The objective of this project is to design, develop, and validate a real-time, semi-autonomous geophysical data acquisition and processing system using electromagnetic technology to monitor carbon-dioxide (CO2) flood performance.
White River Technologies, Ashland, OR 97520
University of British Columbia (UBC) Vancouver, Canada
Next generation carbon-dioxide enhanced oil recovery (CO2 -EOR) technology requires accurate and cost-effective instruments and technology that can detect the spatiotemporal emplacement of the CO2 in the reservoir and measure its subsequent movement and resulting changes in physical and chemical states. Theoretical, laboratory, and field efforts over the past 10 years have provided scientific and field validation of the applicability of a range of indirect (geophysical) methods for CO2 -EOR and CO2 storage reservoir monitoring. While further research is ongoing to enhance the quantitative interpretation (in terms of changes in physical properties) of these remote measurements, there is a reasonable agreement on the applicability and sensitivity of indirect methods such as active and passive seismic, geodetic methods (INSAR/tiltmeters), and gravity, electrical, and electromagnetic (EM) methods.
Four-dimensional reflection seismic is the dominant method used for monitoring at several commercial CO2 sites (Sleipner, Weyburn, and In Salah). It is generally recognized that while 4-D seismic is a good tool to monitor emplacement and subsequent movement of CO2, it cannot in itself provide a mass balance, and may not be a good tool for long-term monitoring due to the associated costs as well as the sensitivity of seismic data to changes in source and receiver characteristics. However, other methods such as passive seismic, electrical resistivity, time domain electromagnetic, geodetic measurements, and gravity are sensitive to CO2 spatiotemporal behavior and are better suited for application of a long-term monitoring approach. Each of these methods provides complimentary information. For instance, passive seismic data can be used both for injection-related earthquake monitoring and for interferometric imaging. Gravity can provide a mass balance and information about migration. Tiltmeters provide information on deformation, whereas electrical and electromagnetic methods can provide information on flow, mineralization, and bulk movement. Note that CO2 flooding has been shown to be associated with substantial changes in electrical properties and that time-lapse imaging of electrical properties is thus especially promising as an approach to image CO2 flooding. If applied in typical geometries and stand-off distances, none of these methods would have enough sensitivity to provide required information about CO2 movement with sufficient precision. While the applicability of seismic methods to track CO2 emplacement and movement has been demonstrated at commercial injection sites and several pilot sites, no clear framework currently exists that allows for EM to be deployed and used in an integrated, cost-effective manner at CO2-EOR sites.
The core of the system to be developed in this project will be a novel high performance Time Domain Electromagnetic (TDEM ) receiver. The remaining system will consist of commercially available geophysical sensors, the specific configuration of which will be decided during the project, but which may include passive seismic sensors, tiltmeters, gravity sensors, and electrical geophysical systems. These geophysical sensors will be integrated with data acquisition units that will be deployed in an autonomous, continuous monitoring mode. The data acquisition hardware will be integrated with middleware to provide data transmission to a server for automated data processing on a high-end cluster. The result of geophysical inversions will be linked to PNNL-developed reservoir modeling software to provide for near real time estimates of CO2 flooding.
The impact of this project will be to provide cost-effective tools to account for CO2 as it is being injected into the subsurface in near real time and allow for better control of CO2 floods so as to optimize EOR. This capability will directly impact next generation CO2-EOR efforts by providing tools for quantifying CO2 and optimizing reservoir performance (i.e., control the actual flood). If the proposed technology is successful, it would substantially increase the viability of next generation CO2-EOR projects.
A literature review on the feasibility of CO2-EOR monitoring using a range of different geophysical sensing modalities has been completed. Theoretical, numerical, and field-based evidence exist that CO2-EOR emplacement can be observed and monitored with gravity, active seismic, electrical, and EM methods. There is a good agreement between the actual magnitudes of changes observed in the geophysical field data and theoretically predicted values. This indicates that numerical methods can be used effectively to predict the efficiency of CO2-EOR geophysical monitoring.
Numerical simulations using reservoir models of candidate test sites indicated that a surface-deployed EM system would not produce measurable responses as significant EM noise is generated from infrastructure on the surface. Deployment of both transmitters and receivers down-hole will allow improved imaging of the reservoir and isolates the system from noise sources. White River Technologies is currently constructing a cross-borehole EM system designed for geophysical monitoring of subterranean changes in conductivity. The system includes a large transmitted dipole moment operating between 100 Hz and 1 KHz and a very sensitive receiver system.
The project, which was originally awarded to Sky Research, was to be transferred to White River Technologies. White River was unable to secure the remaining cost share to complete the award; therefore, the project will end.