A Study On Remaining Oil Distribution Of Heterogeneous Thick Oil Reservoirs In High-water-cut Stage

At present,many oil fields in our country have entered the stage of ultra-high-water-cut.The remaining oil distribution becomes hardly to be predicted,with the high producing degree of reserves and the complexity of the condition of submergence.In view of this difficulty,the paper puts forward the comprehensive research of reservoir heterogeneity,which characterized the feature of oil reservoir heterogeneity qualificatively and quantitatively from several angles,combining with dynamic and static,macro and micro datas.It analyses the control factors of remaining oil during ultra-high-water-cut stage,and reveals the concentrating rules of remaining oil,offers scientific basis for adjustment and tapping potential of remaining oil.For the status of influence of oil reservoir heterogeneity to the recovery,the paper has researched the heterogeneity of classification at home and abroad. Acorrding to continental reservoir features in China, it proposed that heterogeneity was divided into macroscopic heterogeneity and micro heterogeneity, macroscopic heterogeneity included inner heterogeneity, interlayer heterogeneity and areal heterogeneity, micro heterogeneity included pore structural heterogeneity. In the research on geological features of the reservoir heterogeneity, it characterized the reservoir heterogeneity description qualificatively and quantitatively from the macro and micro aspects.On the micro heterogeneity study,predecessors always described pore structure with some parameters,such as uniformity coefficient,structure coefficient,separation coefficient and so on,but the micro pore structure can't be described by the single parameter.Based on this point,the paper puts forward the composite index of pore structure (SQRT (K/Φ)) creatively,which is used to research pore structure.The Core analysis result indicates that the composite index of pore structure shows exponetial grow with the average pore radius, with oil displacement efficiency is under the relationship of the increasing, degree of reserve recovery is also under the relationship of the increasing, and fractal dimension of composite index of pore structure follows an diminishing rule, which show that the bigger the numeric of fractal dimension is, the more complex fractal structure is, and the stronger heterogeneity is, the wores reservoir property is. The results show that the composite index of pore structure can really reflect microstructure distribution and characterize accuratly heterogeneous degree of miscroscopic pore structure.On the macro reservoir heterogeneity study,due to few research on relationship between micro pore structure parameters and macro pore structure feature,the paper creatively puts forward the research of the composite index of pore structure applied to inner heterogeneity research.According to analysis on the composite index of pore structure in layers from H3IV21to H3IV23, it is found that the bigger fractal dimension of the composite index of pore structure (SQRT (K/Φ)) in layers is,the stronger reservoir inner heterogeneity is. In the areal heterogeneity study, it analyses the fractal growing law of viscous fingering front using a stochastic simulation technique,it is found that the greater value of the viscosity ratio is, the less fractal dmension df and sweep efficiency is, which lead to earler water breakthrough in oilfield and lower oil displacement efficiency, and remaining oil in stream dirction inner well can be divided into isolated islands during the growing of viscous fingering which lead to high water cut, but degree of reserve recovery is low.In view of the research method of remaining oil distribution of heterogeneous reservoirs and existent insufficiency, the paper put forward the forecasting method of remaining oil distribution based on geological configuration, especially analyses and predicts remaining oil using the composite index of pore structure. Taking AnPeng district of ZhaoAo oilfield as an example, microscopic, plane and in-layer of remaining oil can be predicted through the composite index of pore structure, the same results can be obtained using numerical simulation, it is found that remaining oil distribution is usually in heterogeneous place where the composite index of pore structure is uneven and low, which matchs results of fractal growing law on viscous fingering front using a stochastic simulation technique. Combined with development characteristics of of ZhaoAo oilfield, it can decrease the resistance of well bore nearby and special attention is given to unifomity of the resistance in tapping measures of oil and water well, we can change stream dirction through well pattern adjustment, which can get better development effect for remaining oil potential tapping. The research method can offer new direction for prediction of remaining oil in the oilfield.