Pore characteristic responses to categories of depositional microfacies of delta-lacustrine tight reservoirs in the Upper Triassic Yanchang Formation, Ordos Basin, NW China

Yang, Wei; Wang, Qianyou; Wang, Yaohua; Jiang, Zhenxue; Song, Yan; Li, Yaohua; Liú, Dan; Zuo, Rusi; Gu, Xiaomin; Zhang, Fan

doi:10.1016/j.marpetgeo.2020.104423

Cited by 38 publications

(12 citation statements)

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“…Xiuwu shale is expected to have the highest maturity among marine shales. A shale sample from Ordos Basin is an example of a marine-continental transitional shale deposit in Carboniferous [75][76][77].…”

Section: Samples and Experimental Methodsmentioning

confidence: 99%

Petrographic Characterization and Maceral Controls on Porosity in Overmature Marine Shales: Examples from Ordovician-Silurian Shales in China and the U.S.

et al. 2021

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The pore structure characterization and its controlling factors in overmature shales are keys to understand the shale gas accumulation mechanism. Organic matter in source rocks is a mixture of various macerals that have their own specific evolutionary pathways during thermal maturation. Pores within macerals also evolve following their own path. This study focused on petrographic characterization and maceral controls on porosity in overmature marine shales in China and the United States. Shale from Ordos Basin in China was also selected as an example of overmature transitional shale for maceral comparison. Organic petrology techniques were used to identify maceral types and describe morphological features in detail; scanning electron microscopy techniques were then used to document the abundance and development of pores within macerals. Helium measurement, mercury intrusion capillary pressure, and CO2 adsorption were especially applied to quantify the pore structure of Wufeng-Longmaxi shale from Sichuan Basin in China. The vitrinite reflectance equivalent of the studied overmature samples is ~2.4%. The macerals within the studied marine shales are composed mainly of pyrobitumen and zooclasts. At this maturity, pyrobitumen develops abundant gas-related pores, and their volume positively correlates to gas content. Three types of pyrobitumen and its related pore structure are characterized in Wufeng-Longmaxi shales. Zooclasts contribute to total organic carbon (TOC) content but little to porosity. When the TOC content is above 1.51% in Wufeng-Longmaxi samples, the TOC content positively correlates to quartz content. Organic matter strongly controls micropore development. Pores of diameter ~ 0.5 nm provide a significant amount of micropore volume. Clay mineral and quartz contents control micro- and macropore increments in organic-lean shales. MICP results indicate that pores within 3-12 nm and 900-2500 nm account for a major contribution to pore volume obtained. Determining the proportions of pyrobitumen to zooclasts within the total organic matter in pre-Devonian organic-rich marine shales is important in predicting porosity and gas storage capacity in high-maturity shales.

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Section: Samples and Experimental Methodsmentioning

confidence: 99%

Petrographic Characterization and Maceral Controls on Porosity in Overmature Marine Shales: Examples from Ordovician-Silurian Shales in China and the U.S.

et al. 2021

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“…Dolomite and mudstone developed widely with a long and consistent hydrocarbon charging history, yielding abundant oil and gas, whereas numerous tight oil reservoirs have occurred around oil and gas reservoirs in the area [17][18][19]. With the continuous exploration of tight reservoirs in Liugouzhuang, Qingxi Sag, Jiuquan Basin, massive geological data and useful practice experiences are accumulated; however, difficulty arises from analyzing the pore structure of the tight oil reservoir in the Xiagou Formation, and the accuracy of pore structure classification and evaluation remains low [20][21][22][23][24][25]. Therefore, this work is aimed at investigating the pore structure characteristics of the Xiagou Formation in Qingxi Sag, Jiuquan Basin, to discuss the comprehensive division and assessment methods of the pore structure in tight oil carbonate reservoirs, improving classification accuracy of "sweet spots" in the reservoir, and to provide guidance for the exploration and development of tight oil carbonate reservoirs.…”

Section: Introductionmentioning

confidence: 99%

Pore Structure Characteristics of Tight Carbonate Reservoir in Qingxi Sag, Jiuquan Basin

et al. 2021

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The Xiagou Formation is the main tight oil reservoir in Qingxi Sag of Jiuquan Basin. Given the poor physical properties and other factors restricting tight oil exploitation and production in this area, studies should focus on microscopic pore structure characteristics. In this study, a nano-CT scanner, a SEM, and an NMR were used to study the pore structure characteristics of a tight carbonate reservoir in Qingxi Sag, Jiuquan Basin. The Xiagou Formation reservoir mainly consists of gray argillaceous dolomite and dolomitic mudstone. The pore categories are mainly elliptic, irregular, intergranular, and intragranular and mostly filled with clay and carbonate cement. Pore space is small, the intergranular or organic pores are mostly separated, and pore-throat is weakly connected. The throats mostly develop with lamellar and tube bundle-like characteristics and with poor seepage ability. The pore-throats mostly span from nanometer to micrometer sizes, and pore diameters are mainly concentrated in the range of 0.01–0.1 and 1–10 μm. It is a unimodal pattern mainly composed of micropores, or a bimodal regular allocation dominated by micropores supplemented by macropores. The relationship between micropore (<0.1 μm) and macropore (>1 μm) content allocation and mean pore diameter strongly controls the permeability of reservoir rocks. When macropore content reaches more than 85%, or when pore content totals less than 3%, the permeability of a reservoir remarkably increases. At a higher ratio of the average finest throat sectional area and throat-pore of reservoir rock, the throat radius lies closer to the connecting pore radius, pore and throat connectivity improves, and reservoir seepage ability becomes stronger. Based on reservoir capacity and seepage ability, pore structures of the tight carbonate reservoirs in study area are classified into type I (small-pore–thin-throat), type II (thin-pore–thin-throat), and type III (microporous-microthroat) with rock permeability>0.1 mD, 0.05–0.1 mD, and <0.05 mD, respectively. The type I pore structure reservoir should be regarded as an indicator of tight oil “sweet spots” reservoir in the study area.

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confidence: 87%

“…The greater the inter-layer permeability difference is, the lower the oil displacement efficiency is. These research results highlight the characteristics and micro-seepage of reservoir, however, there are few studies on the law of water-flooding in the whole reservoir, and there are few reports on the analysis of water-flooding characteristics based on reservoir production performance data [10][11][12] .At present, the water-flooding efficiency of Chang 4 + 5 reservoir in Jiyuan area of Ordos Basin is low, and the research on reservoir characteristics, water flooding characteristics and influencing factors is relatively poor. In this paper, taking Chang 4 + 5 in Jiyuan oilfield as an example, representative core samples are selected, and the microscopic characteristics of reservoir are discussed by physical properties, constant-speed mercury injection, scanning electron microscope and thin section observation, and production performance data.…”

mentioning

confidence: 89%

Water-flooding characteristics of lithologic reservoir in Ordos basin

Liu

Zhu

et al. 2021

Sci Rep

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Due to the poor situation of water-flooding mechanism research on Chang 4 + 5 reservoir of Ordos basin, the authors quantitatively studied the influence factors of water-flooding characteristics by sedimentology, casting thin sections, constant-speed mercury injection, scanning electron microscope as well as production records. The size and distribution of pore-throat were also found closely related with the water-flooding seepage law. The results show that the microscopic seepage paths of Chang 4 + 5 reservoir include uniform displacement, finger displacement and peak displacement, and their correspondent oil displacement efficiency reduces in turn under the same conditions. Reservoir heterogeneity, reservoir properties, distribution of pore structure and wettability play a decisive role in water-flooding efficiency. Generally, When the intra-layer range is greater than 4.65, the breakthrough coefficient is greater than 3.54, the coefficient of variation is greater than 0.7, the distribution frequency of inter-layer is greater than 0.5 per meter, and the distribution density is greater than 0.435%, the range between layers is greater than 6.86, the breakthrough coefficient is greater than 2.58, the coefficient of variation is greater than 0.51, and the thickness of inter-layer is greater than 7.54 m. the increasing trend of oil displacement efficiency will be obviously weakened.

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Pore characteristic responses to categories of depositional microfacies of delta-lacustrine tight reservoirs in the Upper Triassic Yanchang Formation, Ordos Basin, NW China

Cited by 38 publications

References 115 publications

Petrographic Characterization and Maceral Controls on Porosity in Overmature Marine Shales: Examples from Ordovician-Silurian Shales in China and the U.S.

Petrographic Characterization and Maceral Controls on Porosity in Overmature Marine Shales: Examples from Ordovician-Silurian Shales in China and the U.S.

Pore Structure Characteristics of Tight Carbonate Reservoir in Qingxi Sag, Jiuquan Basin

Water-flooding characteristics of lithologic reservoir in Ordos basin

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