Abstract

The possibility of using polymer gels for improved conformance in the treatment of producer wells has been evaluated using computer simulation. A radial model was built and used to test a variety of immiscible displacement conditions. The tests included water influx in a layered clastic reservoir with and without segregation between layers, simultaneous water and gas coning in a uniform carbonate reservoir, and simultaneous water and gas channelling in a fractured carbonate reservoir. The gel placement was modelled by altering the permeability, or the relative permeability, of the affected blocks according to experimentally determined values. Reverse coning was also evaluated for the case of simultaneous water and gas coning.

This preliminary design work has proved that utilization of polymer gels in producers is favoured in clastic reservoirs when there is segregation between layers. It also proved that gels have little value when implemented in a uniform carbonate reservoir producing under high water/oil ratio. Gel placement extended production well life by significantly reducing water/oil ratios and gas/oil ratios, but cumulative oil production did not increase in proportion to well life. Injection of a plugging agent around the perforations can be detrimental to oil production if the plug is too large. Finally, reverse coning was found to be more effective than gel placement for the case of simultaneous water and gas coning.

Introduction

The concept of increasing conformance through the injection of polymer gels has been the topic of extensive research and numerous reviews. Water coning in oil wells has been the main focus of earlier research but gas coning is becoming of increasing interest. Recently, water coning in gas wells has also attracted attention. Although the problem focusses on producer wells, most of the successful treatments documented in the literature were applied on injectors. Reservoir conditions, gel properties and placement protocols influence how effectively gel treatments reduce water coning(1, 2). Although success has been demonstrated both in the laboratory and in the field, no one is in a position to claim a good understanding of why gels work so well in some situations and not in others(2).

The majority of gels used today are either polyacrylamides(3, 4) or polysaccharides. However, simple polymer injection was considered for controlling water influx in horizontal wells placed in heavy oil reservoirs(5). Other technologies include use of nitrogen(6), starch biopolymers(7), silicates(8), surfactant and alcohol Blends(9), small particle cement(10), to name only a few of the recent applications. Of particular interest is the work that aims at selective relative permeability alteration so that water influx to the production wells is hindered. The technology can be applied to both oil and gas wells(11, 12). Recently, the combination of foams and gels seems to provide hope for extended use of gel technology(13, 14). Coupled with the laboratory findings, extensive field results have been presented by Marathon Oil(4), Phillips Petroleum(15), etc., where the effectiveness of gel technology has been mainly demonstrated for treatment of injector wells in waterflood scenarios of fractured reservoirs.

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