Three-dimensional Digital Core Research Articles

Simulation of nuclear magnetic resonance response based on the high-resolution three-dimensional digital core

Simulation of nuclear magnetic resonance response based on the high-resolution three-dimensional digital core

Characterization and Quantitative Assessment of Shale Fracture Characteristics and Fracability Based on a Three-Dimensional Digital Core

At present, assessment techniques for the fracability of shale reservoirs, which rely on the formation of an effective fracture network, are scarce. Hence, in order to assess the fracability, it is critical to establish a quantitative correlation between the pattern of fracture distribution after fracture and fracability. The present investigation utilizes three-dimensional digital core technology and triaxial compression experiments to simulate the fracturing process in typical domestic shale reservoir cores. In addition to utilizing the maximum ball algorithm to extract fracture images, a number of other techniques are employed to compute the spatial quantitative parameters of the fractures, including least squares fitting, image tracking algorithms, and three-dimensional image topology algorithms. The introduction of the notion of three-dimensional fracture complexity serves to delineate the degree of successful fracture network formation subsequent to fracturing. A quantitative fracability characterization model is developed by integrating the constraints of fracture network formation potential and fragmentation potential. The results of this study show that the quantitative characterization of the characteristic parameters of cracks can be achieved by establishing a method for extracting crack information as well as parameters after core compression and completing the construction of a three-dimensional complexity characterization model. Meanwhile, the three-dimensional post-compression fracture image validation shows that the core fracturability index can better reflect the actual fracturing situation, which is in line with the microseismic monitoring results, and significantly improves the accuracy of fracturability characterization, which is an important guideline for the fracturing design of shale gas reservoirs.

Study on oil seepage mechanisms in lamellar shale by using the lattice Boltzmann method

The shale oil and gas resources in the world are rich and are an important part of unconventional oil and gas resources. In this paper, firstly, by comprehensively using CT scanning technology, the three-dimensional pore-fracture structure characteristics of shale core samples of different sizes is characterized, and a three-dimensional digital core is established; Secondly, SEM and FIB-SEM techniques are systematically used to describe the microstructure and fracture network development characteristics of shale matrix pores and fractures, and a three-dimensional pore and fracture network model is established; Thirdly, Combined with LBZ simulation method, the mechanism of two-phase fluid transport in shale cross-scale fracture network is explored. Results show that: (a) The relatively dispersed mesopores and macropores in space constitute the main storage space of methane. Some pores in the study area of shale samples have good connectivity, and some samples only have connected pores in the study area of their magnification. (b) A large number of intergranular pores and fissures developed together with the intergranular pores of clay minerals, forming a good network connection system between microscopic pores in laminated shale. (c) when the hydrophilic mineral proportion is increased from 30% to 70%, the relative permeability of oil phase at water saturations of 20%, 40% and 60% has an increase of 6.8%, 7.8% and 4.2%, respectively, and the relative permeability of water phase at water saturations of 20%, 40% and 60% has a decrease of 1.8%, 2.6% and 6.5%, respectively. (d) When the oil phase contact angle is increased from 30° to 70°, the relative permeability of oil phase at water saturations of 20%, 40% and 60% has an increase of 1.9%, 2.7% and 2.2%, respectively, and the relative permeability of water phase at water saturations of 20%, 40% and 60% has a decrease of 1.2%, 2.1% and 3.5%, respectively.

Deep learning method of stochastic reconstruction of three-dimensional digital cores from a two-dimensional image.

Digital cores can characterize the true internal structure of rocks at the pore scale. This method has become one of the most effective ways to quantitatively analyze the pore structure and other properties of digital cores in rock physics and petroleum science. Deep learning can precisely extract features from training images for a rapid reconstruction of digital cores. Usually, the reconstruction of three-dimensional (3D) digital cores is performed by optimization using generative adversarial networks. The training data required for the 3D reconstruction are 3D training images. In practice, two-dimensional (2D) imaging devices are widely used because they can achieve faster imaging, higher resolution, and easier identification of different rock phases, so replacing 3D images with 2D ones avoids the difficulty of acquiring 3D images. In this paper, we propose a method, named EWGAN-GP, for the reconstruction of 3D structures from a 2D image. Our proposed method includes an encoder, a generator, and three discriminators. The main purpose of the encoder is to extract statistical features of a 2D image. The generator extends the extracted features into 3D data structures. Meanwhile, the three discriminators have been designed to gauge the similarity of morphological characteristics between cross sectionsof the reconstructed 3D structure and the real image. The porosity loss function is used to control the distribution of each phase in general. In the entire optimization process, a strategy using Wasserstein distance with gradient penalty makes the convergence of the training process faster and the reconstruction result more stable; it also avoids the problems of gradient disappearance and mode collapse. Finally, the reconstructed 3D structure and the target 3D structure are visualized to ascertain their similar morphologies. The morphological parameter indicators of the reconstructed 3D structure were consistent with those of the target 3D structure. The microstructure parameters of the 3D structure were also compared and analyzed. The proposed method can achieve accurate and stable 3D reconstruction compared with classical stochastic methods of image reconstruction.

Modeling of multi-mineral-component digital core based on Res-Unet

Abstract As the exploration of oil and gas moves further into less conventional reservoirs, effective methods are required for the fine evaluation of complex formations, particularly digital core models with multiple mineral components. The current technology cannot directly produce digital core images with multiple minerals. Therefore, image segmentation has been widely used to create digital multi-mineral core images from computed tomography (CT) images. The commonly used image segmentation methods do not provide satisfactory CT images of complex rock formations. Consequently, deep learning algorithms have been successfully applied for image segmentation. In this paper, a novel method is proposed to develop an accurate digital core model with multiple mineral components based on the Res-Unet neural network. CT images of glutenite and the corresponding results of quantitative evaluation of minerals by scanning electron microscopy are used as a training dataset for the automatic segmentation of CT core images. The used quantitative metrics show that compared with the multi-threshold and U-Net segmentation methods, the Res-Unet network leads to better results of mineral morphology and distribution recognition. Finally, it is demonstrated that the proposed Res-Unet-based segmentation model is an effective tool for creating three-dimensional digital core models with multiple mineral components.

Study on the Quantitative Characterization and Heterogeneity of Pore Structure in Deep Ultra-High Pressure Tight Glutenite Reservoirs

The precise characterization of a tight glutenite reservoir’s microscopic pore structure is essential for its efficient development. However, it is difficult to accurately evaluate using a single method, and its microscopic heterogeneity is not fully understood. In this study, a combination of X-ray diffraction, casting thin section observations, scanning electron microscopy, high-pressure mercury injection, constant-speed mercury injection, X-ray computed tomography, and the advanced mathematical algorithms in the AVIZO 8.0 visualization software was used to construct the three-dimensional digital core of a glutenite reservoir at the study site, and the parameters of the pore network model were extracted. The overall microscopic pore structure characteristics were quantitatively investigated from multiple scales. Based on this, the mineral quantitative evaluation system (QEMSCAN) examined the microscopic heterogeneity of the glutenite reservoir and its impact on seepage. The results show that the glutenite reservoir in the study block can be classified into three categories based on lithology and capillary pressure curve characteristics. The type I reservoir samples have large and wide pore throats, low threshold pressure, and high reservoir quality; type II reservoir samples are characterized by medium-sized pore throat, medium threshold pressure, and moderate reservoir quality; and the small and narrow pore throat, high threshold pressure, and poor reservoir quality are characteristics of type III reservoir samples. The various pore throat types and mineral distributions are due to the differences in dissolution, compaction, and cementation. The continuous sheet pores have good connectivity, which is related to the interconnection of primary intergranular pores and strip fractures, while the connectivity of isolated pores is significantly poor, which is related to the development of intragranular dissolved pores and intercrystalline pores. This suggests the deterioration of physical properties and pore throat connectivity, reduced average pore radius, and decreased pore sorting as decreasing permeability. The tight glutenite pores range in size from 5 nm to 80 μm and primarily feature Gaussian and bimodal distribution patterns, and submicron–micron pores contribute more to seepage. The effective pores were found to be attributed to the slowing effect of abnormally high pressure on the vertical stress, and the protective effect was positively correlated with the high-pressure strength. Notably, there is strong microscopic heterogeneity in the distribution of the reservoir matrix minerals and the pore throat size. As a result, the injected fluid easily flows along the preferential seepage channel with pore development and connectivity. This study provides new insights into the exploration and development of similar tight reservoirs.

The investigation of microporous structure and fluid distribution mechanism in tight sandstone gas reservoirs: A case study on the second member of Xujiahe gas reservoirs in Yuanba area

Tight sandstone reservoir is characterized by ultra-low porosity, complex microporous structure and water residues, which shows different gas storage and transport mechanism from conventional reservoirs. Therefore, effective development of tight sandstone gas reservoirs is faced with technical challenges. Microporous structures, distribution mechanism of fluid is a basic issue in gas reservoir evaluation. In this work, we take gas reservoir in the 2nd member of Xujiahe Formation in Yuanba area as an example to analyze the microscopic feature of pore structure and fluid distribution. The three-dimensional digital core has been applied to represent the real microporous structure. Specifically, a digital core reconstruction method based on SEM and casting slice images has been proposed. Ultimately, the mechanism of distribution, mode of occurrence of water residues in tight sandstone reservoirs has been simulated and quantitatively analyzed. The results show that the water residues could been visualized and categorized into three modes, water mass in corner, water film on surface, and water column in throat. The water residues could cause dramatic influence on pore structures, active pore size could be decreased with rising residual water saturation, the magnitude falls by over 50%. In addition, grain size would affect the distribution of water residues, which shows different percentage in medium and fine sand. Pore connectivity is another characteristic factor to describe the microporous structures. In this study, cluster marking algorithm has been applied to obtain the pore connectivity in tight sandstone with different grain size. In medium sand, the pore connectivity is dramatically decreased with rising water saturation, the downward trend become slower when water saturation reaches to 60%. Compared to fine sand, the tendency variation appears when water saturation reaches to 40%. This paper provides an applicable method to reveal the micro-scale reservoir properties and fluid distribution mechanisms in tight sandstone gas reservoirs.

A method for pore-scale simulation of single-phase shale oil flow based on three-dimensional digital cores with hybrid mineral phases

The mineral properties of the pore walls have a great influence on the single-phase shale oil flow at the pore scale. In this paper, a new method is proposed for pore-scale simulation of single-phase shale oil flow based on digital cores with hybrid mineral phases. This method can identify each mineral pore wall and correspondingly consider the adsorption layer and slippage boundary condition. First, three-dimensional (3D) digital cores with hybrid mineral phases are reconstructed from two-dimensional (2D) scanning electron microscope images of a shale sample, and correspondingly the pore space is divided with computational grids. Second, a mathematical model of shale fluid flow is established based on the Navier–Stokes (N–S) equation, combined with the slip length and viscosity formula. Finally, the equations are discretized on the mesh by the finite volume method and solved by the semi-implicit method for pressure-linked equations for flow simulation of shale oil in the 3D digital cores. By applying the method, we analyze effects of total organic carbon in volume, slippage, and adsorption on the single-phase shale oil flow based on 3D digital cores with hybrid mineral phases.

Pore-scale formation damage caused by fracturing fluids in low-permeability sandy conglomerate reservoirs

Low-permeability sandy conglomerate reservoirs are inevitably vulnerable to interaction with foreign fluids, which seriously affects oil recovery. Hydraulic fracturing, which is normally achieved by squeezing high-viscosity fracturing fluids into the reservoir, is the primary method to exploit low-permeability reservoirs. Although fracturing fluids can rupture rocks and produce fractures, they also cause formation damage. Therefore, it is critical and essential to explore the formation damage caused by fracturing fluids to protect the formation and enhance oil recovery. In this paper, two types of conventional fracturing fluids (i.e. slickwater and guanidine gum gelout) were used to study the mechanisms of pore-scale formation damage, which was assisted by the three-dimensional mineral distribution reconstruction based on in-situ micro-computed tomography. During the formation damage caused by slick water, gaps at pore edges were found to be corroded and closed. In contrast, during the guanidine gum gelout-caused formation damage, the formation of flocculent deposits led to the accumulation of particles in the pores. Porosity decreases are observed in all cores flooded with fracturing fluids and distilled water. Gray-scale values of minerals in the micro-computed tomography images were identified based on the mineral distribution map determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. These gray-scale values were compared with mineral contents obtained by X-ray diffraction. Eventually, a three-dimensional digital core was established based on mineral features, and clay minerals were demonstrated to be critical in the formation damage by blocking pores and thus separating large pores into small pores. • The co-image from micro-computed tomography and SEM-EDS was found. • Three-dimensional digital core reconstruction based on mineral is realized. • Clay mineral is the key mineral causing formation damage by fracturing fluid.

Review of 3D digital core reconstruction methods for deep shale gas reservoir

Conventional digital core reconstruction methods are not suitable for deep shale gas reservoirs with low porosity and permeability, anisotropy and complex mineral composition, and conventional single resolution three-dimensional digital core structure model cannot fully describe the core structure of shale gas reservoirs of different scales. In this paper, the advantages and disadvantages of different digital core reconstruction methods are summarized by analyzing examples. It is found that MCMC core reconstruction method is more suitable for image reconstruction of 3D digital structure model core of deep shale gas reservoir in China; Finally, in view of the problems existing in conventional digital core reconstruction methods, combining CT imaging with ion beam focused electron microscopy (FIB-SEM) imaging technology, a 3D digital core structure model with multi-scale, multi-component and corresponding macro pore and micro pore of the corresponding reservoir is proposed. The micro spatial distribution structure of the model is similar to that of real shale gas reservoir core, it overcomes the difficulty that the resolution of single scale 3D digital gas reservoir core model and the micro size characteristics of gas reservoir core cannot be perfectly considered. It can not only accurately describe the micro pore space distribution structure of real core gas reservoir, but also accurately describe the macro heterogeneity of deep shale gas reservoir core.

Investigation of coal elastic properties based on digital core technology and finite element method

Rock elastic properties play an important role in the geological characteristics of reservoirs. The analysis of these properties is normally based physical experiments on rocks. However, such conventional physical experiments cannot meet actual requirements when the rock is fragile or has complex composition. With the development of computer technology and the application of micro-computed tomography scanning technology, digital rock physics technologies came into existence. In this work, micro-computed tomography was applied to obtain high-quality three-dimensional images of coal samples. Next, the image multi-threshold segmentation method was used to divide the grayscale image into three reasonable components, including mineral, organic matrix, and pores. Digital rock models with different gas saturations were established using mathematical morphology based methods. Five volume samples were selected from the original large digital rock model under different conditions of porosity, mineral, and gas saturation. Based on these three-dimensional digital cores and the finite element method, the effective elastic moduli of coal rock mass were simulated and the compressional wave velocity and shear wave velocity were computed. Results show that, in the absence of filled minerals, both bulk and shear moduli decrease with rising porosity; compressional and shear wave velocities decline, and the ratio of compressional wave velocity to shear wave velocity increases. However, a more realistic study considering filled minerals demonstrates decreasing shear wave velocity and counterintuitively rising compressional wave velocity when the porosity increases. Gas saturation only affects the compressional wave velocity. The obtained results improve our understanding of rock elastic behaviors in the coalbed. Cited as : Andhumoudine, A. B., Nie, X., Zhou, Q., Yu, J., Kane, O. I., Jin, L., Djaroun, R. R. Investigation of coal elastic properties based on digital core technology and finite element method. Advances in Geo-Energy Research, 2021, 5(1): 53-63, doi: 10.46690/ager.2021.01.06

Study on the Pore and Fracture Connectivity Characteristics of Oil Shale Pyrolyzed by Superheated Steam

The connectivity of the internal pores and fractures in oil shale is the critical factor in determining the success of the insitu pyrolysis of the oil shale with superheated steam. In this paper, using a self-developed superheated steam pyrolysis experimental system, oil shale samples were subjected to pyrolysis experiments at different steam temperatures. Then, the oil shale samples were scanned with high-precision micro-CT equipment to obtain the three-dimensional digital core of oil shale (DCOS). Based on the three-dimensional site percolation theory and renormalization group algorithm, the pore and fracture connectivity characteristics of the DCOSs were studied. The results show that when the steam temperature reached the pyrolysis temperature for oil shale, a series of pores was formed during the pyrolysis process. These pores gradually connected the adjacent fracture and subsequently formed a massive pore-fracture cluster. However, from room temperature to 555 °C, there were always parts with porosity less than 5% in the DCOSs perpendicular to the direction of the sedimentary bedding, forming the bottleneck of the seepage passage. This occurrence is the main reason that the permeability of the oil shale perpendicular to the direction of the sedimentary bedding is far lower than that parallel to the direction of the sedimentary bedding.

Study on Extraction Methods for Different Components in a Carbonate Digital Core

It is difficult to carry out petrophysical experiments because of the serious damage caused to cores in the development of fractures and pores in carbonate reservoirs. The development of a three-dimensional digital core in carbonate reservoirs has become a hot topic in rock physics research. Compared with the three-dimensional digital core, including basic rock skeletons and pores in sandstone reservoirs, carbonate reservoirs also include secondary structures such as microfractures. The carbonate contains different components, and extracting these components is a very difficult problem. The resolution on the electrical image log image is high, which can clearly reflect the macrocomponents in various reservoirs. There are some blank areas between electrodes on the electrical image log, which affects the extraction of components in a three-dimensional digital core. Aiming at the serious heterogeneities in the carbonate reservoirs and affecting image inpainting on the electrical image log image, a new method of image inpainting based on a combination of multipoint geostatistics and an interpolation method is put forward. The experimental results show that this method generates faster and better full-bore images than other methods. Due to the multipeak histogram, the maximum interclass variance in the two times method is proposed to extract macrocomponents such as basic rock skeletons, pores, and connected parts. The microfractures can be extracted from the CT scanned images by using image segmentation from the combination of the watershed and OTSU methods. The experimental results prove that using extraction methods for different components enables better results to be obtained.

Study on the C0–Cw relationship of clay-bearing sandstones based on digital cores

Based on the three-dimensional digital core of Berea sandstone, three-phase (matrix, wet clay and free water) digital cores of clay-bearing sandstone are constructed. We divide clay into structural clay and dispersed clay according to the location where clay growth occurs. The finite-element method is used to simulate the electrical characteristics of digital cores in order to study the relationship between the conductivity of core saturated with brine (C0) and the brine conductivity (Cw). The influence of clay mineral type, content and porosity on core electrical characteristics is taken into account. The results show that the additional conductivity is related to the clay minerals, and montmorillonite has the highest cation exchange capacity, resulting in the largest additional conductivity. The increase in clay content in cores increases the conductivity of core C0. At the same time, clay that fills pores decreases the porosity and causes the decrease in C0. These are two opposing factors of conductivity that coexist in clay-bearing sandstone.

Response laws of rock electrical property and saturation evaluation method of tight sandstone

To solve the problem that the law of rock electrical response under low and medium water saturation in tight sandstone reservoirs is not clear, an experimental method of high-speed centrifugal displacement rock electricity and nuclear magnetic resonance T2 spectrometry under different water saturation was proposed, which can drive the tight sandstone cores with the permeability less than 0.1×10−3 μm2, and provide a reliable experimental means for the study of tight sandstone electrical property. By carrying out supporting experiments such as high-resolution CT scan, MAPS and Qemscan, a multi-mineral component fine three-dimensional digital core based on multi-source information fusion was constructed. The finite element numerical simulation method was used to obtain the electrical response of tight sandstone core with low water saturation which cannot be obtained in laboratory conditions. By combining experiment and numerical simulation, the electrical response laws have been clear of tight sandstone with complex pore structure, and the saturation evaluation method of variable rock electrical parameters based on pore structure has been developed. The processing of logging data of multiple wells in tight sandstone reservoir of Chang 7 Member in the Ordos Basin shows that this method can obtain more accurate oil saturation, and provides a new idea and method for fine logging evaluation of tight sandstone reservoir.

Detailed characterization of micronano pore structure of tight sandstone reservoir space in three dimensional space: a case study of the Gao 3 and Gao 4 members of Gaotaizi reservoir in the Qijia area of the Songliao basin

Tight sandstone samples from the Gao 3 and Gao 4 members of Gaotaizi reservoir in Qijia area of the northern Songliao Basin were targeted as the main research objects in this paper. Through micro/nano CT technology and auto skeleton module and connectivity module in avizo software, three-dimensional models for the micro pore structure of Gaotaizi tight sandstone in the research area were constructed. The experimental results demonstrate that types of reservoir space include intergranular dissolution pores, intragranular dissolution pores, and micro-fractures, indicating remarkable microscopic heterogeneity with characteristics of a continuous distribution in a micronano scale. Under the micro scale, different physical property and sedimentary microfacies of tight reservoir show various pore structure characteristics in three-dimensional space, with the primary front of pore throats mainly distributed in 0.6~1.5 μm. Under the nanoscale, micro heterogeneity is remarkable, with the primary front of pore throats distributed in 40~100 nm. In addition, the nanopore distribution pattern in three-dimensional space mainly includes the nanopores in the granules and the nanofractures, of which the latter type plays a crucial role in connecting nanopores and migration of nano oil and gas migration; at the same time, this paper verify the digital core experimental results by using MICP technology. With the further development of big data technology and deep learning technology, three-dimensional digital core technology based on micro/nano CT technology will become an important technology applied in the exploration and development of unconventional oil and gas.

The Influence of Micro-Fractures on the Flow in Tight Oil Reservoirs Based on Pore-Network Models

In this paper, the influence of micro-fractures on the flow of tight reservoirs is studied on the microscopic scale. Three-dimensional digital cores of fractured tight sandstone with varying fracture apertures, lengths, and dip angles are constructed using computed tomography (CT) scans. Pore-network models are built using the three-dimensional digital cores to simulate the flow in tight oil reservoirs. The effects of the micro-fracture aperture, length and dip angle on the pore-throat structure, single-phase flow, and two-phase flow for fracture surfaces with/without roughness are studied. The study demonstrates different influences of micro-fracture characteristics on the flow, and the fracture aperture has the most critical effect. Meanwhile, the roughness of the micro-fracture makes a difference in addition to the three factors of micro-fractures. This paper provides a theoretical basis for the effective development of tight sandstone reservoirs.

Fractal dimension, lacunarity and succolarity analyses on CT images of reservoir rocks for permeability prediction

An explicit relationship between seepage properties and microscopic structure of porous media is being sought for the development of oil and gas resources. An effective method to accurately characterize and quantify the microscopic structure of porous media is a key issue. Fractal geometry can take advantage of several physically-based parameters to analyze microstructures of reservoir rocks. In this study, three fractal structural parameters, fractal dimension, lacunarity and succolarity, were employed to characterize scale-invariant complexity, heterogeneity, and anisotropy of rock microstructures, respectively. Twelve three-dimensional digital cores of sandstone reservoir rocks were used to evaluate permeability in terms of fractal dimension, lacunarity and succolarity. The parameters were utilized to quantitatively characterize differences in core micro-structure and predict their effects on permeability. Due to the confounding influence of porosity, the fractal dimension was not an accurate predictor of the variation in permeability on its own. Instead, the results reveal that lacunarity and succolarity were better able to predict differences in structure and permeability. Succolarity, in particular, showed an exponential relationship with permeability, yielding a coefficient of determination of 0.940. Using a combination of fractal structural parameters in the place of pore-size distribution, can provide a better explanation of the relationship between fluid flow, and the heterogeneous structure and anisotropic physical properties of reservoir rocks.

Influence mechanism of pore-scale anisotropy and pore distribution heterogeneity on permeability of porous media

Abstract Based on micro-CT scanning experiments, three-dimensional digital cores of tight sandstones were established to quantitatively evaluate pore-scale anisotropy and pore-distribution heterogeneity. The quartet structure generation set method was used to generate three-dimensional anisotropic, heterogeneous porous media models. A multi-relaxation-time lattice Boltzmann model was applied to analyze relationships of permeability with pore-scale anisotropy and pore distribution heterogeneity, and the microscopic influence mechanism was also investigated. The tight sandstones are of complex pore morphology, strong anisotropy and pore distribution heterogeneity, while anisotropy factor has obvious directivity. The obvious anisotropy influences the orientation of long axis of pores and fluid flow path, making tortuosity smaller and flowing energy loss less in the direction with the greater anisotropy factor. The strong correlation of tortuosity and anisotropy is the inherent reason of anisotropy acting on permeability. The influence of pore distribution heterogeneity on permeability is the combined effects of specific surface area and tortuosity, while the product of specific surface area and tortuosity shows significantly negative correlation with heterogeneity. The stronger the pore distribution heterogeneity, the smaller the product and the greater the permeability. In addition, the permeability and tortuosity of complex porous media satisfy a power relation with a high fitting precision, which can be applied for approximate estimation of core permeability.

Challenges and Prospects of Digital Core-Reconstruction Research

The simulation of various rock properties based on three-dimensional digital cores plays an increasingly important role in oil and gas exploration and development. The accuracy of 3D digital core reconstruction is important for determining rock properties. In this paper, existing 3D digital core-reconstruction methods are divided into two categories: 3D digital cores based on physical experiments and 3D digital core stochastic reconstructions based on two-dimensional (2D) slices. Additionally, 2D slice-based digital core stochastic reconstruction techniques are classified into four types: a stochastic reconstruction method based on 2D slice mathematical-feature statistical constraints, a stochastic reconstruction method based on statistical constraints that are related to 2D slice morphological characteristics, a physics process-based stochastic reconstruction method, and a hybrid stochastic reconstruction method. The progress related to these various stochastic reconstruction methods, the characteristics of constructed 3D digital cores, and the potential of these methods are analysed and discussed in detail. Finally, reasonable prospects are presented based on the current state of this research area. Currently, studies on digital core reconstruction, especially for the 3D digital core stochastic reconstruction method based on 2D slices, are still very rough, and much room for improvement remains. In particular, we emphasize the importance of evaluating functions, multiscale 3D digital cores, multicomponent 3D digital cores, and disciplinary intersection methods in the 3D construction of digital cores. These four directions should provide focus, alongside challenges, for this research area in the future. This review provides important insights into 3D digital core reconstruction.