Study On The Law Of Oil Production Decline And The Countermeasures Of Improving Oil Recovery In ST Reservoir

The ST reservoir is a high porosity and high permeability sandstone reservoir dominated by delta plain,fluvial facies and turbidite facies.It has been 52 years of development history since it was put into production in 1965.At present,it has enterd the ultra-high water cut stage.In general,it has the following features:(1)The production decline rate is fast,the annual oil production of the reservoir shows a trend of decreasing and the natural decline rate is large.(2)Heterogeneity is strong,no matter in the interlayer or on the plane,it has been seriously flooded.The remaining oil distribution is scattered and complex,and tap the latent resource is more and more difficult.(3)The development of well pattern and production method can not meet the requirements of development at the present stage,degree of water flooding control is low,well condition is getting worse,injection-production ratio of the existing well pattern is poor,formation pressure decreases rapidly.These factors seriously restrict the stable production of reservoir.Therefore,in order to ensure the stability even the increasement of the ST reservoir production,and realize the sustainable and stable development.The geological features must be reunderstood,master the production decline regularity of single well and block,and master the distribution of remaining oil in the ST reservoir.Then find the improved recovery method in the ultra-high water cut stage of the ST reservoir.This paper studies the structural feature,formation characteristic,horizon nature and reservoir feature of the ST reservoir.And rediscovered its geological features.Based on the definition of production decline rate,reservoir engineering method and filtration theory,the 8 factors which influence the decline of production are derived,and the main measures to slow down the production decline are put forward.By using 4 kinds of common production decline regularities,the production decline equation is established,and the recoverable reserves of each study well are predicted.By using 5 kinds of common production prediction modle to analyze the production data of the ST reservoir in production decline stage,the result shows that,it has best works when using the hyperbolic decline model and decay curve model to predict the annual oil production and cumulative oil production.Based on the results of geological research,the structural model and property model of the ST reservoir are established by using 3D geological modeling.As the result of reserve recalculation,the geological reserves of the model increased 43.4×104t when compared with the known geological reserves,and the relative error is about 3.87%.It shows that the quality of the established geological model is reliable.Based on the reservoir numerical simulation technology,the numerical simulation model of ST reservoir is established.Evaluating the quality of history fitting by numerical simulation,it shows that:The trend of regional stratum pressure analog value which following the change of development time,is in keeping with thetrend of actual stratum pressure which following the change of development time.The relative error of reserve fitting is 3.09%,the mean absolute error of composite water cut is 1.7%,the relative error of cumulative oil production is 2.7%,the relative error of cumulative liquid production is 0.4%.So the established numerical model is reliable.Based on this,the numerical simulation of remaining oil distribution is carried out from two aspects of reservoir vertical and horizontal.And according to the results of remaining oil distribution research,reasonable measures which can improve the recovery ratio are puts forward.Finally,the strategy of enhancing oil recovery in ST reservoir is deployed,and the future development indexs are forecasted.The prediction results of numerical simulation development index show that the liquid production rate increases 5.95%,the oil production rate increases 0.45%,the composite water cut decreases 1.1%,the cumulative oil production increases 24.43×104t,the recovery rate increases 4.14%,and the production decline rate decreases.Therefore,a good recovery effect is obtained,and a feasible potential tapping measure is indicated.