Pore structure and its control on reservoir quality in tight sandstones: a case study of the Chang 6 member of the Upper
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ORIGINAL PAPER-EXPLORATION GEOLOGY
Pore structure and its control on reservoir quality in tight sandstones: a case study of the Chang 6 member of the Upper Triassic Yanchang Formation in the Jingbian oilfield in the Ordos Basin, China Yubin Bai1,2 · Jingzhou Zhao1,2 · Delin Zhao1 · Hai Zhang3 · Yong Fu4 Received: 9 January 2020 / Accepted: 6 November 2020 © The Author(s) 2020
Abstract This study applied vacuum-impregnated casting thin sections, fluorescence slices, scanning electron microscopy (SEM), pressure-controlled mercury porosimetry (PCP), rate-controlled mercury porosimetry (RCP), X-ray diffraction of clay minerals, overburden pressure, and conventional physical property strategies to determine the microscopic characteristics of the Chang 6 member, a typical tight sandstone reservoir in the Jingbian oilfield in the Ordos Basin, China. We also analyzed the controlling effects of pore structure on reservoir quality and oiliness. The results showed that the pore types of the Chang 6 sandstone reservoir can be divided into four categories: residual intergranular pores, dissolution pores, intercrystalline pores between clay minerals, and microfractures. The pore size of the Chang 6 sandstone reservoir ranged from 20 to 50 μm. We employed PCP and RCP strategies to characterize the pore structure of the Chang 6 reservoir. The pore radius was less than 2 μm, and on average, the throat radius was less than 0.3 μm. The reservoir physical properties were affected by diagenesis, particularly compaction, and the average porosity failure rate was 56.3%. Cementation made the reservoir more compact, dissolution improved the physical properties of the reservoir locally, and fracturing effectively improved the reservoir seepage ability; however, its influence on porosity was limited. The pore structure controlled the quality of the reservoir. The physical properties of the reservoir were closely related to the oil-bearing properties. The lower limits of porosity and permeability of industrial oil flow in the reservoir were 7.5% and 0.15 mD, respectively. These results provide an additional resource for the exploration and development of tight oil in the Ordos Basin. Keywords Tight sandstone · Pore structure · Chang 6 member · Jingbian oilfield · Ordos basin
Introduction Given the increasing difficulty of conventional oil and gas exploration and development, unconventional oil and gas resources are attracting global attention (Rogner 1997; Zou et al. 2012; Holditch 2013; Zhao et al. 2013; Islam 2014; * Yubin Bai [email protected] 1
School of Earth Sciences and Engineering, Xi’an Shiyou University, Xi’an 710065, Shaanxi, China
2
Shaanxi Key Lab of Petroleum Accumulation Geology, Xi’an Shiyou University, Xi’an, Shaanxi, China
3
Jingbian Oil Production, Yanchang Oilfield Corporation, Yulin, Shaanxi, China
4
College of Geosciences, China University of Petroleum (Beijing), Beijing, China
Al-Fatlawi et al. 2019). Developing unconventional oil and gas is an inevitable trend in industry; in fact, from the p
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