Design And Field Trial Application of Foam In Production Wells to Improve Conformance

Abstract

Abstract Many of the hydrocarbon vertical miscible floods in the Keg River carbonate reefs of the Rainbow Field are at a mature stage, of reservoir depletion, and are characterized by thin oil sandwiches, high gas recycle and declining oil production. Under these adverse conditions, conventional workover techniques to control gas recycle and improve oil productivity have diminishing success. In considering alternative strategies to reduce gas coning, Husky felt that injection of a gas-blocking foam barrier into a gas cone hadthe potential to be a cost-effective treatment. This paper describes the experimental foam treatments conducted on two production wells, each in a different miscible flood pool. Aspects of the laboratory work, numerical coning simulation, well selection process and foam placement strategy that went into the field treatment design are presented. On one well, the foam-forming surfactant was injected as an aqueous solution to allow in situ foam generation, and also as a surface generated preformed foam. Neither method was successful in improving the performance of this well. On the other well, where only preformed foam was injected, the treatment was successful in reducing gas-oil ratio (GOR) and improving-oil production over a 14 month period. Much of the experience gained from the field treatments will facilitate the efficient planning, design, implementation and evaluation of future foam projects. Introduction Husky Oil Operations Ltd. operates a number of mature hydrocarbon vertical miscible floods in the Keg River carbonate reefs of Rainbow Field, Alberta, Canada. Many of the wells in these floods are already completed at or close to the base of the remaining oil sandwich, and are experiencing increasing solvent/chase gas coning and declining oil productivity as the oil zone thins under continued injection and production. With little or no room to move in the oil pay, conventional workover strategies of cement squeezing and reperforating lower have diminishing application. In evaluating innovative methods to mitigate gas production, foam chemicals were considered. The potential of foam as a blocking or mobility reduction agent to gas flow has been well documented(1–5). Due to potentially high adsorption losses, foam only has a chance of working from the injection side if it is able to reduce mobility in a relatively small channel volume between injection and production wells, or if the channel is isolated from the rest of the reservoir away from the injection well (minimum volume of rock contacted). However, most of the Keg River reefs have relatively good communication throughout, and in most FIGURE 1: Keg River "A" Pool. Keg River structure contour map. Available In Full Paper. cases, tracing has shown the channels to be relatively large. Consequently the focus was diverted away from an expensive, large volume foam treatment at an injector to a much smaller, near wellbore treatment at a producer. Adsorption of foam-forming surfactant onto reservoir rock would not be a big problem if the amount of rock contacted could be kept to a minimum.