Study On Depressure And Increasing Injection Technology For High Pressure Wells In Low Permeability Z Oilfield

Under the current situation of low international oil prices and high development costs,water injection development as a cheap and efficient development technology is still the first choice for most low-permeability oil fields.After years of water injection development in low-permeability oilfields,due to reservoir damage and other problems,the oil pressure of the water injection wells will rise,the injection volume will decrease,and injection will be difficult,forming the characteristics of"high pressure and under-injection"in the water injection wells,which will severely restrict the stable production of the oilfield.Under long-term high-pressure water injection conditions,the surface injection system and casing are working under high load conditions,which not only has the risk of damage,but also has low water injection efficiency.Under the current situation,combining geological factors and development factors,in-depth exploration of the causes of under-injection under high pressure in low-permeability oilfields,and formulating corresponding measures to reduce pressure and increase injection is an indispensable step to improve the energy efficiency of water injection wells.It is also an important link to improve the recovery in the middle and late stages of water flooding development.This article focuses on the two main development units of the low-permeability Z Oilfield,23-A and 25-C.Based on historical production data,we analyze high-pressure water injection wells.Combined with geological factors,the status of under-injection in high-pressure wells is clarified.Using laboratory experimental research methods,the reasons for high-pressure under-injection were analyzed from two aspects:the compatibility of formation fluid and injected water and the evaluation of reservoir sensitivity.Based on the experimental determination of the starting pressure gradient,a distribution model of pressure drop funnel considering the starting pressure gradient is deduced,and the factor of pressure drop funnel is studied from two aspects:single factor and multiple factors.Based on the above analysis,a non-linear numerical simulator was used to establish a numerical characteristic model of the Z Oilfield considering the starting pressure gradient,and to carry out the optimization of the pressure reduction and injection increase program.The research results show that the proportions of under-injection wells in the two main development units of the low-permeability Z Oilfield are 39%and 42%,respectively,with severe high pressure and under-injection characteristics.The water injection wells with high oil pressure in the early stage are located at the edge of the sand body with poorly developed reservoirs,and the water injection wells with high oil pressure in the later stage mainly have serious scaling due to the poor compatibility of injected water and formation water.The start-up pressure gradient of Z Oilfield is 0.0035-0.0584 MPa·m^-1.The start-up pressure gradient will cause more pressure loss between the injection and production wells,requiring greater injection pressure to establish effective displacement,and the skin factor has the greatest influence on the pressure distribution between the wells.The incompatibility of fluids and the presence of a starting pressure gradient in the reservoir are the root causes of high pressure and under-injection in water injection wells.From the perspective of improving compatibility,eliminating near-well blockage,and reducing pressure consumption between wells,a treatment technology of strict control of injected water quality+acidification+surfactant flooding is proposed.Through numerical simulation,the optimal value of surfactant injection concentration is 1%,the optimal value of slug size is 0.2 PV,and the optimal value of injection-production ratio is 0.9.The non-linear numerical simulator was used to simulate the development of the scheme for 15 years,and the recovery degree was increased by 3.19%compared with the water drive.For different types of under-injection wells,different treatment schemes are given.Field application results show that on the basis of control of water quality strictly,combined with measures of acidification and surfactant flooding is effective and can be promoted and applied in other high-pressure and under-injection wells in the Z Oilfield.