Study On Prediction Method Of Natural Productivity In Low Saturation Reservoirs

With the continuous exploration and development of oil fields,more and more low-saturation oil reservoirs have been found,because low-saturation oil reservoirs have great exploration potential,and the oil and gas production is also very considerable,therefore,it has become one of the important targets of oil field exploration and development at home and abroad.Because of the complex pore structure,low oil saturation and the same production of oil and water in low saturation reservoirs,it is very difficult to evaluate the fluid property and predict the natural productivity.The conventional method of calculating oil-water relative permeability has a low precision,which leads to a large error in predicting the natural productivity of oil-water two-phase fluid based on relative permeability,and can not meet the actual needs of oilfield development.It is necessary to establish a set of natural productivity prediction methods for low saturation reservoirs,which is of great significance for the effective development of low saturation reservoirs.The study area is a typical low saturation reservoir with poor physical properties,small pore throat radius,poor pore connectivity,complicated oil-water distribution and no uniform oil-water interface,all these bring a lot of difficulties to the identification of reservoir fluid properties,and make it more challenging to evaluate the productivity accurately.In order to improve the accuracy of productivity prediction and avoid the problem of large error of productivity prediction caused by facies permeability,this paper,based on the analysis of the "four properties" of reservoir,aiming at the actual characteristics of the low saturation reservoirs in the study area,firstly,the capillary pressure curve is used to classify the reservoir,and the pore structure parameters of each type of reservoir are extracted.To some extent,the problem of electric promiscuity between fluids has been overcome,the electrical parameters sensitive to oil-water two-phase fluid are optimized,and the oil-water layer identification plates suitable for different reservoir types are established.The plate precision is over 90% and the map posterior precision is over 80%.The fluid property of the reservoir is divided accurately,which lays an important foundation for the subsequent prediction of natural productivity,and the permeability of the reservoir is a key parameter to determine the accuracy of the prediction of productivity,a quantitative interpretation model of reservoir effective permeability is established by using flow unit index classification.The average relative error of permeability after classification is 46.7%,and the calculation accuracy is obviously improved.Finally,based on the actual oil test data in the study area,on the basis of accurately predicting the reservoir fluid properties,and aiming at the oil and water layers of single-phase fluid,the natural productivity of pure oil layer and pure water layer is calculated by the natural productivity formula of plane radial flow,and the oil production and water production of oil-water layer are calculated by the empirical formula method for oil-water two-phase fluid reservoir,and then get the liquid yield of the whole reservoir.Finally,a complete set of natural production prediction methods for different types of reservoirs and different fluid properties is established,which effectively overcomes the problem of large production prediction error caused by inaccurate relative permeability calculation.Using the actual oil testing data for back-to-back test,the whole set of low saturation reservoir productivity prediction method set up in this paper is suitable for productivity prediction in this area,the accuracy of prediction is over 85%.Therefore,the reliability of this set of production capacity forecasting method is confirmed,and it can also provide important theoretical basis for the next development and deployment in the region.