Research On The Evaluation And Influence Factors Of Tight Sandstone Reservoir Fracability

Fracrability evaluation is the basis of the optimization of fracturing level and the evaluation of productivity after fracturing.The tight sandstone reservoirs in block 4 in central Junggar Basin are buried deep and poor in physical property,and it is urgent to improve the industrial productivity by fracturing.Therefore,on the basis of the previous research results,the fracture property of the Jurassic tight sandstone of Dong 2 well north area is studied as an example.Based on the experimental data of rock triaxial test,the fitting formula of fracture energy density and elastic modulus of tight sandstone is established.The fracture development index of different depths is determined by the criterion of rock fracture.The effect of different factors on the fracability is determined by numerical simulation.Fracture energy density is used to characterize the fracture toughness of tight sandstone,and the fracture development index is used to characterize the development degree of natural fractures.Considering the influence of rock brittleness,fracture toughness,in-situ stress and development degree of natural fractures,the weight of each parameter is calculated by analytic hierarchy process,and a new quantitative fracrability evaluation of deep and tight sandstone reservoirs is established.On this basis,combined with the distribution of effective reservoirs,fracturing horizon optimization is carried out.The feasibility of the method is verified by microseismic observation of D8 well fracturing,which provides technical support for further exploration and development in the study area.The main conclusions of the study are as follows:?1?The rock types are mainly siltstone,fine sandstone and argillaceous sandstone.The pore of rock is more developed,most of which are primary intergranular pores and dissolved pores,and the connectivity is good.Porosity is mainly distributed in 5¹0%,and permeability is mainly distributed in 0.1¹0mD.Most of the reservoirs are low porosity and ultra low permeability reservoirs.?2?The rock brittleness index of the study area is 0.50⁰.83,and the rock brittleness is better.The fracture energy density is mostly 83.5²75.4N·mm·mm^-3,and the energy required for crack propagation is larger.The horizontal stress difference coefficient ranges from0.17⁰.23,which is conducive to the formation of fracture network.The fracture growth index is mainly concentrated in 0.4⁰.8,and the reservoirs are mostly slightly developed fractures.?3?Numerical simulation analysis:The higher the modulus of the rock,the smaller the width of the crack and the longer the length of the crack.Poisson's ratio and ground stress environment have little influence on fractured fracture morphology.When the horizontal stress difference coefficient is large,the fractured fracture is easier to spread through the natural crack and continue to extend along the direction of the maximum horizontal principal stress with considering the natural cracks.On the other hand,natural cracks can easily induce the change of fracture crack direction,which first extends along the direction of natural fracture.?4?The lower of porosity limits of Toutunhe and Sangonghe formation are 4.5%,4.0%and the lower of permeability limits are 0.15mD,0.12mD.According to the size of the fracturing index,the reservoir can be divided into three types:when the FI is greater than0.55,the reservoir can be fractured well,and when the FI is between 0.50⁰.55,the fractured reservoir is moderate,and when the FI is less than 0.50,the fractured reservoir is poor.Furthermore,9 fracturing horizons of well D7,well D8 and well D701 are selected.