Combining Small Well Spacing With Polymer Flooding To Improve Oil Recovery of Marginal Reservoirs

Abstract

Because of low volumetric sweep efficiency and large difference in injection and production rate of each zone, the recovery factor of water flooding is very low in some continental and heterogeneous sandstone oil fields, especially when the reservoir continuity is poor, permeability low and high permeability variation between different zones. Due to the amount of incremental producible oil is not large enough to further drill infill wells economically, drilling infill wells and performing polymer flooding simultaneously was proposed and a pilot test has been concluded. The paper introduces the laboratory studies on selection of polymer injection parameters and project design optimization. According to these studies, a pilot test of "Combining Small Well Spacing with Polymer Flooding" was conducted. The well spacing is 100 meters, the zones with a thickness of less than 1 meter and with a permeability rage of 5 to 100 md were combined together and put on development. Both lab studies and pilot results show that the volumetric sweep efficiency was greatly increased, especially after applying separate zone injection measures in polymer injectors based on injection profile surveys and tracer test data. The pilot test indicates that the technique of combining infill wells with polymer flooding is economically feasible with 10% OOIP incremental recovery at a production cost of $10/bbl. INTRODUCTION In continental, multilayer and heterogeneous sandstone oilfields, some reservoirs with poor connectivity and low permeability have lower recovery factors. The low degree of connection of layers between wells and inner-layer interferences lead to high watercut for waterflooding and poor effenciency for increasing the recoverable reserves of single wells. In order to further enhance the oil recovery and increase the oilfield's recoverable reserves, we drilled infill wellpatterns and performed polymerflooding simultaneously to improve the combined economic benefits of marginal reserovir. The main idea of the technology is to adjust the reservoir connectivity by drilling infill wellpatterns, and then inject a polymer solution. On the basis of waterflooding, polymerflooding could further increase some amount of recoverable reserves. The technology of combining dense wellpattern with polymerflooding will not only improve oil recovery but also obtain better economic benefits. Therefore, we implemented the pilot test in the oilfield and also applied separate-layer injection and stimulation measures during the test, which achieved good results with average incremental oil per day for a single well 1.83 times that of the original production, watercut decreased 10.2% and oil recovery increased more than 10%.