The Optimization Research Of Multiple-fracturing Wells Development In Low Permeability Reservoir

The low permeability reservoir has the characteristics of low porosity and low permeability.Most of it are glutenite or siltstone and widely distributed in China.It is difficult for conventional means(such as vertical wells and fracturing vertical wells)to improve the seepage environment of the developing low permeability reservoir that is a thin layer.Now in ChangQing oilfield and ShengLi oilfield,the technology that based on multiple fracturing horizontal well to development tight oil has been successfully used and becomes more and more mature.On the other hand,the thickness of some reservoir is very big and the vertical span is high.It need the unconventional multiple fracturing vertical well which will makes many fractures in the vertical direction to help develop.Studies have shown that low permeability reservoirs need to consider nonlinear flow concluding start-up pressure gradient and stress sensitivity.It will has exact influence on guiding reasonable fracturing parameters and production system.Multiple-fracturing development using elastic development way will face the problem of energy decrease quickly.Although water injection can supplement the energy,waterflood is easy to flow along the high permeability fracture.Therefore the paper is based on multiple-fracturing horizontal and vertical well technology and references for the practical production data of typical low permeability blocks in ShengLi oilfield.The seepage flow characteristic of the multiple fracturing horizontal and vertical well development is analysed.The paper optimizes fracturing parameters and confirm reasonable production pressure difference based on the research of capacity influence factors.The multiple-fracturing well model in low permeability reservoir is built to study the suitable water injection ways of multiple fracturing horizontal well and the fracture distribution of multiple fracturing vertical well.Seepage mathematical model of multiple fracturing horizontal well in low permeability reservoir is built considering special factors of dense reservoir(start-up pressure gradient,pressure sensitivity of matrix and flow conductivity of fractures).Solve the model to get the actual reservoir seepage characteristics and development laws and analyze the pressure,streamline,pressure gradient field.Then divide the seepage period and analyze production performance through the parameters such as daily oil,oil recovery index.By analyzing the influence on production capacity when fracture parameters changing to confirm the main control factors of production capacity and influence law.Then design reasonable production pressure difference based on the productivity index,seepage stage,the pressure coefficient by reservoir numerical simulation and reservoir engineering analysis method.On the other side,take multiple fracturing horizontal-drain as example to analyse the production law of elastic and water injection developmrnt.Aiming at the problems such as insufficient formation energy and water logging,study water injection&production and advanced water injection developmet ways based on the theory of imbibition.Compare the development effect and the production influence factors to ensure the development ways that can both complement formation energy in time and slow down the speed of water along the fractures.When the vertical thickness of low permeability glutenite reservoir is pretty large,the paper compares the development effects of the multi-branch horizontal well and the multiple fracturing vertical well;then the productivity influence factors such as the fracture diverting capacity,drainage area and formation permeability are analyzed;the plate of the length offractures,C_f/K_m(the ratio of fracture diverting capacity and formation permeability)and production is made for fracturing design optimization,and the paper studies the influence of rhythm and permeability range to the development;finally,the paper studied the fracturearranging principle including the length,height and spacing of fractures.