Geomechanical and Fluid-Flow Modeling to Estimate Disturbed Rock Zone Properties and Design Parameters for a Hydro-Mechanical Field Test in a Deep Borehole in Crystalline Rock
Abstract
Stress disturbance due to drilling a deep borehole in crystalline rock could lead to the development of a disturbed rock zone (DRZ) with altered hydro-mechanical characteristics surrounding the borehole. The presence of a DRZ could increase hydraulic conductivity and cause preferential flow in both the radial and the vertical direction around the borehole. Simulating fluid flow and mechanical processes due to drilling enables understanding characteristics of the DRZ including its thickness, radial distribution around the borehole, and pressure diffusion within DRZ. It also provides a tool for designing a hydro-mechanical field test to characterize the DRZ around a planned deep borehole. We modeled a hypothetical deep borehole in granite rock similar to a U.S.-mid-continent granite to simulate: (1) geomechanical processes involved in the creation of a DRZ caused by drilling; then, (2) subsequent fluid flow process by importing DRZ parameters (radius, heterogeneity) from the geomechanical model. The dual-model approach provides predictions of stress concentration and yield zone around the borehole from the geomechanical model and predictions of pressure diffusion in DRZ from the fluid-flow model. We also evaluated effects of increasing radial pressure, applied by packers placed inside the borehole, on vertical fluid migration in the DRZ. The importance of input parameters (rock mechanical, geological, and in-situ stress parameters) on DRZ extension and hydro-mechanical test design parameters was investigated using sensitivity analyses which showed that rock cohesion and differential horizontal stress are the most important parameters affecting DRZ radius extension (i.e., size).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H53D1738R
- Keywords:
-
- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1835 Hydrogeophysics;
- HYDROLOGYDE: 1859 Rocks: physical properties;
- HYDROLOGYDE: 4430 Complex systems;
- NONLINEAR GEOPHYSICS