Velocity measurements in reservoir rock samples from the SACROC unit using various pore fluids, and integration into a seismic survey taken before and after a CO2 sequestration flood

Abstract

The SACROC field, located in west Texas in the Permian Basin, is t he oldes t CO2 enhanced oil recovery site in the United States, with over 93 milli on tons of CO2 injected as of 2007. Recently, t he Na tional Energy Technology Labora tory (NETL) of the United Sta tes Department of Energy has begun to support an enhanced oil recovery project at the SACROC field in north central Texas, working in close collaboration with the Bureau of Economic Geology in Austin, Texas. The project requires the injection of CO2 at a depth of approximately 2040 meters into a reef structure. This project involves both repeat reflection seismic surveys and rock physics based analysis of core material. In the SACROC field, hydrocarbons were flooded out using water, and will be flooded w ith liquid CO2 during the summer of 2008. An experiment is planned whereby we first image fluid floods through reservoir rock using a CT scanner at NETL in order to see what the residual saturations of the previous fluids are. We th en plan to conduct velocity measurements in this order, so that we can obtain a good estimate of conditions in different parts of the reservoir. W e will then measure the P and S wave velo cities, porosity, and permeability at varying pressures and temperatures that simulate reservoir conditions after each successive flood. In addition to velocity ulus, Poisson’s ratio, and stress and strain measuremen ts, we will measure porosity, permeability, Young’s Mod measuremen t under simulate d in situ reservoir conditions. Preliminary P and S wave velocity measurements were made in dry Berea sandstone samples in order to have a base r eference material to compare our results to. Our Berea measurements were 2402 m/s for Vp, 1688 m/s for Vs, and 0.703 for Vs/Vp for an unstressed sample, which agrees well with the literature. The measured ve locities, the P and S waveforms, the velocity vs. confining pressure will be used to calibrate our acoustical measurements both in dry and saturated samples of the carbonate SACROC reservoir rock using oil, gas, water, and CO2. We then plan on doing the first of several seismic surveys in the SACROC field in west Texas. The first survey will be comple ted during the summer of 2008, and presented at this meeting. Using our velocity measurement s, we hope to be able to discern the difference between areas of the reservo ir rock that are saturated with different pore - filling phases. With repeated surveys over the next few years, we hope to be able to observe the area of extent of various floods of CO2 that are scheduled to be injected into several wells in the area using the laboratory me asurements we collected.