No abstract

The issue of increasing reservoirs recovery rate in non-uniform permeable high-viscosity oil reservoirs is considerably challenging, especially when the oil under reservoir conditions manifests its structural-mechanical properties, which is characteristic of the Buzachi North oil field. Its development using water flooding method has demonstrated that even moderate uptake of recoverable reserves is followed by injection water breakthrough to the production wells. As substantiated by the high median permeability quotient with a broad range of values, employment of a regular ("classical") polymer flooding technique for the task of aligning the oil displacement front, when instead of water a weak polymer solution is injected in high volumes (up to 30 % of pore volume), is of similarly low efficiency because of rapid polymer breakthrough to the production wells boreholes through fissures and "super reservoirs". This article presents development and field pilot tests results related to cyclical gel polymer flooding technology as applied under the conditions of the Buzachi North oil field productive reservoirs rich in high-viscosity oils. The technology implies an integral gel polymer action upon water-bearing strata of productive reservoirs via injection wells performed in several stages. During the first stage, fissures are isolated with water-swellable polymers or synthetic resins; during the second stage, profile log is aligned using high-viscosity hydrogels; finally, during the third stage, the oil is displaced with a low-viscosity hydrogel slug based on cross-linked acrylamide polymer. Based on laboratory and field research, optimal linear dimensions (fractions) of water-swellable resins have been selected, along with cross-linkers and their concentrations required to obtain high-viscosity gels under reservoir conditions; the optimal amounts of low-viscosity hydrogels to be injected at the displacement stage have been determined. The parameters of fissures and "super reservoirs" required for estimating the working amounts of injected gels at each stage are evaluated by means of tracer analysis performed immediately prior to the injection cycle start. The tests performed at 16 sites with Jurassic deposits and two sites with Cretaceous deposits of the Buzachi North oil field have demonstrated high technical and economic efficiency of the developed cyclic gel polymer flooding technology.