WATERFLOOD TOMOGRAPHY: MAPPING HIGH CONTRAST PERMEABILITY STRUCTURES USING INJECTION/PRODUCTION DATA

The paper presents a novel analytical method to detect the existence and orientation of high contrast permeability channels between injection and production wells in a waterflood. Unlike regular transmission tomography where complete response measurements are taken from all the angles, we have developed new algorithms to image the high contrast permeability structure by using production /injection data. The viewing angle is restricted from injectors to producers. The main advantage is this technique can be applied without significantly affecting daily operation and provide a consistency check with results from other methods. There have been suggestions made in the literature to use tracer or pressure transient data for imaging heterogeneous reservoirs (D.W. Vasco 1999, A. Al‑Ghamdi 1996). In our approach, we show the response times at the producers can be estimated by monitoring gross production rates, given that known time‑varying injection rates are applied. We propose a mixture model to characterize the response time, where multiple candidates of high contrast permeability channels are assumed to be the initial estimated structure. Our algorithm iteratively modifies the length, orientation and location of each high/low anomalous permeability structure to match the measured response time. Instead of providing a single solution for the location of high/low permeability channels, our method provides several possible estimates and make it possible to check with known geophysical properties. To validate our approach, we used a commercial simulator to test a 5‑spot waterflood and a line drive. In the first case, we tested a five spot from a low permeability reservoir with a centrally located producer that has been hydraulically fractured to enhance its productivity. Then we tested a single fracture with 45 degree orientation located between rows of producers and injectors. Results show our method can provide very accurate estimates of fracture orientation.