Pore structure characteristics of reservoirs of Xihu Sag in East China Sea Shelf Basin based on dual resolution X-ray computed tomography and their influence on permeability

Zeng, Fang; Dong, Changyin; Chen, Lin; Tian, Shansi; Wu, Yuqi; Jiang, Lin; Liu, Binbin; Zhang, Xianguo

doi:10.1016/j.energy.2021.122386

Cited by 30 publications

(6 citation statements)

References 71 publications

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“…Shale oil exists mainly in free and adsorbed states, but adsorbed oil may be unrecoverable compared with free oil (bulk oil in the pores or fractures) − because of the nanoscale complex pore-fracture system. − Therefore, free oil mainly consisting of light hydrocarbon components, rather than adsorbed oil, is the main development target under current technological conditions . Moreover, the recoverable part of the free oil is called movable oil, which has the best flowability .…”

Section: Introductionmentioning

confidence: 99%

Key Oil Content Parameter Correction of Shale Oil Resources: A Case Study of the Paleogene Funing Formation, Subei Basin, China

Zhang

Lin

et al. 2022

Energy Fuels

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Estimating shale oil resources is critical in shale oil exploration, and the pyrolysis parameter S 1 is a frequently used parameter to assess the oil amount in shale. However, S 1 loses some light and heavy hydrocarbons due to core storage conditions and experimental technology, resulting in underestimating shale oil resources. In this paper, a set of models were developed to correct the light and heavy hydrocarbon losses for S 1 based on conventional and multistage Rock-Eval experiments on liquefrozen and room-temperature shales collected from the Funing Formation, Subei Basin. Two types of correction models of heavy hydrocarbon loss for liquefrozen and room-temperature shales were determined by comparing the conventional and multistage Rock-Eval experiments, respectively. The light hydrocarbon loss correction model was obtained according to conventional Rock-Eval experiments on liquefrozen and room-temperature shales. Moreover, the estimation models of adsorbed, free, and movable amounts of oil were determined and validated by the oil saturation index (OSI) method. The results show that the total, adsorbed, free, and movable oil contents can be estimated well by these correction models. A case study from the Funing Formation, Subei Basin, indicates that the higher the content of total oil, the higher the amounts of free and movable oil, indicating that shale with more oil also has a more excellent mobile and developable potential. Organic matter is the main adsorbent for shale oil. Shales with TOC greater than 1.5% generally have greater free (movable) oil amounts, which may be the optimal target for shale oil exploration and exploitation. This study provides an innovative approach to correct the key parameters of shale oil resources, and thus, is crucial for the exploration and development of shale oil in the Funing Formation, Subei Basin.

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Section: Introductionmentioning

confidence: 99%

Key Oil Content Parameter Correction of Shale Oil Resources: A Case Study of the Paleogene Funing Formation, Subei Basin, China

Zhang

Lin

et al. 2022

Energy Fuels

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“…Pore-scale fluid flow experiment is an effective method to investigate the transport mechanisms and distribution characteristics of residual oil, including microfluidics [5][6][7][8], natural sandstone models [9][10][11][12][13], nuclear magnetic resonance [14][15][16], confocal laser [17][18][19], and CT scan [20][21][22]. Owing to the rapid development of CT technology, it has been widely used in EOR [23][24][25][26][27], carbon dioxide storage [28], environmental governance [29], water-rock interaction [30,31], reservoir modelling [32][33][34][35][36], hydraulic conductivity [37,38], and reservoir evaluation [39][40][41][42][43][44][45][46][47]. Due to the advantages of high resolution, nondestructive, and in situ, CT scan has become an effective method for investigating residual oil.…”

Section: Introductionmentioning

confidence: 99%

Effects of Wettability and Minerals on Residual Oil Distributions Based on Digital Rock and Machine Learning

Zhang

Lin

et al. 2022

Lithosphere

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The wettability of mineral surfaces has significant impacts on transport mechanisms of two-phase flow, distribution characteristics of fluids, and the formation mechanisms of residual oil during water flooding. However, few studies have investigated such effects of mineral type and its surface wettability on rock properties in the literature. To unravel the dependence of hydrodynamics on wettability and minerals distribution, we designed a new experimental procedure that combined the multiphase flow experiments with a CT scan and QEMSCAN to obtain 3D digital models with multiple minerals and fluids. With the aid of QEMSCAN, six mineral components and two fluids in sandstones were segmented from the CT data based on the histogram threshold and watershed methods. Then, a mineral surface analysis algorithm was proposed to extract the mineral surface and classify its mineral categories. The in situ contact angle and pore occupancy were calculated to reveal the wettability variation of mineral surface and distribution characteristics of fluids. According to the shape features of the oil phase, the self-organizing map (SOM) method, one of the machine learning methods, was used to classify the residual oil into five types, namely, network, cluster, film, isolated, and droplet oil. The results indicate that each mineral’s contribution to the mineral surface is not proportional to its relative content. Feldspar, quartz, and clay are the main minerals in the studied sandstones and play a controlling role in the wettability variation. Different wettability samples show various characteristics of pore occupancy. The water flooding front of the weakly water-wet to intermediate-wet sample is uniform, and oil is effectively displaced in all pores with a long oil production period. The water-wet sample demonstrates severe fingering, with a high pore occupancy change rate in large pores and a short oil production period. The residual oil patterns gradually evolve from networks to clusters, isolated, and films due to the effects of snap-off and wettability inversion. This paper reveals the effects of wettability of mineral surface on the distribution characteristics and formation mechanisms of residual oil, which offers us an in-deep understanding of the impacts of wettability and minerals on multiphase flow and helps us make good schemes to improve oil recovery.

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“…In recent years, a series of technologies, including highpressure mercury injection, low-temperature nitrogen and carbon dioxide adsorption, field emission scanning electron microscope, atomic force microscope, nuclear magnetic resonance, small-angle neutron scattering, and high-resolution CT scanning, improved the measurement accuracy of pore size from micron to nanoscale. Moreover, the comprehensive use of various methods increases the characterization accuracy of unconventional reservoirs (Wu et al, 2019a;Wu et al, 2019b;Wu et al, 2019c;Wu et al, 2020b;Wu et al, 2020c;Wu et al, 2020d;Zeng et al, 2022). At the same time, considering the high complexity of shale and tight sandstone samples, Euclidean geometry cannot give accurate description and characterization.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Control of Pore Structural Heterogeneity for Low-Thermal-Maturity Shale: A Case Study of the Shanxi Formation in the Northeast Zhoukou Depression, Southern North China Basin

Liu

Shi

et al. 2022

Front. Earth Sci.

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The Shanxi Formation layers in the northeast of the Zhoukou Depression, Southern North China Basin, mainly consist of dark mudstone interbed with tight stone and widely developed coal seam, which is a promising target for unconventional oil and gas exploration. A series of geochemical and geological methods were used to analyze the characterization and controls of the pores structural heterogeneity in low-thermal-maturity shale. These methods include the Rock-Eval analysis, total organic carbon (TOC) analysis, scanning electron microscope observation with an energy-dispersive spectrometer (SEM-EDS), X-ray diffraction, and low-pressure N2 adsorption. Based on these measurements, the pore diameter, specific surface area (SSA), and fractal dimension (D) were calculated, and then, the pore structure heterogeneity was analyzed. The result shows the pores of Shanxi Formation shale are mainly interparticle pores with low porosity and low permeability, and the pore structure is highly complex. The average fractal dimension of the micropore and the macropore are both 2.77, but that of the mesopore is 2.65, indicating a less-complex mesopore structure than the micropore and macropore. The S2, S1, and TOC exhibit no clear correlation with SSA and fractal dimension of pores, which proved the little impact of organic matter on the heterogeneity of pore structure in the low-maturity shale of the research area. The illite has a strong effect on the pore structural heterogeneity of Shanxi Formation shale. The samples with high content of illite show higher SSA, better physical properties, and low fractal dimension, reflecting low pore structural heterogeneity. However, the quartz and clay minerals show a slight correlation with SSA and no obvious relationship with the fractal dimension, indicating a little effect of them on the pore structure heterogeneity. The pore structural heterogeneity decreases along with the increase in porosity, while the permeability influenced by a variety of reasons under the compaction shows a poor relationship with SSA and fractal dimension. On the whole, the pore structural heterogeneity decreases for low-thermal-maturity shale with high content of illite and high porosity, which should be considered to be the better unconventional oil and gas reservoir in the research area.

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Pore structure characteristics of reservoirs of Xihu Sag in East China Sea Shelf Basin based on dual resolution X-ray computed tomography and their influence on permeability

Cited by 30 publications

References 71 publications

Key Oil Content Parameter Correction of Shale Oil Resources: A Case Study of the Paleogene Funing Formation, Subei Basin, China

Key Oil Content Parameter Correction of Shale Oil Resources: A Case Study of the Paleogene Funing Formation, Subei Basin, China

Effects of Wettability and Minerals on Residual Oil Distributions Based on Digital Rock and Machine Learning

Characterization and Control of Pore Structural Heterogeneity for Low-Thermal-Maturity Shale: A Case Study of the Shanxi Formation in the Northeast Zhoukou Depression, Southern North China Basin

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