Rock Mechanics And Evaluation Of Fractability Of Chang 7 Tight Sandstone Reservoir In Heshuin Area,Ordos Basin

The Heshui area is rich in crude oil resources and is an important reserve block for increasing oil reserves and production of Changqing oilfiled.However,the tight sandstone reservoirs of Chang 7 member in study area is influenced by deep-water gravity flow sedimentation and is highly inhomogeneous,and there are problems such as unsatisfactory fracturability evalution using single brittleness index,which has caused trouble in the selection of well and strata for fracturing.In view of the above considerations,this paper is guided by the theories of sedimentary petrology,petroleum geology,logging geology and rock mechanics and based on the basic geological characteristics,combined with rock mechanics experiments and well logging data and statistical analysis methods to establish a quantitative fracturability evaluation model for the tight sandstone reservoirs in Heshui area.The fracturability evaluation of tight sandstone reservoirs of Chang 7 member in Heshui area was carried out.The following findings were made:First of all,based on a variety of geological data and test data,the characteristics of tight sandstone reservoirs of Chang 7 member in Heshui area are systematically studied.The result shows that the sandstone reservoirs in study area is mainly a deep-water gravity-flow sedimentary sand body.The physical properties reservoirs are poor and characterized by super-low-urtal-low porosity and ultra-low permeability.The pore types of the reservoir are dominated by feldspathic pores and residual intergranular pores,and submicron pore is the main body of the reservoir storage space in study area and with complex pore structure;the sandstone reservoirs in study area mostly develope high-angle tectonic fractures,and the average linear density of the natural fractures is 0.13 strip/m;the coupling relationship between natural fractures and in-situ stress is high,which is conducive to the fracturing and transformation of the reservoir.Secondly,based on the results of rock mechanics tests,the rock mechanics characteristics of the tight sandstone reservoirs of Chang 7 member were understood,and the effects of peritectic pressure,depth,lithology and physical properties on rock mechanics parameters are analyzed.The results of imaging logging,wave velocity anisotropy,and underground microseismic monitoring show that the maximum horizontal principal stress of Chang 7 member spreads along the NEE-SWW direction,and the acoustic emission test shows that the magnitude of in-situ stress of Chang 7 member is consistent with the positive fracture mechanism ofσ_v>σ_H>σ_h and the horizontal in-situ stress difference is moderate.In addition,based on logging data with multiple regression method,a basic model is established to predict transverse wave time data,and a rock mechanics logging characterisation study was carried out based on actual test data and logging data.Finally,based on the analysis of the influencing factors of reservoirs fracturability,five indexes such as brittleness index,fracture toughness and horizontal in-situ stress difference were selected,and a fracturability evaluation model was established by combining the analytic hierarchy method to evaluate the fracturability of tight sandstone reservoirs in study area,and the reliability of the fracturability evaluation model was verified through on-site fracturing data,post-compression oil test analysis and microseismic monitoring data.The results of study provides a certain reference for the evaluation of the fracturability of tight sandstone reservoirs of Chang7 member in Heshui area.