The Feasibility Studies of Polymer Foam Flooding in Gudao Oilfield

Abstract

Abstract Gudao oil field is one of the major production areas in Shengli Field. After 20-year development, most of reservoirs are characterized by high water cut, poor sweep efficiency and inefficient oil recovery due to the high heterogeneity. The goal of this paper is to present the results of laboratory and field studies of polymer foam flooding in Gudao oilfield. For polymer foam, the displacement medium is N2 mixed with surfactant as foaming agent and polyacrylamide. Polymer foam can increase the sweep efficiency and control gas mobility by selective gas blocking and high apparent viscosity. The experimental investigation studied the use of additives to enhance foam properties and the factors affecting blocking performance such as injection model, gas liquid ratio, and alternate slug, etc. The oil displacement experimental results showed that the previous bypassed low permeability areas in polymer flooding could be swept by polymer foam displacement, and thus increasing oil recovery. The scaled-up laboratory data has been successfully applied in a field test. After 3 months of injecting polymer foam, the daily oil production increased from 75.1 t/d to 141.4 t/d, while water cut decreased from 93.9% to 88.1%. The above results demonstrate that enhanced foam flooding is a promising method for producing highly heterogeneous reservoirs and to improve the reservoir sweep efficiency after polymer flooding. Introduction Foam is extensively applied in steam flooding1–4 and CO2 flooding5–7 to enhance oil production, but as flooding technique for the conventional reservoir reports about lab study and field test are limited.8–10A combination system, which consists of surfactant, polymer and gas(such as N2, CO2, natural gas, etc.) is named as polymer foam flooding. The polymer foam flooding can channel selectively11,12 through high permeability zones and its apparent viscosity is greater than any other displacement medium13 to improve sweep efficiency during flowing in porous media. Meanwhile, it also can further enhance oil production by mixing surfactant with crude oil to make emulsification to displace more remanent oil in reservoir. In field test, co-injection and Liquid Alternating with Gas (LAG) were all practiced. But for actual injection ability, only LAG could realize polymer foam flooding injection. Lab study and field test in Gudao oil field proofed that polymer foam flooding is a promising technique for high heterogeneous reservoir. Experimental Apparatus and Procedure All flooding experiments were performed at the reservoir temperature of 70? under 6.0MPa of pressure. The schematic diagram of flooding apparatus is depicted in figure 1. Foam agent DP-4 and polymer solution and N2 were all injected into the core at a certain injection mode. Pressure drop between the endsof core indicated the blocking ability of foam agent, and the increased pressure drop showed effective block producing in the core. Resistance Factor(RF) representing blocking ability was the ratio of pressure drop betweenthe ends of core after foaming to pressure drop of water flooding. In laboratory study, there are two different groups of displacement model. In one group of displacement model the core is sand-packed stainless steel tube with 0.6m long and 0.025m diameter and oil displacement experiment was performed on such cores. This model consists of two parallel cores which are injected together and produce separately. In the other group of displacement model the core is bead-packed long slim stainless steel tube with 6m length, 0.045m diameter and permeability of 23.0µm2, and related experiments do not exist crude oil. Results and Discussion Blocking ability study of polymer foam flooding Blocking ability of polymer foam flooding has close relationship with core permeability, injection mode, ratio of gas to liquid, and alternative slug size. The influence factors are very important to design reservoir development project. So the influence law of these factors must be known. The following experiments are made on single sand-packed stainless steel tube.