Genesis and microscopic characteristics of tight reservoirs in the Fengcheng Formation, at the southern margin of the Mahu Sag

被引:3
作者
Bai, Luning [1 ]
Huang, Wenbiao [1 ]
Qin, Jun [2 ]
Zhang, Zongbin [2 ]
Ba, Zhongchen [2 ]
Bai, Zhenhua [3 ]
Guo, Yibing [1 ]
Li, Heng [1 ]
机构
[1] China Univ Petr East China, Sch Geosci, Qingdao 266580, Shandong, Peoples R China
[2] PetroChina Xinjiang Oilfield Co, Res Inst Explorat & Dev, Karamay 834000, Xinjiang, Peoples R China
[3] PetroChina Daqing Oilfield Co, Res Inst Explorat & Dev, Daqing 163712, Heilongjiang, Peoples R China
来源
ENERGY GEOSCIENCE | 2023年 / 4卷 / 03期
关键词
Tight reservoir; Pore-throat structure; Reservoir classi fication; Diagenesis; Fengcheng Formation; Mahu Sag; NUCLEAR-MAGNETIC-RESONANCE; PORE-THROAT STRUCTURE; JUNGGAR BASIN; INJECTION; SLOPE; SHALE;
D O I
10.1016/j.engeos.2023.100162
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
The tight reservoirs of the Fengcheng Formation at the southern margin of the Mahu Sag have strong heterogeneity due to the diversity in their pore types, sizes, and structures. The microscopic characteristics of tight reservoirs and the mechanisms that generate them are of significance in identifying the distribution of high-quality reservoirs and in improving the prediction accuracy of sweet spots in tight oil reservoirs. In this paper, high-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR) experiments were carried out on samples from the tight reservoirs in the study area. These experimental results were combined with cluster analysis, fractal theory, and microscopic observations to qualitatively and quantitatively evaluate pore types, sizes, and structures. A classification scheme was established that divides the reservoir into four types, based on the microstructure characteristics of samples, and the genetic mechanisms that aided the development of reservoir microstructure were analyzed. The results show that the lower limit for the tight reservoir in the Fengcheng Formation is F of 3.5% and K of 0.03 mD. The pore throat size and distribution span gradually decrease from Type I, through Type II and Type III reservoirs to non-reservoirs, and the pore type also evolves from dominantly intergranular pores to intercrystalline pores. The structural trend shows a decrease in the ball-stick pore-throat system and an increase in the branch-like pore-throat system. The dual effects of sedimentation and diagenesis shape the microscopic characteristics of pores and throats. The sorting, roundness, and particle size of the original sediments determine the original physical properties of the reservoir. The diagenetic environment of 'two alkalinity stages and one acidity stage' influenced the evolution of pore type and size. Although the cementation of authigenic minerals in the early alkaline environment adversely affected reservoir properties, it also alleviated the damage of the later compaction to some extent. Dissolution in the mid-term acidic environment greatly improved the physical properties of this tight reservoir, making dissolution pores an important reservoir space. The late alkaline environment occurred after large-scale oil and gas accumulation. During this period, the cementation of authigenic minerals had a limited effect on the reservoir space occupied by crude oil. It had a more significant impact on the sand bodies not filled with oil, making them function as barriers. (c) 2023 Sinopec Petroleum Exploration and Production Research Institute. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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页数:12
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