Investigation of Rock Properties Governing Gas Storage Capacity in Nanoporous Shales
Restricted (Penn State Only)
- Author:
- Lou, Xuanqing
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 10, 2023
- Committee Members:
- Jeremy Gernand, Program Head/Chair
Zuleima Karpyn, Chair & Dissertation Advisor
Shimin Liu, Major Field Member
Luis Ayala H, Major Field Member
Elizabeth Hajek, Outside Unit & Field Member - Keywords:
- Unconventional reservoirs
shale gas
storage capacity
X-ray CT
Digital rock analysis - Abstract:
- Shale gas has become a major source of energy in today’s world, and the exploitation of shale gas reservoirs has led to an increase in natural gas production in recent years. A unique characteristic of shales, which has made their development challenging, is the coexistence of complex composition and the abundance of nano-scale pores. These shale properties make gas storage behavior in shales fundamentally different from that in conventional reservoir rocks. This study focuses on the investigation of shale pore structural and compositional properties, and to assess their relative contribution on gas storage capacity. A methodology using nano-CT imaging as a main tool is presented to characterize the pore structure of natural nanoporous materials with a wide range of pore size (nano- to micrometer-scale). This methodology offers both the characterization of the shale rock pore size distribution and specific surface area and inputs for pore-scale fluid simulations. To quantify gas storage capacity in the form of density, a robust methodology based on the principles of X-ray physics is proposed, which allows one to directly measure in-situ fluid density within shale rocks. The results show good accuracy and demonstrate the feasibility of our proposed method. Gas invasion experiments in conjunction with X-ray imaging on three different shales, i.e., Bakken, Haynesville and Marcellus shales, are reported. The average of measured in-situ xenon density within the Bakken, Haynesville and Marcellus shale samples were found to be 179.87kg/m3, 326.05kg/m3 and 947kg/m3, respectively, which are higher than xenon density in free space. This densification contributes to enhanced gas storage capacity in shales. The characterization of shale composition and pore structure were presented in order to associate this observed phenomenon with shale properties. The results indicated that pore structure is a better indicator of gas densification, while compositional properties are weakly correlated with gas densification.