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Core, thin section, conventional and image logs are used to provide insights into distribution of fractures in fine grained sedimentary rocks of Permian Lucaogou Formation in Jimusar Sag. Bedding parallel fractures are common in fine grained sedimentary rocks which are characterized by layered structures. Core and thin section analysis reveal that fractures in Lucaogou Formation include tectonic inclined fracture, bedding parallel fracture, and abnormal high pressure fracture. Bedding parallel fractures are abundant, but only minor amounts of them remain open, and most of them are partly to fully sealed by carbonate minerals (calcite) and bitumen. Bedding parallel fractures result in a rapid decrease in resistivity, and they are recognized on image logs to extend along bedding planes and have discontinuous surfaces due to partly-fully filled resistive carbonate minerals as well as late stage dissolution. A comprehensive interpretation of distribution of bedding parallel fractures is performed with green line, red line, yellow line and blue line representing bedding planes, induced fractures, resistive fractures, and open (bedding and inclined) fractures, respectively. The strike of bedding parallel fractures is coinciding with bedding planes. Bedding parallel fractures are closely associated with the amounts of bedding planes, and high density of bedding planes favor the formation of bedding parallel fractures. Alternating dark and bright layers have the most abundant bedding parallel fractures on the image logs, and the bedding parallel fractures are always associated with low resistivity zones. The results above may help optimize sweet spots in fine grained sedimentary rocks, and improve future fracturing design and optimize well spacing.

Multi-elemental analysis of particulate matters is highly desirable for the identification of their emission sources. However, the traditional techniques for single particle analysis usually require time-consuming sample preparation procedures. We report here a system that combines bright-field microscopy with laser induced breakdown spectroscopy (LIBS), allowing rapid and multi-elemental analysis of single particles. The improved throughput of the system was benefited from the use of ultra-thin polyethylene films for particle immobilization such that their spectra were collected successively. The simple composition of the films avoided their interferences in the particles’ LIBS spectra. Moreover, the small thickness of the films allowed their rapid vaporization during laser ablation such that the plasma emissions from the particles were not quenched by their substrates. The performances of the system were demonstrated by studying the heterogeneity in particles’ compositions and discriminating dust particles with very similar chemicals, suggesting that it is a promising tool for environmental risk assessment.

Low oil saturation reservoirs are increasingly encountered in superimposed sedimentary basins, however, the uncertainty about the origin of the low oil saturation becomes a major factor impeding further hydrocarbon exploration. Routine core analysis, (fluorescence) thin section, scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) measurements were used to understand the characteristics and formation mechanisms of the low oil saturation reservoirs in the Paleogene Dongying Formation in the Nanpu sag, Bohai Bay Basin, East China. Irreducible water saturation was determined from sealed coring oil saturation testing and NMR logs. Wide ranges of porosity and permeability were observed, and the samples with moderate reservoir quality have the best oil bearing property. Low oil saturation oil layers are characterized by low oil saturation ( 40%), with only oil being produced whereas no water or only minor amounts of water being produced. The low oil saturation oil-water reservoirs refer to the low oil saturation layers in which both oil and water will be produced during oil testing. Irreducible water saturation increases with total clay content, with the authigenic clays (kaolinite, illite and mixed layer illite/smectite) blocking pore spaces, and resulting in high irreducible water saturations. Fluorescence thin sections combined with NMR measurements show that the NMR T2 (transversal relaxation time) distribution is uni-modal, with large intergranular pores being rare. Almost the entire pore-size range is oil bearing for the low oil saturation oil reservoirs. The large intergranular pores are fluorescence-free, while the intragranular dissolution pores and micropores emit fluorescence in the low oil saturation oil-water reservoirs. The NMR T2 distribution of low oil saturation oil-water reservoirs is bi-modal and right-skewed, and the main oil-bearing NMR pore size distribution ranges from 0.1 to 100 ms. High irreducible water content was encountered in the low oil saturation oil reservoirs and low oil saturation oil-water reservoirs, and only part of the large intergranular pores are oil saturated, and in some cases only the intragranular pores are saturated with oils forming low oil saturation oil reservoirs. The results help improve the knowledge of characteristics and formation of the low oil saturation oil layers, and could provide insights in enhancing oil recovery.

The study on mixed depositional reservoirs is widely attended in recent years. However, the mixed depositional reservoirs are generally characterized by complex pore structure, which is caused by strong heterogeneity, complex mineral compositions, and varying pore sizes, presenting a major challenge to describe the difference in pore structure between different samples. To address this challenge, the pore structure of mixed depositional reservoirs was evaluated by the fractal dimensions, and the influences of various mineral compositions on pore structure were analyzed. The fractal dimensions derived from NMR measurements or NMR logging data can be divided into two segments at T 2cutoff values, representing different fractal values and characteristics of pore structure. For the E 3 2 Formation in Yingxi field, the fractal dimension of movable fluid pores ranges from 2.628 to 2.917 (average 2.765), whereas the bound fluid pore systems are not following the fractal theory. Meanwhile, the fractal dimensions show a negative relationship with movable fluid porosity and permeability. The effects of various mineral compositions on fractal laws of the pore networks are different. Fractal dimension increases with the increases of clay mineral contents, and the decrease of dolomite content, while the effect of calcite content on fractal laws of the pore system is uncertain, and quartz from different genetic type represents different effect on fractal dimensions. This study is contributed for petroleum exploitation in mixed depositional reservoirs and shows that the fractal dimension can comprehensively indicate the complexity of the pore structure in mixed depositional reservoirs.

The diamond-like structured compounds with intrinsically low lattice thermal conductivity form a class of promising thermoelectric materials. Despite the stride of developing high performance p -type diamond-like materials, the report of thermoelectric study of n -type diamond-like materials is scarce. Here, we report thermoelectric study of Zn-doped n -type AgIn 5 Se 8 with the emphases on the underlying mechanism of electrical conduction and low lattice thermal conductivity. Specifically, we found that 1) the low lattice thermal conductivity was related to the low speed of sound, low-energy Einstein modes arising from the weak Ag1-Se2 and In2-Se1 bonds, and anharmonicity arising from the distorted Se1-In2-Se1 tetrahedra at high temperatures; 2) a temperature-driven transition occurred in the electrical conduction from variable range hopping (VRH) to band conduction; 3) Zn doping regulated the carrier concentration and enhanced the electronic density of states, thereby yielding a zT value of 0.60 at 880 K in the 2% Zn-doped AgIn 5 Se 8 sample. The derived zT value is promising among the n -type diamond-like structured compounds.

The Lower Cretaceous Bashijiqike Formation in Kuqa depression belongs to a continental red bed sandstone with poor reservoir quality, and is deeply buried to 5.5–7.0 km but some successions can host porosity >10% and permeability larger than 10 mD. Carbonate cements are important pore-filling constituents, and they control the reservoir quality and heterogeneity of Bashijiqike sandstones. Red hematite-bearing grain-coating clay minerals inhibit the pore occluding quartz cements and preserve intergranular pores. Here we investigate the ability of grain-coating clays to inhibit carbonate cements. Thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), and cathode luminescence (CL) analysis were performed to investigate the petrography, pore systems, diagenesis and diagenetic minerals of the red bed sandstones. The results show the hematite-bearing grain coatings give the ‘‘red bed’’ colors of the sandstones. The sandstones are heavily mechanically compacted, and the predominant pore-filling cements include carbonates and clay minerals, while quartz cements are volumetrically not important in reducing porosity. The grain-coating clays are mainly hematite-bearing mixed-layer illite and smectite. The paragenetic sequences of various types and generations of diagenetic events were reconstructed. Sandstones containing effective mixed-layer illite and smectite coatings, in which the intergranular pores can be preserved, have high porosities. Carbonate cement is never found in sandstones with effective grain coating clays, and carbonate cement precipitates where there are no sufficiently thick and continuous grain coats. The clay coatings retard or inhibit eogenetic calcite cements and progressively restrict late-stage carbonate (dolomite) cementation during burial. The hematite-bearing grain-coating clays help the red bed sandstones retain good reservoir quality at great depths.

Hydrocarbon-bearing zone identification of tight reservoirs plays a crucial role in hydrocarbon exploration and development. However, tight carbonate reservoirs are generally characterized by complex lithology, low porosity, strong heterogeneity, and weak fluid logging responses, which present a major challenge to detect hydrocarbon-bearing zones using conventional methods. To address this challenge, this paper develops a new method defined as Rwa spectrum, taking advantage of the high vertical resolution and borehole coverage of the image logs. The Rwa spectra can be derived from the histogram distribution of the apparent resistivity values of formation water (Rwa) in a sliding window, combining the Simandoux equation and the triple-porosity model. The results show that a very broad Rwa spectrum with long tails corresponds to hydrocarbon-bearing zones, and the peak shape of it is flat. In contrast, the narrow Rwa spectrum corresponds to water-bearing zones, and the peak shape of it is a sharp spike. Furthermore, two Rwa spectrum parameters, namely AVERAGE (reflects the size of main peak values) and VARIANCE (reflects shape changes of the Rwa spectra) are defined to quantificationally detect hydrocarbon-bearing zones. For oil zones in Yingxi field, the AVERAGE had a value higher than 10 and the VARIANCE was higher than 10. And for water zones, the AVERAGE had a value lower than 4.5 and the VARIANCE was lower than 5. The resistivity values decrease linearly with the increase in pyrite content of the reservoirs of high pyrite content, which disturbs the response to resistivity values from different fluid types (oil, gas or water). Hence, this method is suitable for the formation of no or little pyrite contents (lower than 0.2), and the case where the salinity value of drilling mud is similar to that of formation water. Moreover, the method has been validated by production test data, providing unusual perspectives on the identification of fluid types in tight carbonate reservoirs.

Knowledge of the state of the in-situ stress field provides important insights into the petroleum engineering and geology. The in-situ stress orientation and magnitudes in the high and steep structure of Lower Cretaceous Bashijiqike Formation in Kuqa Depression were analyzed based on well log calculations, and the impacts of in-situ stress field on reservoir quality (macroscopic reservoir properties and microscopic pore structure as well as fracture aperture) were investigated. The maximum horizontal stress (SHmax) orientation was determined as nearly north-south according to the image log derived drilling induced fractures and borehole breakouts. The vertical stress (Sv), SHmax, and minimum horizontal stress (Shmin) magnitudes were calculated via well logs. The result reveals a dominant strike-slip stress regime (SHmax > Sv > Shmin) in the Bashijiqike Formation in the Kuqa Depression. The Sv at the depth ranging from 5000 to 7100 m is 150–180 MPa, and horizontal stresses (SHmax and Shmin) vary significantly from 130 to 210 MPa. The horizontal stress difference (Δσ) is in the range from 40 to 70 MPa, and fluid overpressures are commonly encountered. The effective stress (σe) has a positive relationship with the Δσ when the Δσ is less than 50 MPa. Intergranular pores can be preserved in layers with low Δσ values. The microscopic pore structure will be complex, and macroscopic reservoir quality will be poor with the increasing Δσ values. In addition, fractures are mainly corresponding with the layers where the Δσ value is low, and the fracture aperture and porosity decreased significantly with the effective stress σe. By determining the magnitude and orientation of in-situ stresses around the wellbore, insights can be provided into the wellbore instability, optimum drilling trajectories and reservoir quality evaluation.

The lithology, mineralogy, texture, pore systems, and diagenesis of the Eocene–Oligocene Suweiyi Formation sandstones in Dina 2 Gasfield of Kuqa depression were investigated by integrating thin sections, scanning electron microscope (SEM) images with X-ray Diffraction and routine core analysis. The results reveal that carbonates and clay minerals are the dominant pore-filling constituents, while quartz cements and evaporate minerals occur in only minor amounts. Compaction played an important role in reducing intergranular porosity, especially in the clay-rich or poorly sorted successions. Framework grains dissolution greatly enhance total porosity. The pore systems consist of intergranular and intragraular dissolution porosity, micropores and minor intergranular pores. Four diagenetic facies are identified according to lithologic characteristics, diagenesis, as well as diagenetic minerals, and they are: (1) tightly compacted facies (high degree of compaction but low degree of cementation and dissolution); (2) carbonate (calcite) cemented facies; (3) clay mineral (illite and mixed-layer illite/smectite) filling facies; and (4) dissolution (of framework grains) facies. Diagenetic facies are correlated with the conventional well logs, and the well log expressions for diagenetic facies are summarized, then the diagenetic facies in uncored intervals and wells can be predicted based on the qualitative well log characteristics. Image logs were used to derive the porosity spectrum (porosity distribution histogram) by applying the typical Archie's formula to the flushed zone. Then the porosity spectrum is integrated with the conventional logs to predict the diagenetic facies, and the results can be evidenced by thin section observation, and SEM analysis. Dissolution facies, which has the highest reservoir quality, tend to have bi-modal porosity spectrum, and the porosity spectrum is very broad or even contains tail distributions. In contrast, the porosity spectrum of the carbonate cemented facies and tightly compacted facies are narrow and dominantly of uni-modal behaviors, indicating the absences of large pores and a poor reservoir quality. The porosity spectrum of clay mineral filling facies can be bi-modal or uni-modal, but the porosity spectrum is narrow and contains no tail distributions. The diagenetic facies and reservoir quality in sandstones can be predicted through correlating the diagenetic facies to conventional well logs integrated with image logs.

The Majiagou Formation is an important gas-bearing stratigraphic unit in the Ordos basin of west China. The highly complex lithology and heterogeneous pore systems make it difficult to predict the reservoir quality via petrophysical and image logs. This study investigates the lithology, pore systems and well log responses of the Majiagou Formation Member 5 (Ma 5) carbonate reservoirs using a comprehensive analysis of cores, thin sections, routine core analysis, conventional and porosity spectrum derived from image logs. The results show that the lithologies of the Ma 5 are dominantly of mud-sized to silt-sized crystalline dolomite, and there are some dolomites containing gypsums mudstones and limestone. The pore systems include vugs, intercrystalline pores, dissolution pores and microfractures. The vuggy dolomites and the fractured dolomites are the best quality reservoir rocks, and the mud-sized to silt-sized crystalline dolomites containing intercrystalline pores are good quality reservoirs with high porosity and permeability. Open fractured zones are recognized as dark sinusoidal waves, and the vuggy dolomites can be recognized by the dark spots on the image logs. However, the fractured and vuggy dolomites are only occasionally detected, and most of the dolomite reservoirs in Ma 5 contain only intercrystalline pores, which are difficult to be recognized by image logs. In addition, good quality reservoirs have very similar log responses (low natural gamma-ray (GR), low-moderate bulk density (DEN), and moderate-high resistivity) with the poor reservoir quality intervals. By applying the Archie's formula to the flushed zone, a total of 150 porosity curves can be obtained from the XRMI image logs. Then the porosity spectrum is derived from the histogram of porosity distribution for a certain interpretation interval. The best quality reservoir rocks (fractured or vuggy dolomites) have very broad porosity spectrums with long tails due to the presence of vugs and fractures. The abundance of intercrystalline pores containing in the mud-sized to silt-sized crystalline dolomites also result in the broad porosity spectrums without any tails. In contrast, the very narrow porosity spectrums correspond to the poor reservoir quality intervals. The interpretation results are verified by core observations and thin section analysis. By using the porosity spectrum analysis derived from the image logs, the reservoir quality can be predicted. The results can help improve the understanding and prediction of the reservoir quality in carbonates using well logs.

Borehole electrical image log with core-like presentation is an efficient way to conduct sedimentary description in the subsurface. The key is to set up a series of geological diagnostic criteria. The subsurface Lower Cretaceous Bashijiqike Formation in the Kelasu belt, Kuqa Depression, described as a sedimentary facies of braided river-delta front, has measured a mass of borehole image logs and open-hole logs at depths more than 6000 m. Combined with comparative outcrops, limited cores and thin sections, high-quality borehole images were fine calibrated to reveal their sedimentary details, with the aim of subtle sedimentary interpretation in the uncored intervals. The image elements all have corresponding geological indications. The lithologies are interpreted including mudstones, siltstones, fine- and medium sandstones and conglomerates, and the sedimentary structures are interpreted in terms of various bedding types, scoured surface and stacking modes. Thus, interdistributary bay, sandy or conglomerate subaqueous distributary channel and channel mouth bar are interpreted based on the lithologies, sedimentary structures and textures, basal and top contacts and succession variations. Furthermore, determination of paleo-current direction using borehole image logs is proposed for some time, but is far from mature and need to consider tectonic deformation settings of studied stratigraphy. Based on this, the paleo-current in the Kelasu belt is interpreted to flow southward from the Southern Tianshan to the depression during the Early Cretaceous which is consistent with the results derived from the heavy mineral analysis. However, the subaqueous distributary channels could frequently migrate locally and the paleo-current direction changed at localities with an offset angle varied between 30° and 150°. Regionally, the scale of single sand-body decreases lakeward and the sand-body may stretch at a maximum distance of 685.1 m along the flow direction. The diagnostic criteria and the workflow for borehole image interpretation in this study will have potential application to subsurface sedimentary description and guide sedimentary architecture where cores are not available.

The tight sandstones are characterized by low porosity, low permeability, complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced. Understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones. Diagenetic facies, which is the comprehensive description of the diagenesis and diagenetic minerals, determines the formation and distribution of sweet spot. By correlating the diagenetic facies to well log responses, the subsurface distribution of porosity and permeability can be predicted. However, the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task. This paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones, and establishes a model for prediction of diagenetic facies via well logs, as assessed from peer reviewed papers in the literature as well as from the authors' personal experiences. This review begins with reviewing the impacts of compaction, cementation, dissolution and various types of diagenetic minerals on reservoir quality evolution. The definition and classification schemes of diagenetic facies are then discussed, and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized. The same diagenetic facies commonly display similar compositional and textural attributes, matrix and cement, as well as porosity systems. The well log responses (GR, AC, DEN, CNL, and RT) of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections. By translating the diagenetic facies to conventional well logs, a predictable model, which can be used for subsurface reservoir quality prediction, is established. Then the theory of ECS logs is reviewed, and the application of ECS logs in diagenetic facies evaluation is discussed. At last, the quantitative characterization for various type and degree of diagenesis is reviewed, and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss, cementational porosity loss and dissolution porosity content via well logs. Correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones. This review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones.

Image logs provide important information on lithology, sedimentary textures, paleoflow directions, fractures and in situ stress analysis. Lacking of criteria used for establishing the image log facies limits the applications of image logs in sedimentary reservoir interpretation. This paper provides a thoroughgoing review focusing on the recent applications of borehole image logs for sedimentological and structural description and interpretation, and aims to establish image log facies which can provide guidelines in sedimentary reservoir interpretation. This paper firstly summarizes the principles and basic characteristics of various imaging logging tools, and then briefly introduces the pre-processing workflow of the image log data. Then the generated images are used for depth and orientation shifts of cores by calibrating individual sedimentary and structural features. Descriptive and concise image log facies are established based on combinations of image textures including dip type, dip pattern, and color scheme, and the characteristics as well as physical criteria for each individual image facies are summarized. The established image log facies are then interpreted in terms of structural and sedimentological features such as lithology, sedimentary structures, vugs, fractures and faults. The image log facies and its stacking patterns are then used to interpret the lithofacies associations by calibrating with cores and conventional logs. Natural fractures and induced fractures are recognized by image logs, and the principles of breakouts and drilling-induced fractures for in-situ stress analysis are reviewed. Then the applications of image logs in investigation of fracture attitudes and states, as well as in computation of fracture parameters are summarized. The procedures to evaluate fracture effectiveness through image logs are discussed. At last, the application of image logs for structural dip analysis is reviewed, and image logs are used for recognizing faults, fracture sets, and attitudes of stratum through the dip patterns. The basic procedures for paleocurrent reconstruction, which includes dip picking of cross beddings, structural dip determination and structural dip removal, are reviewed. Then the paleocurrent directions of the Lower Cretaceous Bashijiqike Formation in the Kuqa depression were reconstructed, which could help further understanding of the depositional systems. This review will help extend the utility of image logs in interpreting small to large -scale sedimentary and structural features, and bridges the gaps between well log analysis and sedimentary and structural interpretation.

Solid solution is an effective way to optimize thermoelectric performance because of the enhanced phonon scattering from point defect. In this article we describe the synthesis and discuss thermoelectric properties of Cu1-xAgxInTe2 solid solutions (x = 0, 0.05, 0.15, 0.30, 0.50). The effect of the substitution of Ag for Cu site on the microstructure and thermoelectric performance in CuInTe2 is investigated. The enlarged Seebeck coefficient coupled with reduced electrical conductivity is observed due to the diminished carrier concentration upon Ag substitution. Meanwhile, the lattice thermal conductivity is significantly depressed in solid solutions due to the strong phonon scattering. As a result, a zT value of 1.07 is achieved at 823 K with x = 0.05, which is a 90% improvement as compared with that of the pristine CuInTe2. These results demonstrate a valid approach to improve the thermoelectric properties of the compounds in the same family.

Laboratory measurements include porosity, permeability, high pressure mercury intrusion (HPMI), nuclear magnetic resonance (NMR) measurements and microscopic analysis of thin sections and scanning electron microscope (SEM) were used to gain insight into the nature of the pore throat structure including pore geometry, pore size distribution and pore connectivity of Bashijiqike tight gas sandstones in Keshen 5, Keshen 6, Keshen 8, Keshen 9 and Keshen 13 Wellblock of Kuqa depression. The relationships between microscopic pore structure parameters and macroscopic petrophysical behaviors were investigated by regression analysis. The results show that various types of pores with wide ranges of pore radius are observed. The pore throats are very small (commonly rapex) controls permeability in tight gas sandstones. The NMR pore size distribution is broader than the HPMI pore throat distribution. In the NMR analysis, only the pore systems connected by the relatively large pore throats should be accounted as movable, and some portion of large pores, which are not connected by effective large pore throats, are not effectively movable. The effective movable porosity is calculated by excluding those pores restricted by the tiny pore throats. The content of effective movable porosity from NMR measurements shows good correlation relationship with the porosity connected by large pore throats in HPMI analysis. Three typical types of pore structures are recognized through thin section, SEM analysis combined with the capillary curve and NMR T2 spectrum, and the microscopic and macroscopic characteristics of the three pore structures are investigated. The pore structure were comprehensively evaluated and characterized by linking NMR T2 spectrum with HPMI analysis.

It is known that metal parts can be made stronger, tougher and better wear resistance by introducing gradient microstructure. This work reports the cooling rate of melt pool induced discrepancy in microstructural gradient and element distribution during selective laser melting (SLM), thereby resulting in decrease in microhardness and wear resistance from surface to inside with a range of ∼100 μm of SLM- manufactured AlSi10Mg alloy. The cooling rate in the top surface of melt pool reaches ∼1.44 × 106 K/s, which is much higher than that at the bottom (≤1 × 103 K/s). Such a difference in cooling rate of melt pool is the main cause for forming gradient microstructure in terms of the distribution of Si particles, dendrite size, sub-grains and sub-boundaries. The variation in microstructure of SLM-produced AlSi10Mg alloy, as a result of gradient cooling rate, has a significant impact on its mechanical properties. Compared with core area, the surface area with a higher cooling rate is composed of finer Si particles, dendritic structure and more sub-boundaries, resulting in higher microhardness and greater wear resistance. The mechanism for formation of gradient microstructure and its influence on the mechanical properties are discussed, which provide new and deep insight into fabricating SLM-produced components with gradient microstructure.

Tight sandstone reservoirs typically contain a wide pore throat sizes ranging from the nano-scale to micro-scale, and have complex pore geometry and pore throat structure. Microscopic pore throat structures are the most important factors affecting the macroscopic reservoir quality and fluid flow in tight sandstones. Evaluation and characterization quantitatively the microscopic pore structures, including pore geometry, pore size distribution, and pore connectivity, are of great importance for maintaining and enhancing petroleum recovery. This paper critically reviews the pore throat structures of tight sandstones, as assessed from peer reviewed papers in the literature as well as from the authors' personal experiences, in the particular contexts of comprehensive characterization and description of the entire pore throat structure using various complementary techniques. The depositional controls and diagenetic imprints on reservoir quality and pore structure are firstly discussed. The pore systems including pore throat type, pore geometry, pore size and connectivity, which are related to the depositional attributes and diagenetic modifications, are summarized. Then the theories and procedures of various testing techniques commonly used for pore structure characterization of tight sandstones are reviewed. Additionally, the pore throat structure characteristics in tight sandstones are obtained from various techniques such as MICP, NMR, N 2 GA and XCT. Pore throat distribution and capillary parameters of tight sandstones are examined, and the relationship between pore throat size distribution and permeability is overviewed. The pore size distribution and 3D pore connectivity are evaluated from NMR and XCT analysis. The NMR spectrum is also linked to the macroscopic performance, and the pore network is determined from N 2 GA. Then fractal theory is introduced to explain the irregularity and heterogeneity of pore throat structure characteristics, and the models for fractal dimension calculation through various techniques are summarized. Lastly the integration of various techniques is encouraged to fully characterize the entire pore size spectrum in tight sandstones by considering the complex pore structures and limitations of a single experiment in pore throat structure evaluation. This review will provide important insights into the microscopic pore structure characteristics of tight sandstones, and address the gap in comprehensive and quantitative evaluation of the heterogeneity in tight sandstones with complex microscopic pore structures.

Electrical image log can be used to establish volcanic facies sequences, and thus used for reservoir interpretation, while the key is to set up available diagnostic criteria to guide lithology, structure and facies interpretation. A total of 50 datasets of borehole image logs, combined with wireline logs and cores, have been collected in the Yingcheng volcanic reservoir in the Xujiaweizi Depression, Songliao Basin, providing an opportunity for repeated image interpretation in the volcanic strata. The interpreted lithology includes rhyolite, dacite, andesite, basalt, welded ignimbrite, tuff, volcanic breccia and agglomerate, sedimentary tuff, sedimentary volcanic breccia and agglomerate. The volcanic structures are calibrated in terms of fluidal and deformed fluidal structure, vesicular and amygdaloidal structure, and massive structure. Based on the lithology and structures, volcanic facies including volcanic sedimentary facies, effusive facies, explosive facies and volcanic conduit facies, have been further determined. Layered structures of the weathered volcanic crusts are shown in borehole images and mainly developed at the top of the Yingcheng Formation. Borehole images indicate that SHmax direction in the area is consistent with the regional SHmax direction, with a preferable trending of 88°. Four sets of filled/open tectonic fractures are developed with approximately north, south, NNE and NW dipping. It infers that different volcanic facies can be well correlated between wells, and tectonic movements have a slight influence on the Yingcheng volcanic strata. The proposed diagnostic criteria and the workflow can be referred for a direct image interpretation in volcanic reservoirs or ocean drilling programs when cores are unavailable.

The Fengcheng Formation in the Mahu Sag of the Junggar Basin is composed of a set of fine-grained sedimentary rocks located under a layer of alkaline lacustrine rocks. There are alternating dolomite lamina, siltstone and organic matter laminae that show strong heterogeneity. The lamina structure determines reservoir quality and oil-bearing potential in shales. Therefore, the identification of lamina structure is a crucial basis for identifying reserves of shale oil. Identified as massive, layered and laminated, three different types of lamina structures are divided according to core observations in terms of the density of the laminae and the overlapping relationships. High-resolution processing is also performed on dynamic image log data to form slab images for recognizing the various types of lamina structures. Compared to core slab photos, it is believed that slab images offer an excellent thin-layer resolution of up to a millimeter in scale and can effectively identify the lamina structure of the shale reservoir. There are no evident beddings on the core of the massive pattern, and the slab image shows a bright or dark block pattern. There are centimeter-level felsic bands of fine silt sand on the thin-layered sedimentary fabric core, and the slice image shows a band-like pattern. A large number of millimeter-level dolomitic laminae are enriched on the core of the laminated type, and the slab image shows millimeter-level light and dark lamina. Slab images were used for the division and identification of lamina structures in a single well. Then, the relationships between the three types of lamina structures and the two-dimensional nuclear magnetic resonance logs and oil test data were recorded. The results show that massive and laminated pores are dominated by intergranular pores with low porosity and movable oil content. Therefore, only low oil flow can be obtained during an oil test. However, the layered type due to centimeter-level silty bands, T1 and T2, is bimodal with high porosity, movable oil content, and high levels of hydrocarbon production. Therefore, the optimal areas of shale reservoirs are closely related to the layered type. The more significant the proportion of layered types in shale reservoirs, the higher the quality of the reservoir. The present study is intended to identify lamina structure-controlled reservoir quality and oil accumulation and to provide insights into the exploration and development of shale oil.

AgBiSe2 is a promising n-type compound with high thermoelectric performance but suffers from a multiple structural phase transition. Here, we show the high-temperature rock salt phase can be stabilized at ambient conditions in AgBi1-xSbxSe2 solid solutions with x higher than 0.2, which is attributed to the increased configurational entropy. Moreover, the optimum increment of configurational entropy is determined by analyzing the weighted mobility and quality factor. Finally, benefiting from the intrinsically low lattice thermal conductivity and well-maintained carrier mobility, a peak zT value of 0.86 at 790 K, is attained for cubic AgBi0.8Sb0.2Se2 after bromine doping. This work highlights the importance of entropy engineering in thermoelectric performance and phase stability, providing insights into the discovery and design of environmental-friendly thermoelectrics.

In order to construct a unified permeability prediction model for multi-stage tight gas sandstones with permeability across 6 orders of magnitude and changeable porosity-permeability relationship, Bayesian regularization neural network is properly configured with core porosity, conventional logs and a few derivates of them as input items. With high accuracy and excellent generalization, it is promising to be stably and reliably popularized in the study area. The way of model construction, optimization and evaluation may provide underlying insights needed for permeability prediction of similar reservoirs and application of machine learning in reservoir evaluation.

Cu based ternary compounds with diamond-like crystal structure received intensive attentions in last decade as potential thermoelectric materials whereas the investigation of high order derivatives (e. g. I2-IV-VI3) with anion as Te is lacking due to the synthesis difficulty in conventional solid state reaction. Herein, Cu2SnTe3 has been synthesized by colloid method and its high temperature thermoelectric properties have been preliminarily explored. The electrical conductivity of pristine Cu2SnTe3 has been found as high as ~105 S m−1 owning to intrinsically high carrier concentration, which resulted in low thermoelectric performance. Thus, the pristine Cu2SnTe3 compound has been used as solid solution component to alloy with CuInTe2, which also possesses diamond-like structure but with low carrier density. The results have shown that the thermoelectric performance of CuInTe2 can be enhanced through alloying with Cu2SnTe3, primarily resulting from huge reduction in lattice thermal conductivity. The sample with nominal composition of (Cu0.96InTe2)0.97(Cu2SnTe3)0.03 has reached a maximum zT value of ~0.9 at 823 K. Our findings should shed light on design of new thermoelectric compounds in diamond-like semiconductor family.

Permeability can effectively represent the ability of fluids to flow in porous media, and is a crucial physical parameter for the exploration of unconventional oil reservoirs. In low-permeable porous media, such as tight rocks, not all pores function as fluid flow channels; meanwhile, the pore surface tends to form unevenly adsorbed water lay. To date, the two phenomena above have not been considered in previous studies on permeability estimation models. In this study, a new fractal permeability model with variable pore sizes was proposed resulting in two advancements: (1) unevenly adsorbed water lay attached to pore surfaces was considered; and (2) instead of the total pore space, the movable fluid space obtained from nuclear magnetic resonance (NMR) experiments was used as the fluid flow channels in the porous media. Helium permeability data of 26 mixed rock samples from tight oil reservoirs were used to establish the accuracy of the proposed permeability model. The results of a sensitivity analysis show that high porosity and large pore diameters play a positive role in generating high permeability in porous media. The permeability decreased with an increase in the fractal dimension of the total pore space and the tortuosity fractal dimension of the total pore space and movable fluid space, whereas it first decreased and then increased as the fractal dimension of the movable fluid space increased. Furthermore, the proposed model indicates that the movable fluid space and unevenly adsorbed water lay greatly influence the fluid flow, specifically at lower permeabilities (K＜0.1 mD), while the influence of the unevenness of the adsorbed water lay on fluid flow is negligible at high permeabilities. Overall, the accuracy of the permeability estimation of the proposed model is reliable both in low-permeable and conventional porous media, and can be effectively applied to unconventional oil reservoirs.

In this study, the effect of Cu vacancy on the thermoelectric performance of Cu 1- x InTe 2 is reported, where x is 0, 0.04, 0.06, 0.08 and 0.10. Cu vacancy can yield excess holes lifting the carrier density of CuInTe 2 , which is an intrinsic p-type semiconductor. Meanwhile, the mass fluctuation caused by Cu vacancy attributes to the enhanced point defects phonon scattering, resulting in a reduced lattice thermal conductivity. The optimum Cu vacancy content is found to be 0.04, attaining a maximum zT value of 0.83 at 820 K. Meanwhile, there is a 50% enhancement compared to that of pure sample which arises from the large power factor and the relatively low thermal conductivity. Our result indicates the great potential of Cu 1- x InTe 2 for thermoelectric application at middle-temperature.

The image logs played a key role in interpreting the lithology and sedimentary structures of uncored units. An integrated analysis of the borehole images and open-hole logs, which are calibrated with core observations, is conducted to reveal the detailed sedimentary characteristics of the Upper Triassic Xujiahe Formation in the Central Sichuan Basin. To establish borehole image interpretation guidelines, the interpretations of sedimentary textures and lithology from cores and outcrops are calibrated with borehole images and conventional logs. Lithologies in the Xujiahe Formation include conglomerates, fine to medium-grained sandstones, siltstones, mudstones and coals. Sedimentary structures in terms of bedding, scour surface and stacking style of beds are interpreted from the image and open-hole logs. Depositional microfacies are defined on the basis of grain size and sediment texture, sedimentary structures, thickness, basal and upper contacts derived from core observations, openhole logs and image logs. The Xujiahe Formation sandstones in Central Sichuan Basin are deposited in a braided delta front, of which the depositional microfacies consist of underwater distributary channel, river mouth bar, distal bar or sand sheet and underwater interdistributary bay. The depositional microfacies is predicted in a single well using a combination of openhole conventional logs, borehole images, and cores. The distributary channels, which show box-shaped or bell-shaped GR log character, are generally infilled with fine to medium-grained sandstone with massive, tabular, wedge-shaped or trough-cross-laminated bedding. Repeated fining-upwards cycles, as well as the stacked nature of individual bedsets and the presence of scour surfaces represent multistory, amalgamated, channel-fill deposits. The underwater distributary channel deposits can also be overlain by interdistributary bay mudstones, known as channel abandonment. Mouth-bar deposits, which are characterized by coarsening- up successions, infill the channels as they migrate laterally, and sometimes could be overlain by a channel deposit. The methodology has potential application to other braided delta front reservoirs with appropriate calibration and scaling.

The deeply buried (5.5–7.1 km) Lower Cretaceous Bashijiqike sandstones are important fractured reservoirs in the Kuqa depression. In these high temperature-high pressure drilling environments, oil-based muds are used to limit drilling risks and improve efficiency, making facture detection using resistivity-based image logs difficult. The maximum horizontal stress (SH max ) trends close to North-South(0–10°) based on orientations of the drilling-induced fractures and borehole breakouts. Core descriptions, thin sections and image logs used to describe the fractures in the Bashijiqike sandstone reservoirs show that opening-mode natural fractures are common, and the fractures range from fully open to sealed by calcite and clay minerals. The open fractures are dominantly steeply dipping or vertical and primarily strike north-south. Locally horizontal fractures or fractures with low angle dip are detected. We compare fracture visibility on image logs acquired in the same KS 2-2-12 key well in oil-based mud and water-based mud. FMI-HD logs successfully detect large (0.1 mm aperture) vertical fractures in oil-based mud better than OBMI image logs, and the two imaging tools have a similar ability in detecting the high dip angle fractures. Since the UBI tool is not affected by oil-based muds, most of the fractures can be picked out on UBI images. Minor negative deviations of bulk density could be observed in fractured zones, and the presence of fractures obviously causes an increase in sonic transit time. Full waveforms from DSI tools combined with electrical image logs detect fractured zones. Both the velocity and amplitude of the sonic waves are sensitive to fractures, and the fractured zones could be identified according to the attenuation of Stoneley waves. The combination of cores, image logs, and full-wave sonic logs offers comprehensive detection of fractures in oil-based mud environments.

Marine dolostones of Carboniferous Huanglong Formation constitute major gas reservoir rocks in eastern Sichuan Basin. However, the investigation with respect to sources of dolomitizing and diagenetic fluids is relatively underexplored. The current study attempts to investigate the REE characteristics of dolomites using seawater normalization standard, and therefore discusses the origins of dolomitizing and diagenetic fluids, on the basis of continuous 47.33-m-long core samples from the second member of Huanglong Formation (C 2 h 2 ) in eastern Sichuan Basin. Low Th, Sc, and Hf concentrations (0.791 × 10 −6 , 4.751 × 10 −6 , and 0.214 × 10 −6 , respectively), random correlation between total REE concentration (ΣREE) and Fe or Mn abundance, and seawater-like Y/Ho ratios (mean value of 45.612) indicate that the carbonate samples are valid for REE analysis. Based on petrographic characteristics, four dolomite types are identified, including micritic-sized dolomite (type Dol-1), fine-to medium-sized dolomite (type Dol-2), medium-to coarse-sized dolomite (type Dol-3), and coarse-to giant-sized saddle dolomite (type Dol-4). Dol-1 dolomites, characterized by positive Ce anomaly (mean value of 6.398), light REE (LREE) enrichment, and heavy REE (HREE) depletion with mean LREE/HREE ratio of 12.657, show micritic calcite-like REE patterns, indicating seawater origin of their dolomitizing fluids. Dol-1 dolomites were formed in sabkha environment whereas the dolomitizing fluids originated from evaporative brine water due to their micritic crystal sizes and tight lithology. Dol-2 dolomites, particularly subtype Dol-2a barely developing vuggy porosity, also show micritic calcite-like REE patterns, suggesting their dolomitizing fluids were seawater or seawater-derived fluids. This inference is confirmed by low Fe and Mn concentrations, which range from 651 μg/g to 1018 μg/g (mean value of 863 μg/g) and 65 μg/g to 167 μg/g (mean value of 105 μg/g), respectively, whereas homogenization temperatures (T h , mean value of 103 °C) indicate that Dol-2 dolomites were formed under burial environment. Dol-3 dolomites, in form of cements of Dol-2 dolomites, show similar REE patterns to their host minerals (i.e., Dol-2 dolomites), indicating their parent source was possibly derived from Dol-2 dolomites. Dol-3 dolomites have high Fe and Mn concentrations with mean values of 3346 μg/g (ranging from 2897 μg/g to 3856 μg/g) and 236 μg/g (ranging from 178 μg/g to 287 μg/g), respectively, indicating the involvement of meteoric water. Meanwhile, it confirms that the dissolution in Dol-2 dolomites was caused by meteoric water leaching. Positive Eu anomalies (mean value of 1.406) in Dol-4 dolomites, coupled with high homogenization temperatures (mean value of 314 °C), suggest that Dol-4 dolomites precipitated from hydrothermal fluids. High Fe and Mn concentrations (mean values of 2521 μg/g and 193 μg/g, respectively) in Dol-4 dolomites likely results from interactions of hydrothermal fluids with deep burial clastic rocks.

Understanding diagenetic heterogeneity in tight sandstone reservoirs is vital for hydrocarbon exploration. As a typical tight sandstone reservoir, the seventh unit of the Upper Triassic Yanchang Formation in the Ordos Basin (Chang 7 unit), central China, is an important oil-producing interval. Results of helium porosity and permeability and petrographic assessment from thin sections, X-ray diffraction, scanning electron microscopy and cathodoluminescence analysis demonstrate that the sandstones have encountered various diagenetic processes encompassing mechanical and chemical compaction, cementation by carbonate, quartz, clay minerals, and dissolution of feldspar and lithic fragments. The sandstones comprise silt-to medium-grained lithic arkoses to feldspathic litharenites and litharenites, which have low porosity (0.5%–13.6%, with an average of 6.8%) and low permeability (0.009 × 10 −3 μm 2 to 1.818 × 10 −3 μm 2 , with an average of 0.106 × 10 −3 μm 2 ). This study suggests that diagenetic facies identified from petrographic observations can be up-scaled by correlation with wire-line log responses, which can facilitate prediction of reservoir quality at a field-scale. Four diagenetic facies are determined based on petrographic features including intensity of compaction, cement types and amounts, and degree of dissolution. Unstable and labile components of sandstones can be identified by low bulk density and low gamma ray log values, and those sandstones show the highest reservoir quality. Tightly compacted sandstones/siltstones, which tend to have high gamma ray readings and relatively high bulk density values, show the poorest reservoir quality. A model based on principal component analysis (PCA) is built and show better prediction of diagenetic facies than biplots of well logs. The model is validated by blind testing log-predicted diagenetic facies against petrographic features from core samples of the Upper Triassic Yanchang Formation in the Ordos Basin, which indicates it is a helpful predictive model.

We investigate the anisotropy in thermoelectric transport properties of pristine and self-doped InTe after spark plasma sintering and ascribe the observed weak anisotropy to the lack in orientation preference of investigated specimens as characterized by the scanning electron microscope. Then, the effect of Cu/Na doping on the transport properties of InTe is discussed for comparison, which suggests Cu doping is more favorable for keeping decent carrier mobility than Na doping and In-deficiency. Such difference is qualitatively explained by the large electronic affinity of Cu as compared to Na, which can effectively weaken the Coulomb scattering for charge carriers. Finally, a maximum figure of merit zT of about 0.73 at 730 K is obtained for the compound with the nominal composition of In0.99Cu0.01Te, measured parallel to the pressing direction, which can be attributed to the enhanced carrier concentration and well-maintained mobility compared to the pristine specimen. Furthermore, the Cu-doped specimen shows a superior average zT about 0.34, more than 35% enhancement than that for both Na-doped and self-doped InTe compounds. Our results should provide a guidance for selecting dopants for thermoelectric materials that possess strong ionized-impurity scattering character.

Present-day stress state is significant for petroleum industry and prediction of stress-related geohazards. The Kelasu Belt, located between Southern Tianshan and the bank-land of the Tarim Basin, is a main gas source in China and is extremely active during Himalayan movement. Predicting the in-situ stress of the BSJQK Formation in the Kelasu Belt is difficult due to the ultra-deep tight sandstone reservoir (5500–8500 m depth), with pervasively developed fractures, surrounded by multi-detachment layers and complicated structural association. In this study, we first analyzed the present-day maximum horizontal stress in the BSJQK Formation using imaging logs (FMI-HD, OBMI, EI and CBIL), then carried out the fracture interpretation based on core-image calibration, finally evaluated their hydraulic conductivity integrating well testing, petrophysical experiments and logging interpretation. The average S Hmax orientation in wells B, C, D and E in the Kelasu Belt correspond to 124.76°N (±8.5°), 92.86°N (±4.3°), 143.28°N (±7.1°) and 180.89°N (±4.5°), respectively, which coincides well with the result derived from the focal mechanism solution. The stratigraphic attitude and boundary structure may control the variation of S Hmax orientation. Fracture attitude in wells B, C, D and E correspond to 70°/26°N, 54°/346°N, 81°/239°N and 76°/253°N, respectively and intersect S Hmax at an angle less than 29°. Fracture could increase formation permeability with 1–3 order of magnitudes and provides the main channel for gas migration. Furthermore, the calculation of “Gas Productivity Index per Meter” indicates that fracture density is closely related with gas productivity, which will guide the next fracturing intervals. The N-S or NEE-SWW could be the preferable orientations for drilling trajectory design of horizontal wells.

Hydrocarbons reserved in the contact metamorphic zones of magmatic rocks are found in rift basins as a new type of unconventional resources. However, their reservoir characteristics are relatively underexplored. On the basis of core samples, thin sections, and analysis data available, this study investigates the reservoir properties of contact metamorphic zones of the diabase from the northern slope of the Gaoyou Sag, Subei Basin in eastern China. The factors that control the reservoir quality are also investigated. In the studied area, diabase intrusion exerts significant influences on contact sedimentary rocks (including contact mudstones and sandstones) as hydrocarbon reservoirs. After contact metamorphism, the impermeable mudstones are altered into permeable metamudstones, including intermediate-metamorphosed hornfelses and low degree-metamorphosed slates. Various types of reservoir spaces, including structural fractures, hydrothermal microfissures, contraction microfissures, cleavage microfissures, intercrystalline micropores, and dissolved micropores, are created in metamudstones. Among them, numerous fractures and microfissures are the main factors of reservoir quality enhancement. Contact sandstones are altered into metasandstones, whose reservoir space types are similar to those of unaffected sandstones. The reservoir spaces mainly include primary intergranular pores, dissolved intergranular pores, dissolved intragranular pores, moldic pores, ultralarge pores, and dissolved micropores. The formation of reservoir spaces in contact metamudstones is mainly controlled by diabase intrusion, and it is not influenced by burial compaction. The controlling mechanisms of this formation include physical fracturing, hydrothermal activity, dissolution, and cooling contraction. The reservoir quality of contact metasandstones is primarily controlled by lithofacies and diagenesis before intrusion. However, later-stage diabase intrusion also exerts considerable control on reservoir quality by causing physical pressure, dissolution, and cementation. Although dissolution increases porosity moderately, it insufficiently compensates for the porosity reduction caused by physical pressure and cementation. Thus, the reservoir quality of contact metasandstones is generally decreased by diabase intrusion. A comprehensive reservoir model of contact metamorphic rocks is proposed based on the preceding analysis. This model serves to predict the distribution of high-quality reservoir in contact metamorphic rocks in the studied area. It can also be applicable to other formations of similar intrusive background.

High-quality carbonate gas reservoirs of the Upper Permian Changxing Formation (P2ch) in the eastern Sichuan Basin are mainly dolostones. Subsurface core samples from the Longhui-Tieshan area were studied to determine the origins of dolomitizing fluids and interpret porosity evolution during dolomitization. Petrographically, two dolomite types were identified, including micritic to fine-sized dolomites (type 1) and fine-to coarse-sized sucrosic dolomites (type 2). The type 1 dolomites, characterized by micritic crystals ( 500 μm) and high Mg/Ca order degrees (mean value of 0.787). Low Fe and Mn concentrations (163 ppm and 69 ppm, respectively), high homogenization temperatures (60 °C–200 °C), depleted δ18O values (mean value of −5.14‰), and Sr isotope compositions (mean value of 0.707643), collectively suggest that the dolomitizing fluid of type 2 dolomites was likely derived from buried, imprisoned brine water closely associated with Early Triassic seawater but unrelated to meteoric water. During the first stage of porosity evolution (i.e., stage A), carbonate porosity was slightly decreased by dolomitizing fluids preferentially replacing micritic components and CO32− ions involvement. During the second stage (i.e., stage B), carbonate porosity was slightly increased because molecular replacement occurred under an environment with insufficient CO32− ions. During the advanced stage (i.e., stage C), dolomitization was intensively weakened because of CO32− ions depletion, yet the acidic dissolution and structural movements produced considerable pores and fractures, forming high-quality reservoirs. Type 1 dolomites are volumetrically minor and have no reservoir potential, effective reservoirs are closely associated with type 2 dolomites. A burial dolomitization model of type 2 dolomites is proposed based on the previous analyses. Dolomitizing fluids moved downward through open faults and unconformities into P2ch carbonates. Potentially high-quality reservoirs likely occur at locations close to dolomitizing fluid conduits.

The Chang 7 tight oil reservoirs are important oil exploration targets in the Ordos basin. The reservoirs are generally characterized by low porosity, low permeability and strong microscopic heterogeneity. Mineralogical, petrographic, and geochemical analyses have been used to investigate the type and degree of diagenesis and diagenetic history of Chang 7 tight oil reservoirs. The influences of composition, texture and diagenesis on reservoir quality were also discussed in this article. Diagenesis of the Chang 7 tight oil reservoirs was mainly composed of mechanical compaction, grain dissolution and cementation by quartz, carbonates and various clay minerals. Reduction of porosity by mechanical compaction was more significant than by cementation. Eodiagenesis mainly includes (1) mechanical compaction and mechanically infiltrated clays; (2) cementation by calcite, pyrite, and clay minerals; and (3) leaching of feldspars. Mesodiagenesis mainly includes (1) further mechanical compaction; (2) cementation by late stage carbonates; (2) formation of illite and mixed-layered illite-smectite; (3) quartz cements; (4) dissolution of feldspars. The porosity was decreased by compaction and cementation and then increased by dissolution of the framework grains. Primary porosity is higher in sandstones with abundant detrital quartz. Secondary dissolution pores are mainly associated with those feldspar-rich samples. Sandstones which have undergone the most feldspar dissolution are the cleaner (abundant in both detrital quartz and feldspar), better sorted, and coarser-grained samples. Reservoir quality of Chang 7 tight oil reservoirs is also largely controlled by pore occluding cements. The composition and texture have played an important role on intergranular volume and subsequent diagenetic modifications of the Chang 7 tight oil reservoirs. Good quality reservoir intervals are characterized by fine-grained, moderately-well sorted with high percentages of detrital quartz and feldspar but low content of detrital clay and cements.