document

Paper Number	08-329
Title	Laboratory Observation of CO2 Phase Transition Induced Seismic Velocity Change
Authors	Jakupi, A., Bigelow, T, Zeng, Z., Kringstad, J., Belobraydic, M., and Zhou, X, University of North Dakota; Grigg, R.B., New Mexico Tech
Source	The 42nd U.S. Rock Mechanics Symposium (USRMS), June 29 - July 2, 2008 , San Francisco, CA
Copyright	2008. American Rock Mechanics Association
Language	English
Preview	ABSTRACT: CO2 is injected into deep geological formations for enhanced oil recovery and/or for sequestration. For ideal results, CO2 is designated to be kept in the formation in supercritical state, pressure and temperature above the critical point (1071 psia and 88°F). Due to geological heterogeneity and changes in injection operation, the pressure or temperature might fall below the critical point in some parts of the formation. This will cause CO2 transition from supercritical to subcritical. Seismic methods have been considered promising for monitoring the distribution of injected CO2 under supercritical state. Can this method be used to monitor CO2 state change? This paper presents experimental results for an Indiana limestone core sample saturated with CO2 at 1100 psia (above critical pressure) and subject to axial and radial confining pressures of 3200 psia. We observed systematic changes in the compressional and shear wave velocities as the sample was heated and cooled across CO2 critical temperature. These results suggest that seismic methods have the potential to monitor remotely temperature-induced CO2 phase transition in subsurface geological formations. 1.INTRODUCTION Carbon dioxide (CO2) has been widely injected into mature petroleum reservoirs for enhanced oil recovery (EOR) since the early 1970s [1]. Storing CO2 in depleted oil and gas reservoirs, unminable coal-bed seams and deep saline aquifers is considered one of the most effective options for carbon management [2]. In order to improve sweep efficiency for optimized EOR results and to maximize carbon sequestration capacity in unit formation volume, CO2 is injected as supercritical fluid at pressures and temperatures above the critical point of1071 psia and 88°F. More CO2 can be stored in this dense state for long term storage in geologic formations with supercritical pressure and temperature conditions. However, geological heterogeneity, CO2-rock interaction, and inadequate injection procedures might change the CO2 in the formation from supercritical to subcritical, which could eventually ruin EOR orsequestration projects [3]. To prevent this from occurring, a tool that can be used to monitor both the space distribution and the phase status of the injected CO2 is needed. Seismic imaging has been considered as one of the most promising methods for monitoring injected hydraulic fracturing fluid and CO2 in petroleum reservoir formations [4, 5]. Whether or not this tool can be used to monitor CO2 phase change depends on the existence of detectable change in seismic velocities during CO2 phase transition. This paper presents the results of study to experimentally investigate if compressional (P-) and shear (S-) wave velocities change when a CO2 saturated Indiana limestone sample is heated and cooled across the CO2 critical temperature while the pore pressure is maintained above the critical pressure. 2.EXPERIMENTAL SYSTEM Laboratory experiments to investigate the change of seismic velocities of a rock due to CO2 phase transition can be performed using an in-house developed multipurpose triaxial acoustic core flooding system [6]. Figure 1 shows the system diagram with some individual components. The core represents a sample material cored from a reservoir well. This sample can be under varied geological conditions such as temperature, in-situ stresses, pore pressure, fluids, etc.
Number of Pages	16
File Size	506 KB
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