Geological Control Factors Of Brittleness And Hydro-fracturing Potential Evaluation Of Shale Reservoir In DX Block,Southeastern Sichuan

The characteristics of low porosity and low permeability of shale reservoir determine the need of fracturing for shale gas commercial exploitation.There are many factors that affect the reformability of shale reservoir,among which shale brittleness directly affects the development of fracture network formed after the formation is compressed.Therefore,it is very important to study the brittleness of shale reservoir.Based on the characteristics of shale reservoir in Wufeng-Longmaxi Formation in DX block,the first explore the geological controlling factors of brittle shale reservoirs and the relationship between various factors,and then through the method of numerical simulation analysis of hydraulic fracturing cracks expanded shale reservoirs,finally combined with the fuzzy comprehensive evaluation method,shale reservoir can be modified evaluation model is established,and the reliability evaluation model is validated by an engineering example.The following conclusions were drawn:(1)The shale in DX block contains the highest contents of quartz and clay minerals,followed by carbonate and feldspar;With the increase of the test confining pressure,its elastic modulus and compressive strength all increased to a certain extent.The porosity and permeability of shale are poor.The micro pores are mainly mineral pores and organic pores,and the porosity and permeability are poor.(2)An increase in quartz content will also result in an increase in brittleness,while that of clay minerals weakens the brittleness of shale.The higher Young's modulus is,the brittleness has a positive correlation.The change of brittleness and Poisson's ratio is negatively correlated.The increase of temperature and confining pressure in deep shale reservoir will lead to the rise of peak strength,the increase of peak strain and the weakening of brittleness.The difference coefficient of in-situ stress affects the fracture mode of rock mass and the extension and penetration of fractures in rock mass,thus affecting the brittleness of shale.(3)The mineral composition of shale reservoir affects its macroscopic mechanical properties:the increase of quartz mineral content is helpful to improve the Young's modulus of rock mass,while the clay mineral will weaken the mechanical properties of rock mass,resulting in the decrease of Young's modulus.(4)The fracture length increases with Young's modulus increasing;The high brittleness shale reservoir has a long fracture extension distance and good reformability.The decrease of the minimum horizontal principal stress is helpful to increase the fracture length.The size of permeability directly controls the fracture development in the formation.The larger the permeability is,the longer the fracture length is and the better the compressibility is.The higher the fracture toughness,the more difficult the fracture is to form and the lower the fracture elongation length.(5)The evaluation model of shale reservoir reformability was established,and it was found that the overall reformability of the shale section of Wufeng-Longmaxi Formation was good,and the evaluation model was in good agreement with the field fracturing construction results.Figure[43]Table[17]Reference[87]...