Optimizing Water Injection Rates for a Water-flooding field

摘要

Setting proper water injection rates for the injection wells is a key factor to successfully operate an oil field under water flooding. The success of such activity could (a) reduce water cycling at field, section and pattern levels; (b) improve water/oil ratio (WOR) and areal sweep efficiency; (c) improve oil production and recovery by directing water injection to specific zones and areas; and (d) reduce OPEX by improving water utilization. Typically, the onsite engineers adjust injection rates using heuristics. While this does improve performance we feel that a more systematic approach can be developed which will lead to further gains. In this paper, we present a systematic method, using the linear programming, to optimize the water injection target rates. In this method, the reservoir is considered to be a system which can be modeled as a collection of continuous-time impulse responses that convert injection rates into a production rate. A very simple two parameter parametric model, like diffusivity-filter, has been used to quantify the injector-producer continuous-time impulse responses channel model and the Extended Kalman Filter has been used to establish the allocation factors between injectors and producers in the water-flooded field. Subject to constraints, including the total available water amount, the maximum and minimum injection rates, the maximum total production fluid for a producer and a gauge setting, a linear programming optimizer has been applied to determine the optimized water injection rate, based on the established allocation factors. This method was pilot tested on a Chevron oilfield for 3 months. The decline curve for 6 months and for 2 months of historical oil production data have been calculated. The 3 month pilot test result indicated that the optimized oil production matches the historical 6-month decline curve very well with about 22% less total daily water injection. Also we saw about 2% incremental production above the historical 2- month decline curve (again with about 22% less total daily water injection). These results suggest that this systematic method may provide a way to optimize the water injection target rates.