirs based on NMR

Spontaneous imbibition is an important mechanism for developing fossil hydrogen energy. However, the research of imbibition micromechanisms and scaling methods in tight reservoirs with complex lithofacies remains limited. This study employed Nuclear magnetic resonance (NMR) monitoring to investigate imbibition at multiscale pores in tight sandy conglomerate samples. Then, a modified shut-in time-scale model was developed analyzing the imbibition modes and control factors. The results showed that the imbibition concludes three stages: suction, diffusion, and stable. The diffusion stage is crucial for promoting recovery. Two modes of imbibition in four lithofacies were distinguished: stable type (recovery>40 %) and sensitive type (recovery<20 %). Samples with medium permeability (0.2mD-0.6mD), bimodal pore distribution, and less illite/smectite mixed-layer (relative content<50 %) had high recovery. Nanopores provided foremost oil supply, while macropores facilitated fluid interchange. “Relay imbibition” from micropores to macropores was an important recovery mechanism. Hydrogen signals during clay expansion and microcracks propagation were identifiable by NMR-T2 after accounting for ferromagnets and temperature. The imbibition diffusion radius derived from T2 accumulation was found to modify the normalized time-scale model for complex lithofacies tight reservoirs. Consequently, the reasonable shut-in time for stable and sensitive reservoirs was concluded to be 32 and 11 days, respectively.

Sedimentary Characteristics and Hydrocarbon-Generation Potential of the Permian Pingdiquan Formation in Dongdaohaizi Sag, Junggar Basin, Northwest China.

After several years of extensive exploration, a series of oil and gas reservoirs or structures have been discovered in the Dongdaohaizi sag, situated in the hinterland of the Junggar Basin. However, in recent years, some wells around the sag have failed. Herein, sedimentary facies, the plane distribution of dark mudstone, geochemical characteristics of source rocks, and the control of sedimentary facies on the distribution and development of source rocks in the Permian Pingdiquan Formation in the Dongdaohaizi sag were systematically investigated. A combined geological and geochemical method was used to fully understand the distribution law and resource potential of the source rocks in this area. Investigation results indicate that the Pingdiquan Formation primarily inherited continuous deposition, and the sedimentary facies of the sag, such as semideep lake, shore-shallow lake, prefan delta, fan delta front, and fan delta plain, were developed from the center sag to the outside. The fan delta facies, predominantly distributed in the northern margin of the sag, are characterized by lithology mainly composed of sandy conglomerate and coarse sandstone. The sandstone has a coarse particle size and poor sorting ability, while lacustrine mudstone is widely developed in the sag with a large sedimentary thickness, which is the primary source rock of the Dongdaohaizi sag. The source rocks in the Pingdiquan Formation exhibit medium-to-good quality. The organic matter is categorized as types II1-III, and the thermal evolution maturity is in the mature-high mature stage, indicating a high resource potential. The development of the source rock in the Dongdaohaizi sag is closely related to the sedimentary environment. The sedimentation rate of fan delta facies is high and burial is fast, bringing a large amount of terrestrial organic matter to the lake, thereby increasing the nutrition and organic matter quantity of the lake. Due to the stable water of the lake, low energy at the bottom, and medium conditions of strong reduction, a large amount of organic matter accumulated in the deep to semideep lake facies of the study area, resulting in the development of thick dark mudstone with a thickness of over 400 m. The abundance of organic matter has reached a good level, and the maturity and content of organic matter are high, signifying a high hydrocarbon-generation potential.

Diagenetic differentiation of tuffaceous interstitial materials in sandy conglomerate and their effect on reservoir properties

Tuffaceous material of the Lower Triassic Baikouquan Fm., NE Junggar Basin is closely associated with detrital particles and particularly with crenulated quartz grains and kaolinite. The amount tuff is reduced closed to the source area. The main component of the tuffaceous interstitial material is SiO2, followed by K2O, FeO, and MgO. The tuffaceous interstitial material can be further divided into three types: medium (basic) potassium-rich tuffaceous material, ultrabasic iron-magnesium tuffaceous material, and ultrabasic iron-magnesium rich tuffaceous material. Medium (basic) potassium-rich is dominated by fusiform shrinkage pores, often associated with kaolinite, while ultrabasic iron-magnesium rich tuff pores are not developed, and ultrabasic iron-magnesium tuffaceous material is dominated by dissolution pores. The solution pores have large diameters and large volume of pores and throats, but low pores and throats coordination number. The pore size and the pores and throats volume of shrinkage fractures are small, but the pores and throats coordination number are large. Dissolution pores are mainly distributed in Mbr 1, whereas shrinkage pores mainly occur in Mbr 2. However, the interlayer productivity data from a single well show that the Mbr 1 has a higher productivity than Mbr 2. However, the interlayer productivity data from a single well show that Mbr 1 has a higher productivity than Mbr 2. In addition, tuff is not responsible for wind action, but the cause of intermittent water flow transport in volcanic rocks. Distributary channels at the fan delta front comprise the dominant facies for development of tuffaceous interstitial materials. The composition of tuffaceous interstitial material clearly determines reservoir quality. Medium basic potassium-rich tuff has a high SiO2 content and is prone to devitrification, so it is dominated by shrinkage pores, whereas ultrabasic iron-magnesium tuff contains FeO and MgO and is vulnerable to acid corrosion and the formation of corrosion pores. However, acid minerals such as kaolinite reduce reservoir connectivity. Compared with solution pores, shrinkage pores have a small pore volume, but high pores and throats coordination number, indicating that they have a high seepage capacity. Shrinkage pores are an important factor in causing production differences between single layers and should be given more attentions.

Multi-Scale and Multi-Region Pore Structure Analysis on Sandy Conglomerate Whole Core With Digital Rock Model

Abstract Based on industrial computed tomography (CT), the whole core sandy conglomerate is scanned with a resolution of 0.5 mm/voxel, and the representative debris region and filling region subsample is selected to be scanned with a resolution of 15 µm/voxel using micro-CT. Then, four regions of the whole core sandy conglomerate image are segmented with the multi-threshold segmentation algorithm including macro pore, debris, filling, and gravel regions, while binary segmentation is performed on the debris and filling subsamples to segment the debris pores and filling pores respectively. Finally, the multi-scale and multi-region pore network model of the sandy conglomerate was constructed by the integration method to analyze the different types of pore characteristics. It can be found that the integrated sandy conglomerate model can reflect the structural characteristics of macro pore, debris pore, and filling pore at the same time. Meanwhile, the porosity and permeability of the integrated sandy conglomerate model are calculated and they are basically consistent with that of lab test results, which greatly increase the accuracy of the multi-scale multi-region pore network model.

Muddy and sandy conglomerates: Mixing between gravelly slurry flow and substrates in a fan-delta system, Junggar Basin, Northwest China

Mixing of a gravity flow with substrate over which it travels can control flow transformations with implications for the structure of the deposit that is left; however, the effects of mixing in conglomerate-dominated gravelly underflow in lacustrine environments remain poorly understood. This study documents two types of interactions between gravelly underflow and substrate and the resulting conglomerate deposits across a lacustrine fan-delta system in the Junggar Basin, northwest China. The resulting conglomerates are typically massive, poorly sorted, clast-supported without reserve grading; rich in mudstone clasts; and having been emplaced by river-derived hyperpycnal flow. Based on the character of the matrices between the clasts, conglomerates are divided into three sub-categories: (i) muddy (mud-rich) conglomerates with a mainly fine-grained muddy matrix, (ii) sandy (mud-poor) conglomerates with a mainly sandy matrix, and (iii) mud-bearing sandy conglomerates with a coexisting mud-sand matrix. Furthermore, two distinct lithological associations were identified: (i) a regularly recurring tripartite conglomerate unit interlayered with mudstone (S I) and (ii) a regularly recurring tripartite conglomerate unit interlayered with sandstone (S II). Both lithological associations contained a recurring tripartite conglomerate unit with a basic tripartite structure consisting of muddy conglomerates in the lower division, mud-bearing sandy conglomerates in the middle division, and sandy conglomerates in the upper division. There was more sand in the upper layers of the tripartite conglomerate unit matrix. Muddy conglomerates with large amount of mudstone clasts are thought to form through extensive erosion and mixing between the lower part of the flow with mud-substrate on the lake bottom, whereas central mud-bearing conglomerates and upper sandy conglomerates are considered to be generated by successively weaker mixing in the upper part of the flow. The consequent sandy trailing flow resting upon the previously-emplaced tripartite conglomerate unit forms a thinner sandstone bed that acts as a “sand mat” for the next incoming gravelly flow. A single sandy conglomerate bed subsequently forms above when gravel mixes with the sand substrate, as opposed to forming muddy conglomerates that were generated by mud from eroded substrate. Our results show that the erosion and mixing of sediment flow with substrate are important factors in flow transformation and deposition and that the substrate type (muddy or sandy) along the flow path plays a crucial role in controlling flow behavior and reservoir characteristics.

Stress Interferences between Fractures and Fracturing Stages of a Horizontal Well in a Sandy Conglomerate Reservoir in Junggar Basin, Northwest China

The sandy conglomerate reservoirs in the Mahu oilfield located in the Junggar Basin of Northwest China are featured by a significant horizontal stress difference between two directions, making formations easy to form double-wing fractures upon hydraulic fracturing instead of creating a complex fracture network. In addition, as the well spacing or interval cluster spacing decreases, the stress interferences between hydraulic fractures strengthen accordingly, leading to more difficulties in the prediction of fracture propagation patterns. Given the geological characteristics in the study area, an extended finite element method (XFEM) based hydraulic fracture model that can handle fracturing fluid flow distribution was proposed to evaluate the seepage, stress, and damage of the formation under hydraulic fracturing. The influences of the initial stress difference, cluster spacing, and fracturing stage sequence on the hydraulic fracture stress interference and the fracture propagation were investigated, producing discoveries that include: (1) as the fractures propagate, the stress difference between two fractures changes as well, and such change is also affected by the initial stress difference and the fracture distance; (2) the postfracturing stress difference first decreases but then increases with the increase in cluster spacing; (3) as the cluster spacing increases, the interfracture stress interference decreases. In addition, the outer fractures suppress the length of the middle fractures, thus limiting the stimulated reservoir area (SRA); (4) for the cases of creating multistage fractures, the later fracturing stage experiences both the interfracture and the interstage stress interferences from the prefracturing stage. As the fracture width changes with time, the nonplanar fracture feature of the later fracturing stage becomes more evident while the corresponding SRA decreases.

Heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in foreland thrust belts: A case study of deep Cretaceous Qingshuihe Formation clastic reservoirs in southern Junggar Basin, NW China

Using the data of drilling, logging, core, experiments and production, the heterogeneity and differential hydrocarbon accumulation model of deep reservoirs in Cretaceous Qingshuihe Formation (K1q) in the western section of the foreland thrust belt in southern Junggar Basin are investigated. The target reservoirs are characterized by superimposition of conglomerates, sandy conglomerates and sandstones, with high content of plastic clasts. The reservoir space is mainly composed of intergranular pores. The reservoirs are overall tight, and the sandy conglomerate has the best physical properties. The coupling of short deep burial period with low paleotemperature gradient and formation overpressure led to the relatively weak diagenetic strength of the reservoirs. Specifically, the sandy conglomerates show relatively low carbonate cementation, low compaction rate and high dissolution porosity. The special stress-strain mechanism of the anticline makes the reservoirs at the top of the anticline turning point more reformed by fractures than those at the limbs, and the formation overpressure makes the fractures in open state. Moreover, the sandy conglomerates have the highest oil saturation. Typical anticline reservoirs are developed in deep part of the thrust belt, but characterized by “big trap with small reservoir”. Significantly, the sandy conglomerates at the top of anticline turning point have better quality, lower in-situ stress and higher structural position than those at the limbs, with the internal hydrocarbons most enriched, making them high-yield oil/gas layers. The exponential decline of fractures makes hydrocarbon accumulation difficult in the reservoirs at the limbs. Nonetheless, plane hydrocarbon distribution is more extensive at the gentle limb than the steep limb.

Heterogeneity of a Sandy Conglomerate Reservoir in Qie12 Block, Qaidam Basin, Northwest China and Its Influence on Remaining Oil Distribution

In view of the key geological factors restricting reservoir development, the reservoir heterogeneity of an alluvial fan sandy conglomerate reservoir in the Qie12 block of Qaidam Basin, Northwest China, and its influence on remaining oil distribution, were studied according to geology, wireline logging data, and dynamic production data. This study illustrates that the difference in pore structures, which are controlled by different sedimentary fabrics, is the main cause of reservoir microscopic heterogeneity. Besides, the temporal and spatial distribution of architectural units in the alluvial fan controls reservoir macroheterogeneity. Our results show that the thick sandy conglomerate develops two types of pores, two types of permeability rhythms, two types of interlayers, two types of interlayer distribution, two types of effective sand body architecture, and four types of sand body connecting schemes. The strongest plane heterogeneity is found in the composite channel unit formed by overlapping and separated stable channels of the middle fan, and the unit’s permeability variation coefficient is &gt;0.7. However, the variation coefficient in the range of 0.3–0.5 is found in the extensively connected body unit sandwiched with intermittent channels of the inner fan. The distributions of the remaining oil vary significantly in different architectural units because of the influence of reservoir heterogeneity, including distribution patterns of flow barriers, permeability rhythm, and reservoir pore structures. The composite channel unit formed by overlapping and separated stable channels, or the lateral alternated unit with braided channel and sheet flow sediment of the middle fan, is influenced by the inhomogeneous breakthrough of injection water flowing along the dominant channel in a high-permeability layer. The microscopic surrounding flow and island-shaped remaining oils form and concentrate mainly in the upper part of a compound rhythmic layer. Meanwhile, in the extensively connected body unit sandwiched with intermittent channels of the inner fan, poor injector–producer connectivity and low reservoir permeability lead to a flake-like enrichment of the remaining oil.

Diagenesis, Diagenetic Facies and Their Relationship with Reservoir Sweet Spot in Low-Permeability and Tight Sandstone: Jiaxing Area of the Xihu Sag, East China Sea Basin

The optimization of reservoir sweet spots is the key to the efficient exploration and development of low-permeability and tight sandstone gas reservoirs. However, offshore deep, low-permeability and tight sandstone has the characteristics of large burial depth, large diagenesis heterogeneity and prominent importance of diagenetic facies, which make it difficult to predict reservoir sweet spots. This work comprehensively used logging data, core observation, conventional core analysis, thin section, powder particle size analysis, clay X-ray diffraction analysis, cathode luminescence analysis, scanning electron microscopy and energy spectrum analysis and carried out the study of diagenesis, diagenetic facies and reservoir sweet spots of low-permeability and tight sandstone of H3 and H4 (the third and fourth members of Huagang Formation) members in the Jiaxing area of the Xihu Sag. The results show that the H3 and H4 sandstones were divided into five diagenetic facies types, and chlorite-coated facies and dissolution facies were favorable diagenetic facies belts. The H3 member mainly develops chlorite-coated facies, dissolution facies and quartz-cemented facies, whereas the H4 member primarily develops quartz-cemented facies and chlorite-coated facies. The percentages of type I sweet spot, type II1 sweet spot and type II2 sweet spot in the H3 reservoir are approximately 21%, 23% and 26%, respectively, whereas the percentages of type I sweet spot, type II1 sweet spot and type II2 sweet spot in the H4 reservoir are about 16%, 15% and 16%, respectively. The distribution rules of reservoir sweet spots were investigated. Type I sweet spot was mainly developed in the areas of chlorite-coated facies and dissolution facies of medium sandstone and coarse sandstone in the channel bar and braided channel sedimentary microfacies. Type II sweet spot was primarily distributed in the areas of quartz-cemented facies, chlorite-coated facies and minor dissolution facies of medium sandstone, fine sandstone and sandy conglomerate in the braided channel, subaqueous distributary channel and channel bar sedimentary microfacies. Type III sweet spot was chiefly developed in the areas of tightly compacted facies, calcite-cemented facies and quartz-cemented facies of fine sandstone, siltstone and a small amount of sandy conglomerate in the subaqueous distributary channel sedimentary microfacies.

Study the Elastic Parameters of Sandy Conglomerate under Different Burial History and Petrophysical Modeling

Over the past few years, significant exploration breakthroughs have been made in the sandy conglomerates reservoir of the Triassic Baikouquan Formation in the Mahu Sag, Junggar Basin, China. However, the elasticity and pore characteristics of the tight sandy conglomerates reservoir in this area are still unclear. Through a systematic sonic testing program of the sandy conglomerates sample collected from the Mahu Sag, the regularity behind the variation of the elasticity and pore characteristics of the sample has been analyzed and captured. The Triassic Baikouquan Formation of the slope of Mahu Sag has been through complex burial and diagenetic history. The compaction, cementation, and dissolution are the three types of diagenesis that have the greatest impact on pore characteristics in the study area. In order to quantitatively describe the influence of this complex burial and diagenetic history, we present a rock-physics modeling approach to describe the elastic properties of sandy conglomerate sample. The overall strategy of the modeling is to combine the contact cement theory (CCT), differential effective medium (DEM) and the upper Hashin-Shtrikman bound. The CCT model can well describe the history of cementation, DEM model is suitable for the history of dissolution, and HS upper bound is used to describe the history of compaction. Then, the model is used to describe well log data from sandy conglomerates reservoirs in Mahu Sag and successfully explain the rock porosity, pore shape trends, and the elasticity in the sandy conglomerate reservoirs.

Elaborated Porosity and High-Quality Reservoirs in Deeply Buried Coarse-Grained Sediment: Insight of the Sublacustrine Sandy Conglomerates in the Eocene Shehejie Formation (Es4), Dongying Subbasin, Bohai Bay Basin, China

Reservoir porosity evaluation is crucial for successful prediction of reservoir quality in deeply buried heterogeneous strata. Recent studies have demonstrated that high-quality reservoirs occur in deeply buried strata. However, little is known about the details of pores related to the good reservoirs. The northern Dongying steep slope sandy conglomerate was investigated to understand the porosity related to high-quality reservoir formation in sandy conglomerate using seismic data, well-logs, SEM-EDS, cathodoluminescence, and optical microscopy. The result reveals three genetic pores: primary, secondary, and mixed pores. The dissolution porosity consists of intergranular pores, intragranular pores, intercrystalline pores, and moldic pores. The intergranular dissolution and enlarged pores are the main contributors to good reservoir quality among the different pores. The index of compaction indicates that compaction is the crucial factor diminishing the reservoir quality in the progradation sequences, while cementation stands as the critical factor for porosity reduction in the retrogradation sequences. Comparing the reservoir properties reveals that the dissolution porosity is more significant in the Es4s than the Es4x, which renders the Es4s reservoir relatively good compared to the Es4x. This study demonstrated that for oil exploration in the fourth member of the Shahejie Formation, the Es4s should be prioritized.

Study on the standard of the four relationships of reservoir and the lower limit of effective reservoir in Nantun Formation of Oilfield A

By using the data of logging, cuttings logging, thin section identification and analysis in the study area to study the four characteristics of the Nantun Formation reservoir and their relationship, the lower limit standard of effective reservoir physical property is established by the logging interpretation model of the reservoir mud content, porosity, permeability and saturation, and the mercury injection method, oil production method, oil test analysis method and cumulative frequency statistics method. The lower limit standard of effective reservoir electrical property is determined by using fluid identification chart. The results show that the lithology of the second member of Nantun Formation is mainly sandy conglomerate, and the first member of Nantun Formation is mainly sandstone, and the sandstone is more developed. The oil content is mainly full of oil, oil spots and oil stains. The reservoir porosity is between 4~20% and permeability is 0.01~100 mD, showing low porosity and low permeability. The lower limit of effective reservoir in Nantun Formation is porosity of 7%, permeability of 0.05mD, sonic time difference of 63μs/ft, density of 2.55 g/cm3 and water saturation of 20%.

Impact of sedimentation and diagenesis on deeply buried sandy conglomerate reservoirs quality in nearshore sublacustrine fan: A case study of lower Member of the Eocene Shahejie Formation in Dongying Sag, Bohai Bay Basin (East China)

The sandy conglomerates of the lower member of Shahejie (Es4x) in the north of Dongying Sag, Bohai Bay Basin, were investigated to understand the formation mechanism of the good reservoir and controlling factors in deeply buried strata. This research is based on seismic, logging, and core data and comprehensively utilizes methods such as core description, petrographic analysis, cathodoluminescence image analysis, SEM-EDS analysis, and mercury intrusion. The sandy conglomerates are predominantly lithic arkose and litharenite. The reservoirs in the Es4x have experienced three diagenetic processes, compaction, dissolution, and cementation. Compaction remains the major factor affecting the reservoir quality, mainly in the progradation sequence, and cementation has a destructive effect on reservoirs, principally in the retrogradation sequence. The quantification of the compaction by the compaction index revealed that mechanical compaction is higher in the progradation sequence (0.68) than in the retrogradation sequences (0.59). Compaction is suppressed by carbonate cementation, but the extensive cementation significantly degrades the reservoir quality, especially in the retrogradation sequence. Dissolution of different rock fragments, feldspar, and the whole dissolution, in general, enhance the reservoir's quality in both intervals but more in the progradation sequence. Three types of reservoirs representing type I, type II, and Type III mercury intrusion capillary pressure curves were encountered in the Es4x. The braided channels in the progradation and retrogradation sets encompass the greatest reservoir quality and are characterized by type I and II reservoirs with good petrophysical properties. The preeminent reservoirs appear in the braided channels of the progradation set. The development of high-quality reservoirs is governed by the depositional subfacies, compaction, and dissolution in the Es4x. This study will contribute to comprehending the origin of the genesis mechanism of high-quality in deep sublacustrine sandy conglomerate and will help the exploration and pre-drill for favorable reservoirs in similar basins around the world.

Characteristics and prediction of permian tight glutenite reservoirs in dinan 15 well block, junggar basin

Glutenite reservoirs are characterized by rapid lateral change, strong heterogeneity, and complex main controlling factors. This research aims to identify macro and micro characteristics of glutenite reservoirs and establish criteria for identifying favorable reservoirs studies. To this end, the tight sandy conglomerate of the Upper Wuerhe Formation in the Permian Upper Wuerhe Formation in the Dinan 15 well area of the eastern slope of the Dongdaohaizi sag in the Junggar Basin is studied. The core observation, physical property analysis, sensitivity analysis, casting thin section, scanning electron microscope and logging data are adopted to comprehensively analyze the characteristics of glutenite reservoirs. By integrating various reservoir characteristic parameters, this work constructed a new set of reservoir evaluation criteria to predict favorable areas for the Upper Wuerhe Formation in Dongdaohaizi Sag. The results show that the lithology of the Upper Wuerhe Formation in the Dinan 15 well area is dominated by gray glutenite; the reservoir is an ultra-low porosity and ultra-low permeability reservoir with moderately weak water sensitivity and weak velocity sensitivity. The reservoir space types of the layers are mainly intergranular pores; the shape of the mercury intrusion curve and the pore throat radius distribution of the samples show that the reservoir is skewed, poorly sorted, and has the characteristics of small pores and thin throats. This work constructed evaluation criteria for reservoirs from I to III by utilizing lithology, physical properties, sensitivity, reservoir space type, and microstructural characteristics as key parameters. The favorable reservoir distribution area is mainly located in the west of the block, which is the focus of the next exploration of the Upper Wuerhe Formation area. The research results improved understanding of glutenite reservoir characteristics and will serve as significant guidance for the oil and gas exploration in the Dinan 15 well area.

Genesis and Accumulation Period of CO2 Gas Reservoir in Hailar Basin

Gas reservoirs with high CO2 have been found in several wells in the Hailar Basin. In this paper, a composition analysis, stable carbon isotope analysis, and a rare gas helium isotope 3He/4He and argon isotope 40Ar/36Ar analysis were carried out. These comprehensive analyses show that the CO2 in the Hailar Basin is inorganic-origin gas, which generally has the characteristics of crust–mantle-mixed CO2, and the fraction of helium of mantle source can reach 15.12~18.76%. There are various types of CO2 gas reservoirs. CO2 gas mainly comes from deep crust. The distribution of gas reservoirs is mainly controlled by deep faults and volcanic rocks, as well as by reservoir properties and preservation conditions. Magmatic rocks provide gas source conditions for the formation of inorganic CO2 reservoirs. Deep–large faults provide the main migration channels for CO2 gas. The sandy conglomerate and bedrock weathering crust of the Nantun Formation and the Tongbomiao Formation provide favorable reservoir spaces for the formation of CO2 gas reservoirs. The combination of volcanic rock mass and deep–large faults creates a favorable area for CO2 gas accumulation. The age of magmatic intrusion and the homogenization temperature of oil–gas inclusions in Dawsonite-bearing sandstone indicate that 120 Ma in the Early Cretaceous was the initial gas generation period of the CO2 reservoir and that oil and gas were injected into the reservoir in large quantities in 122~88 Ma. This period is the peak period of magmatic activity in Northeast China, as well as when the crust of Northeast China greatly changed. A large-scale CO2 injection period occurred in 100~80 Ma, slightly later than the large-scale injection period of the oil and gas. Since the Cenozoic, the structure has been reversed, and the gas reservoir has been adjusted.