Study On The Remaining Oil Distribution And Digging Potentional After Polymer Flooding In High Water-cut Reservoir

The polymer flooding technology is a method of tertiary oil recovery for the reservoirs with high water-cut. Reservoirs produced by the first recovery, the second recovery and tertiary recovery are faced with some issues on improving oil recovery further. This paper presents the study of remaining oil micro-distribution and oil displacement status between high and low-permeability layers by laboratory physical simulation, which is based on geological features of reservoir structure, sedimentary microfacies, interlayer, and heterogeneity, as well as polymer flooding development characteristics, which takingⅡ4-5 layers in north fault-block of Shuanghe oilfield as an example. The law of remaining oil distribution is ascertained after polymer flooding, by numerical simulation, typical heterogeneous conceptual model, reservoir dynamic analysis, coring and well testing. The article analyzes geological and development factors which control the remaining oil distribution, classifies the remaining oil, evaluates potential oil, put forward the suggestion of tapping methods after polymer flooding and provides the results of oil displacement experiment and pilot test project design. The main research results are as follows:1. Set up three technology indexes systematically which are related to increasing oil production, decreasing water production and flooding process validity to evaluate development effect, and supply evaluation methods of various indexes, which are based on the development features of polymer flooding in high water-cut reservoir.2. Find polymer flooding improvement on low permeability layers, and the difference between the high and low permeability layers reduced, but the difference still existing, after research of laboratory physical simulation, typical heterogeneous conceptual model, and well testing data inⅡ4-5 layers; the permeability difference influences the oil recovery between high and low permeability layers, and the bigger the permeability difference, the larger the oil displacement difference are; point out that the low permeability layers still have great potential to enlarge volumetric sweep efficiency.3. Put forward two factors influencing the remaining oil, that is, geological factors and development factors after analyzing volumetric sweep efficiency of polymer solution. classify the remaining oil into six types, namely, updip pinchout zone with imperfect well pattern, the area away from the main stream line, pressure balance area,small oil sand bodies, fine sedimentary rhythm, and low permeability layers.4. Synthetically apply multi-technology such as reservoir numerical simulation, reservoir dynamic analysis, coring and well testing data, further put forward the remain geological reserve ofⅡ4-5 layer of north fault-block mainly located in pay zones with thick oil and more superposition layers, and think the main pay zones are the target of improving oil recovery after polymer flooding.5. Put forward the potential-tapping technology, namely, chemical combination flooding method combined with conventional methods to enhance oil recovery after polymer flooding in high water-cut reservoir. In chemical combination flooding patterns, little cross-linked polymer plug can enlarge volumetric sweep efficiency of low permeability layers, and surfactant/polymer combination system can decrease surface tension between oil and water and improve flooding efficiency of low and high permeability layers. The laboratory physical simulation and pilot test project design indicate that chemical combination flooding method can increase oil recovery further after polymer flooding.