Microscale Mineral and Pore Structure Characterization of the Low-Permeability Sandstone in the Ordos Basin, China

Jie Gao,Dazhong Ren,Dengke Liu,Rongjun Zhang,Chenyang Zhao,Jianping Liu,Tingting Li,Zhen Sun,Xiaohu Zhang

doi:10.1155/2021/6448271

Abstract

Given the insufficient understanding of the characteristics and controlling factors of the low-permeability sandstone reservoir in the Heshui area, the Ordos Basin, the present study examined the microscale mineral and pore structure of Chang 2 reservoir. It analyzed its major controlling factors using a series of methods, including imaging and indirect methods. The results show that the rocks of Chang 2 reservoir in the study area are dominated by lithic arkose and feldspathic detritus quartz sandstone. The reservoir space develops intragranular pores, feldspar dissolved pores, lithic dissolved pores, and intercrystallite pores. Microcracks can occasionally be found. The average porosity is 10.5%, and the average permeability is 2.2 mD, featuring a low-porosity-ultralow-permeability reservoir. During the reservoir development, traps formed by small-scale nose-shaped uplifts resulting from the tectonic effects provide opportunities for good reservoir space. Sedimentation and diagenetic processes control the degree of development and direction of the evolution of reservoir porosity to a certain degree. Multisegment capillary pressure curve and long missing zone were corresponding to relatively good pore-throat structures. Illite was the predominant diagenetic clay minerals that determine the reservoir quality. These three effects all contribute to the overall development of the reservoir.

Highlights

Jie Gao,1 Zhen Sun,2 Jianping Liu,3 Chenyang Zhao,3 Dazhong Ren,4 Rongjun Zhang,4 Tingting Li,1 and Dengke Liu 5
Given the insufficient understanding of the characteristics and controlling factors of the low-permeability sandstone reservoir in the Heshui area, the Ordos Basin, the present study examined the microscale mineral and pore structure of Chang 2 reservoir
Through the exploration and evaluation of the Heshui area, scholars have found that the yield of Chang 2 reservoir in oil tests was relatively high. is finding is vital for increasing China’s oil production and reserve, demonstrating the vast potential for future prospection and development [4, 5]

Summary

Methodology

E general structure of the Heshui area features a gentile monocline oriented on an east-west axis, without any faults or large-scale basement uplifts. The structures above in the study area affect the distribution of oil pools, their influence is only marginal. The samples were first polished as a cube, milled via argon ion. After those steps, the samples were coated with carbon. The samples were put into the apparatus and the relationship between capillary pressure and mercury saturation was tested. E pre-exam procedures were the same as that of PCMI In this test, the maximum pressure was not over 6.2 MPa, corresponding to the pore radius of 0.12 μm

Results and Discussion

VII VIII

Conclusions