Study On Waterflood Development Behaviour And Remaining Oil Distribution Of Small Well Pattern In Wunan Oilfield

Wunan Oilfield is a typical low-permeability oilfield.Because the oil and gas distribution has the characteristics of “thin,multi,scattered and miscellaneous”,it is very difficult to develop waterflooding in Wunan Oilfield.In 2012,the well pattern thickening was carried out in Wunan Oilfield,and the water injection response was improved.However,due to the short adjustment time of the well pattern and the unclear understanding of the law,it is necessary to further study the water injection after the well pattern thickening.The current distribution of remaining oil in Wunan Oilfield is unclear,which brings certain difficulties for the adjustment of production in the later stage.Therefore,it is necessary to study the injection behaviour and residual oil distribution law of small well pattern in Wunan Oilfield.Based on the study of the reservoir geological characteristics of Wunan Oilfield and the statistical production data of 336 wells,this paper studies the development history of the three blocks of Wu 101,Wu 5 and Wu 4 in Wunan Oilfield and the waterflood response of 12 injection well groups by using the reservoir engineering method.The factors affecting the waterflood response were analyzed.Taking Wu 5block as an example,the waterflood advantage of small well pattern was studied from the aspects of production decline law and ultimate recovery factor before and after well pattern thickening.After the well network thickening,the production decline rate is reduced,and the ultimate recovery factor calculated by the empirical formula method,the corrected Tong's plate method and the water drive curve method is improved.The depth of plunger,working fluid level,water content,midpoint of pay zone and other data were used to calculate the bottom hole flowing pressure.The IPR curves of 113 wells were plotted to study the IPR curve type and formation pressure changes.In addition,the effect of stimulation treatment such as the perforations adding,fracturing and water plugging was studied over the years.Based on the geological and production data of Wunan Oilfield,the numerical simulation method was used to study the distribution of remaining oil in each small layer of Wunan Oilfield and the producing reserves of each oil group,to find out the areas with high remaining oil saturation,and to analyze the distribution of remaining oil.Finally,with the goal of increasing deliverability,the reservoir engineering method and numerical simulation method were applied to study the injection-production parameters such as the ratio of reasonable injection-production wells,production well bottom hole flowing pressure,injection well pressure,pressure maintenance level,injection-production ratio,etc.,the measures provide a basis for subsequent development adjustment measures.