Investigation of novel geophysical techniques for monitoring CO2 movement during sequestration

摘要

Cost effective monitoring of reservoir fluid movement during CO{sub 2} sequestration is a necessary part of a practical geologic sequestration strategy. Current petroleum industry seismic techniques are well developed for monitoring production in petroleum reservoirs. The cost of time-lapse seismic monitoring can be born because the cost to benefit ratio is small in the production of profit making hydrocarbon. However, the cost of seismic monitoring techniques is more difficult to justify in an environment of sequestration where the process produces no direct profit. For this reasons other geophysical techniques, which might provide sufficient monitoring resolution at a significantly lower cost, need to be considered. In order to evaluate alternative geophysical monitoring techniques we have undertaken a series of numerical simulations of CO{sub 2} sequestration scenarios. These scenarios have included existing projects (Sleipner in the North Sea), future planned projects (GeoSeq Liberty test in South Texas and Schrader Bluff in Alaska) as well as hypothetical models based on generic geologic settings potentially attractive for CO{sub 2} sequestration. In addition, we have done considerable work on geophysical monitoring of CO{sub 2} injection into existing oil and gas fields, including a model study of the Weyburn CO{sub 2} project in Canada and the Chevron Lost Hills CO{sub 2} pilot in Southern California (Hoversten et al. 2003). Although we are specifically interested in considering ''novel'' geophysical techniques for monitoring we have chosen to include more traditional seismic techniques as a bench mark so that any quantitative results derived for non-seismic techniques can be directly compared to the industry standard seismic results. This approach will put all of our finding for ''novel'' techniques in the context of the seismic method and allow a quantitative analysis of the cost/benefit ratios of the newly considered methods compared to the traditional, more expensive, seismic technique. The Schrader Bluff model was chosen as a numerical test bed for quantitative comparison of the spatial resolution of various geophysical techniques being considered for CO{sub 2} sequestration monitoring. We began with a three dimensional flow simulation model provided by BP Alaska of the reservoir and developed a detailed rock-properties model from log data that provides the link between the reservoir parameters (porosity, pressure, saturations, etc.) and the geophysical parameters (velocity, density, electrical resistivity). The rock properties model was used to produce geophysical models from the flow simulations.