Study On Comprehensive Adjustment Method Of Secondary Return Layer In Tertiary Oil Recovery In X And Y Blocks

The injection of P?5?P?10 reservoir in ASP flooding in Block X stopped in June2019.At present,the average daily oil production of single well is 0.7t,and the comprehensive water cut is 97%.The injection of S?10?S?10 reservoir in ASP flooding in Block Y stopped in 2020,with an average daily oil production of 1.9t and a comprehensive water cut of 95.6%.The two blocks are geographically adjacent,and both are in the subsequent water drive stage of ASP flooding,and the water cut rises rapidly.On the basis of detailed reservoir description,this paper studies the development status of oil layer,analyzes the production status of oil layer,compares the productivity construction and economic benefits brought by different return layers and return time,and determines the adjustment potential of ASP flooding in oil layer.This paper mainly discusses the timing of secondary upward(downward)return of tertiary oil recovery and the selection of layers,and optimizes the design for weak alkali ASP flooding development.Finally,it is determined to use the existing tertiary production well network to return to S?1-9 oil layer and drive with water.By analyzing the adaptability of ternary composite system to formation and comparing with the development experience of other blocks,it is finally determined that the system formula adopts weak alkali system,the surfactant is petroleum sulfonate,the alkali is sodium carbonate(heavy soda ash),and the polymer molecular weight is designed according to 12-16 million and 16-19 million,so as to meet the actual production demand.The slug design adopts the combination mode of 0.05PV preposed polymer slug+0.35PV ASP flooding main slug+0.15PV ASP flooding auxiliary slug+0.25PV subsequent protection slug.It is predicted that ASP flooding in S?1-9 reservoir will be put into production in October 2021,with a built-up production capacity of 12.6×104t,and chemical flooding development will start in June 2022,reaching the peak of effectiveness in 2024,with a built-up production capacity of 35.0×10~4t at the peak,after which the output will start to decrease and the water cut will rise,with an average annual oil production of 25.4×10~4t at the stage of chemical flooding.According to the economic benefit evaluation,with 10 years as the evaluation period,after deducting relevant sharing expenses,the after-tax financial internal rate of return is 8.5%,the financial net present value is 196.392 million yuan,and the investment payback period is 7.1 years.The project is economically feasible.