Electrical Resistance Tomography for Monitoring Shallow Enhanced Recovery Processes

Abstract

Currently, Enhanced Oil Recovery (EOR) processes are monitored using gas analysis, geophysical logging, observation wells (P&T), well testing methods, seismic velocity tomography, or inversion of deformation measurements. These methods each have their strengths and weaknesses. Most EOR processes involve massive changes in the formation resistivity because of the introduction of a fluid phase with a different conductivity, or a large change in temperature. Three-dimensional electrical resistivity tomography may be a way of tracking propagation of fluid fronts with time. We present general requirements for resistivity tomography in EOR, typical electrode installations to reduce noise and seasonal variations, requirements for a general inversion of a 3-D resistivity problem in EOR, sensitivity analyses for a shallow reservoir case subjected to EOR, and a method of rapid design evaluation of resistivity monitoring. We believe that analysis tools and the technology is now adequate to reevaluate and develop electrical monitoring for EOR applications. Introduction Geophysical techniques have been used for reservoir delineation and description for several decades. Currently, attempts are being made in modifying geophysical techniques to actively monitor secondary and tertiary recovery processes such as water, steam, and fireflooding. It has been realized that the detection of changes in the geophysical response with time can be used to estimate the lateral extent and volume of the reservoir affected by enhanced recovery processes. The main objective of monitoring is to provide a reliable temporal description of the fluid front propagation resulting from the flooding. These data are usually supplemented with production and observation well histories to estimate reservoir recovery efficiency as well as to plan future continuation of production cycles. In fact, such data may even lead to improved process control because it provides an independent feed-back measure of the recovery behaviour. P. 183