Cyclic Water Injection in San Jorge Gulf Basin, Argentina

Abstract

Abstract Historical production operations in San Jorge Gulf Basin have shown that production loss of down time, due to operational problems or any strikes can be recovered in the same production period of the year without changing any operational conditions. The study of the physical processes involved in this phenomenon has motivated the investigation on cyclic water injection. There is an extensive list of international references on cyclic water injection that can be traced back to the early 1960’ showing encouraging results on laboratory, simulation and field developments. Nevertheless, recently it has received renewed attention since for mature fields (i.e. after a long history of water injection) cyclic water injection now appears to be a very appealing option to conventional water flooding for it may lead to additional oil recovery at virtually zero additional cost. Many thin fluvial sands saturated with viscous heavy oil, high area-thickness ratio, long history of secondary flooding, high water cut, and low recovery factor reservoirs were the selected candidates for cyclic water injection. The main reasons for the improved oil recovery were found to be that cyclic injection schemes increase the sweep efficiency through oil migration on the high saturation gradient around swept zones, reducing water channeling and fingering by means of stabilization of the displacement front. In addition, by keeping injected water in the reservoir, its energy is raised, oil production is increased and water cut is reduced. In this paper, an alternative theoretical interpretation of the process is presented as well as simple simulation models of the heterogeneous and anisotropic sands distributions. Here we demonstrate that high oil incremental from cyclic injection is achieved even in total absence of capillary forces or heterogeneity. Besides, an exhaustive analysis of the main rock and fluid properties, cycle length and pressure conditions is performed. The on-going cyclic water injection project in Las Mesetas field in San Jorge gulf basin western flank makes use of the maximum injection capacity by distributing the cyclic injection vertically by mandrels and per wells in a fashion that keeps stable the total water injection rate from the water plant and maximizes cyclic injection potential. Simulation history match in a small region of the project area is used to exemplify the different possible responses. The field results proved the effectiveness of this process producing 11000 m3 of incremental oil in the firsts 18 months.