CO2 and N2 injection to enhance shale gas recovery

Open Access
Author:
Li, Ziyan
Graduate Program:
Energy and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 01, 2016
Committee Members:
  • Derek Elsworth, Thesis Advisor
  • Shimin Liu, Committee Member
  • John Yilin Wang, Committee Member
Keywords:
  • enhance shale gas recovery
Abstract:
Shale gas has become an increasingly important source of natural gas in the United States over the last decade. The application of two key techniques, horizontal drilling and hydraulic fracturing, have made it possible to extract gas economically from shale. Despite this, field production data show a rapid decline in gas flow rate after a few years of production. This drawback has focused attention on methods to enhance shale gas recovery (ESGR). In this work, we develop dual-porosity, dual-permeability finite element models to simulate multicomponent gas flow in porous media coupled with shale deformation and sorption behavior. We use this to explore the injection of pure CO2, pure N2, and mixtures of CO2 and N2 for enhanced recovery of shale gas. This behavior necessarily includes the evolution sorption-induced strain by competitive adsorption and its influence on permeability of matrix and fractures to ultimately define cumulative production history of CH4. This also defines the pattern of stranded CH4 concentration within the matrix after production under different injection conditions. It is shown that CO2 and N2 can each enhance shale gas recovery, but as a result of different mechanisms. Injected CO2 has a higher affinity than CH4 and thereby desorbs CH4; this technique can increase shale gas recovery by ~20%. Injection of N2 works as an ESGR because N2 lowers the partial pressure of CH4 in shale and thereby desorbs shale gas from the matrix for the lower absorbability of N2 with respect to CH4, which will enlarge fractures as well as shrinking the matrix; this method can increase shale gas recovery by ~80%. Injected mixtures of CO2 and N2 will result in shale gas recovery of between the end-member magnitudes 20% to 80% (injection of CO2 to injection of N2). Injected mixtures with a higher N2: CO2 ratio result in a greater recovery of shale gas.