Investigation Of Reasonable Bottom-hole Pressure At Different Development Stages Of Tight Oil Reservoir In Block X

Unconventional tight oil and gas resources have shown great development potential.Development from unconventional tight oil and gas reservoirs is becoming a considerable support to ensure China's energy strategic security.There is no natural industrial production of tight oil reservoirs,and hydraulic fracturing technologies have been widely used to promote cost-effective development of unconventional and tight oil reservoirs.During the exploitation of tight oil reservoir,the problems of rapid formation pressure decline,rapid production decline and low recovery efficiency are accompanied.In order to make full use of formation energy and effectively control production decline,one of the common technical way is to optimize the reasonable bottom-hole pressure.In this paper an investigation on the determination of reasonable bottom-hole pressure at different development stages was conducted from the reservoir engineering perspective with the objective of maximizing production from tight oil reservoir in Block X:(1)the porosity and permeability parameters of the cores under different effective overburden pressure in tight oil reservoir of Block X were measured and the stress sensitivity of the tight reservoir was evaluated to be moderately strong to strong.The PVT measurement of formation crude oil in Block X was carried out to clarify the variation characteristics of high-pressure physical parameters of the reservoir fluid.The oil-water/oil-gas phase permeability curves were measured using the cores of tight oil reservoir in Block X.These experimental results provide basic data for the numerical simulation technology to determine the reasonable bottom-hole pressure at different development stages.(2)Based on the permeability variation characteristics of tight oil reservoir in Block X,three representative well areas were selected to study the variation of oil production with bottom-hole pressure at different development stages by numerical simulation method;The effects of dimensionless parameters such as highpressure physical properties of crude oil,fracturing fluid damage,formation stress sensitivity,fracturing fluid backflow and skin factor on single well productivity are defined.Properties such as crude oil viscosity,reservoir damage,and stress sensitivity show the most sensitive effects on the degree of single-well recovery.According to the analysis of numerical simulation results,when the formation pressure drops to 50%,the reasonable bottom-hole pressure changes less,so using 50% as the boundary,the development stages are divided into early development and late development,and the reasonable bottom-hole pressure curves for different development stages of reservoir with different permeability levels in Block X are drawn.(3)In this paper,based on the data of fluid level recovery monitoring and unstable well test of five tight oil wells in Block X,the evaluation of the application effect of the method of determination reasonable bottom-hole pressure was provided.The field application coincidence rate is 80%,which proves the feasibility of the reasonable bottom-hole pressure determination method proposed in this study.The results of this paper provides a scientific method for optimizing the reasonable bottom-hole pressure at different development stages of tight oil reservoir,and provides guidance for realizing the integration of tight oil reservoir-wellbore-surface to determine the reasonable bottom-hole pressure.