Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5483913 | Journal of Petroleum Science and Engineering | 2017 | 16 Pages |
Abstract
The Xiagou Formation is the main tight oil reservoir in the Qingxi Depression of the Jiuquan Basin; however, its poor physical properties have restricted tight oil exploration and development. Therefore, itis important to gain a better understanding of its micropore structure. The results show that the lithology of the Xiagou Formation reservoir is dominated by gray argillaceous dolomite and dolomitic mudstone. The pore types are primarily composed of elliptical and irregular intergranular pores. Intercrystalline and organic-matter-hosted pores are mostly isolated and have poor connectivity. Moreover, NMR spectroscopy results show that the T2spectra of the rock samples in the study area are predominantly unimodal or bimodal in distribution, with pore sizes principally ranging between 0.01 and 0.69 μm. Using CT scanning, we obtained a three-dimensional (3D) pore-throat stereogram. At the micrometer scale, the pore throats differed in size and exhibited shelf-like, banded, and spheroidal shapes. At the nanometer scale, we observed a greater number of nanometer-scale micropores. These pores were shelf-like and spheroidal in shape and were distributed inside or at the mineral grain (crystal) surface. The nanometer-scale spheroidal micropores showed poor connectivity and were isolated in 3D space, with most serving as reservoir spaces. However, the nanometer-scale short-shelf-like micropores showed connectivity with the micrograde shelf-like micropores, were adjacent to the isolated spheroidal nanometer-scale micropores, and acted as both pore throats and pores. The larger throat-to-pore ratio coefficient indicates a greater correlation between the pore and throat, which further results in a higher concentration of pores. The larger average pore volume leads to higher porosity and, together with the higher average coordination number, enables better pore connectivity, thereby yielding a better potential reservoir and penetration capacity.
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Authors
Qun Luo, Chen Zhang, Quanqi Dai, Dongdong Liu, Wei Yang, Luofu Liu, Xiangye Kong, Xinpeng Wang, Xiaoyu Liu, Keji Yang,