Types and resource potential of continental shale oil in China and its boundary with tight oil

Zhao, Wenzhi; Hu, Suyun; Hou, Lianhua; Yang, Tao; Li, Xin; Guo, Bin; Yang, Zhi

doi:10.1016/s1876-3804(20)60001-5

Cited by 279 publications

(148 citation statements)

References 14 publications

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“…Permeability reflects the migration ability of reservoir, which is one of the important parameters to evaluate reservoir. The permeability of unconventional reservoirs is very low, and the permeability of shale oil reservoirs is generally a few millidarcy [19]. Shale is dense, and its permeability is mainly provided by internal microfractures.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Hydration Damage and Its Influence on Permeability of Lamellar Shale Oil Reservoirs in Ordos Basin

et al. 2021

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The continental shale oil reservoir has low permeability, high clay content, rich lamellar structure, and strong heterogeneity, which makes the reservoir vulnerable to hydration damage. In order to study characteristics of hydration damage and its influence on permeability of lamellar shale oil reservoirs, a series of experiments such as high-pressure mercury injection, steady gas permeability, rock thin section identification, and scanning electron microscope were carried out with the downhole core in Ordos Basin as the experimental object. The effects of water and water-based drilling fluid on pore size distribution, permeability, and rock microstructure were analyzed. Results show that the pore size of the reservoir is mainly nanoscale, and the pore size of shale changes most dramatically in the stage of hydration for 12-24 hours, while that of tuff changes most dramatically in 24-48 hours. The permeability increases rapidly with hydration time and then tends to be stable, among which the permeability of samples with lamellar structure in the direction parallel to the lamellar structure is most easily affected by hydration and changes fastest. Hydration leads to the formation of new pores, new fractures, and the expansion of existing fractures in rocks, especially in the strata containing large amounts of terrigenous clastic, lamellar structure, and pyrite. The new seepage channel increases the permeability of rock, and the soil powder and plugging particles in drilling fluid are easy to form protective mud cake in these places. These protective mud cakes not only change the microstructure of rock but also inhibit the influence of hydration on the pore space and permeability of rock, which play an effective role in preventing the mineral shedding on the rock surface, reducing the increase of micropores and delaying hydration.

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Section: Introductionmentioning

confidence: 99%

Characteristics of Hydration Damage and Its Influence on Permeability of Lamellar Shale Oil Reservoirs in Ordos Basin

et al. 2021

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“… 7 − 13 The Middle Permian Lucaogou Formation (P 2 l) in the Jimsar Sag of the Junggar Basin, NW China, is one of the main areas of lacustrine shale oil exploration and exploitation in China. 14 − 16 Oil production has shown that the Lucaogou Formation has upper and lower sweet spots, both characterized by marked heterogeneity and frequent interbedded shale and tight reservoirs. 17 , 18 The current exploration target is focused on the tight oil reservoirs of the formation 16 because whether oil in shale is also a potential exploration target remains uncertain.…”

Section: Introductionmentioning

confidence: 99%

“… 14 − 16 Oil production has shown that the Lucaogou Formation has upper and lower sweet spots, both characterized by marked heterogeneity and frequent interbedded shale and tight reservoirs. 17 , 18 The current exploration target is focused on the tight oil reservoirs of the formation 16 because whether oil in shale is also a potential exploration target remains uncertain. A method to determine whether the oil is produced from shale in the Lucaogou Formation needs to be clarified.…”

Section: Introductionmentioning

confidence: 99%

Identification of Oil Produced from Shale and Tight Reservoirs in the Permian Lucaogou Shale Sequence, Jimsar Sag, Junggar Basin, NW China

Hou

Zhao

et al. 2021

ACS Omega

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The Permian Lucaogou Formation of the Jimsar Sag in the Junggar Basin, NW China, is one of the largest areas of oil exploration and exploitation in the lacustrine shale sequence in China. Oil is commercially extracted from this markedly heterogeneous formation, which is characterized by frequently interbedded shale and tight reservoirs, although producible intervals within the Lucaogou Formation remain unresolved. This study focused on the Jimsar Sag reservoirs to investigate petrological and mineralogical characteristics, source rock and reservoir physical properties, and the molecular biogeochemistry of core extracts and crude oils. The i-C18/n-C18 and Pr/n-C19 ratios of two-step ultrasonic extracts were applied to infer whether the oil is produced from shale or tight reservoirs, taking into account solvent polarity, molecular characteristics of n-alkanes and isoprenoids, and physical properties of the reservoir. The experimental results indicated that the shallower pay zone is mainly produced from tight reservoirs, while in deeper zone with organic-matter maturity above 1.0%, some of the oil is produced from shale. The reservoir properties in organic-rich shale with vitrinite reflectance (Ro) exceeding 1.0% are improved by pore interconnectivity, and oil mobility is enhanced by high gas/oil ratios, which favors production of free-phase hydrocarbons. Such zones may become major prospects for shale oil exploration and production. The results of the present study can potentially apply to sweet-spot identification and development optimization for the Lucaogou shale and other lacustrine shale sequences.

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“…Unconventional tight oil and gas resources in China are widely distributed and have great development potential [2,3]. Tight oil and gas resources are found in the Triassic strata of the Ordos basin, Permian strata of the Junggar basin, Cretaceous strata of the Songliao basin, Paleogene strata of the Bohai-Bay basin, and other strata, which have broad prospects of exploration and development [4]. The tight oil in the Ordos basin is a typical representative of the tight oil resources of continental sedimentation in China.…”

Section: Introductionmentioning

confidence: 99%

“…It is obvious that the relaxation time T 2 is theoretically a linear function of pore radius r c . Therefore, the distribution 4 Geofluids of fluids in various pores can be calculated by measuring the signal of the hydrogen nucleus.…”

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confidence: 99%

Characterization of the Dynamic Imbibition Displacement Mechanism in Tight Sandstone Reservoirs Using the NMR Technique

et al. 2020

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An experimental technique is developed to investigate the dynamic imbibition displacement mechanism in tight sandstone formations of the Yanchang group of the Ordos basin. By combining the dynamic imbibition core flooding experiments and NMR technique, the effects of the injection volume and rate on displacement efficiency are investigated. Moreover, the displacement efficiency of dynamic imbibition is compared with that of static imbibition. This study gains insights into the micromechanisms of dynamic imbibition in tight sandstone formations. It is found that the relative displacement efficiency of dynamic imbibition increases with the increase of injection volume. But the increment amplitude decreases with the increase of injection volume. With the same injection volume, the core displacement efficiency of dynamic imbibition with high permeability is obviously improved. However, the core displacement efficiency decreases rapidly with the increase of injection volume. Optimal injection volumes are recommended for tight sandstone formations with different permeabilities. With the increase of the displacement rate, the core displacement efficiency of dynamic imbibition shows a trend of first rising and then declining. There exists an optimal displacement rate in dynamic imbibition displacement, and the optimal displacement rate almost linearly increases with the increase of core permeability. The static imbibition displacement efficiency increases with the increase of soaking time, but the increment amplitude slows down obviously. The displacement efficiency of static imbibition in small pores is higher than that of dynamic imbibition. The displacement efficiency of dynamic imbibition in large pores or microcracks is significantly higher than that of static imbibition. This study provides theoretical support for the optimization and improvement of the waterflooding recovery process in tight sandstone reservoirs.

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Types and resource potential of continental shale oil in China and its boundary with tight oil

Cited by 279 publications

References 14 publications

Characteristics of Hydration Damage and Its Influence on Permeability of Lamellar Shale Oil Reservoirs in Ordos Basin

Characteristics of Hydration Damage and Its Influence on Permeability of Lamellar Shale Oil Reservoirs in Ordos Basin

Identification of Oil Produced from Shale and Tight Reservoirs in the Permian Lucaogou Shale Sequence, Jimsar Sag, Junggar Basin, NW China

Characterization of the Dynamic Imbibition Displacement Mechanism in Tight Sandstone Reservoirs Using the NMR Technique

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