Permeability Evolution in Naturally- and Hydraulically- Fractured Microbially Enhanced CBM Reservoirs
Open Access
- Author:
- Zhi, Sheng
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 12, 2019
- Committee Members:
- Derek Elsworth, Dissertation Advisor/Co-Advisor
Derek Elsworth, Committee Chair/Co-Chair
Shimin Liu, Committee Member
Amin Mehrabian, Committee Member
Tong Qiu, Outside Member
Mort D Webster, Program Head/Chair - Keywords:
- Coalbed methane
Hydraulic fracturing
Natural gas production
Biogasification
Proppant embedment
Gas adsorption - Abstract:
- Microbially-enhanced coalbed methane (Microbial-ECBM) recovery is a novel method to stimulate methane yield in CBM reservoirs. To be effective, methanogens require that the nutrient solution must be delivered efficiently to a maximally large reservoir volume for microbial colonization. Hydraulic fracturing is the key to generate highly-permeable artificial fractures that facilitate nutrient sweep. Although many factors that influence hydraulic fracture propagation or permeability have been investigated for conventional and shale gas reservoirs, there still remain many unknowns in the implementation of hydraulic fracturing in CBM reservoirs. This is due to the unique characteristics of coal, including low strength and stiffness, the presence of abundant natural fractures and active gas adsorption/desorption. Both experiments and analysis (equivalent multi-continuum medium) are applied to investigate changes in critical fracture properties and resulting changes in the effective solute transport characteristics and nutrient delivery for different stimulation methods. The following questions are addressed in this study: (1) What is the potential to initially prop-open and then sustain the functionality of hydraulic fractures in coal and what are the key factors that control this (e.g. loading stress, confinement, and sorptive gas pressure) in Microbial-ECBM reservoirs? (2) What is the effectiveness of hydraulic fracturing in enhancing nutrient delivery and how does this inform Microbial-ECBM stimulation strategies (e.g. injection pressure, injection time, fracture connectivity, and propped permeability)? (3) What are the influences of CO2/Supercritical-CO2 (yielded by methanogens) on fracture permeability evolution during gas production?