Laboratory Testing on Geomechanical Properties of Carbonate Rocks for CO2 Sequestration

Authors: Xuejun Zhou (speaker), Zhengwen Zeng, Hong Liu, and Alyssa Boock, University of North Dakota.

Venue: 43rd U.S. Rock Mechanics Symposium and 4th U.S.-Canada Rock Mechanics Symposium, Asheville, NC, June 28-July 1, 2009. http://www.armasymposium.org/ [external site]

Abstract: The Williston basin of North Dakota is predominated by carbonate successions from Cambrian through Cretaceous, followed by episodic glaciations through Quaternary. Geomechanical characterization of this rock succession is a critical element for understanding the subsurface processes when conducting anthropogenic CO2 sequestration. CO2 sequestration can be divided into two stages. The first is to inject CO2 into the target formation; the second is to keep the injected CO2 in the formation for a designed period of time, e.g., 1,000 years. As rocks behave differently under deep reservoir conditions from how they behave under atmospheric conditions, detailed studies of thermo-hydro-mechanical effects are needed. In this paper, effects of CO2 sequestration on host rock are investigated through combined water-alternative-CO2 injection and tri-axial geomechanical tests. Testing results indicate that rock strength can be decreased significantly after the first stage. In the second stage, which is under static, no-flow conditions, there is no obvious difference in strengths between CO2- and water-saturated rocks. It seems that CO2 saturated rocks even tend to be more competent. This may reveal the different micro-cracking mechanisms caused by different molecular-level properties, such as wettability, etc. Linear Mohr-Coulomb criteria were applied to drained testing results very well but show discrepancies with those of un-drained testing.

Related NETL Project
This presentation is related to the NETL project DE-FC26-08NT0005643, “Geomechanical Study of Bakken Formation for Improved Oil Recovery.” The goal of this project is to determine the in situ stress and geomechanical properties of the Bakken formation and to use these results to increase the success rate of horizontal drilling and hydraulic fracturing to improve the ultimate recovery of this vast oil resource.

NETL Project Contacts
NETL – John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
University of North Dakota – Dr. Zhengwen Zeng (zeng@und.edu or 701-777-3027)