DE-FE0006011

Goal
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.

Performers
Sky Research, Inc., Ashland, OR 97520
Pacific Northwest National Laboratory (PNNL), Richland, WA 99352

Background
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 ten 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 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 for 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 on 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 electromagnetic methods to be deployed and used in an integrated, cost-effective manner in CO₂ EOR sites.

The core of the system developed in this project will be a novel high performance Time Domain Electromagnetic (TDEM) receiver which will be developed by Sky Research. 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.

Impact
The impact of this project will be to provide cost effective tools to account for CO₂ as it is being injected in the subsurface near real time and allow for better control of CO₂ floods so as to optimize enhanced oil recovery. This capability will directly impact next generation CO₂ EOR efforts as it will provide 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.

Accomplishments
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 both with gravity, active seismic, electrical, and electromagnetic 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.

For the gravity software code, an initial forward modeling MATLAB (matrix laboratory) code was developed based on code descriptions from the literature. The project team is developing site specific petrophysics relationships using the geological and geophysical well logs data to evaluate this code.

Current Status (January 2012)
The focus of the CO₂ modeling effort is the use of electrical, gravity, and electromagnetic modeling codes to model signal response. So far, the focus has been on the modification and preparation of the existing codes to be able to ingest the results from the PNNL models. Specific CO₂ EOR model scenarios for a range of different geophysical systems using the existing PNNL-developed code are being performed. For the electromagnetic modeling software code, two codes developed by the project team are being evaluated. The first code uses the method of auxiliary sources (MAS) to solve the wide band electromagnetic induction problem. The second code is a more conventional finite element code.

The geophysical sensor system design is being initiated. The project team is evaluating the use of commercial and/ or in house developed hardware for resistivity, electromagnetic, and gravity data. The feasibility of integrating gravity gradiometers and borehole resistivity in the existing system is also being evaluated. Discussions are being held with different manufacturers as to the cost and availability of different hardware elements needed to compliment the geophysical sensor system to be deployed for EOR monitoring in the field.

Project Start: February 1, 2011
Project End: January 31, 2014

DOE Contribution: $741,474
Performer Contribution: $185,366

Contact Information:
NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 281-494-2488)
Sky Research – Roelof Versteeg (roelof.versteeg@skyresearch.com or 650-521-2587)
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