Research On The Flow Conductivity Of Shale With Inclined Propped Fractures In Northwestern Hunan

Hydraulic fracturing is required in shale gas exploitation,and the propped fractures are an important factor affecting the final gas production of shale gas wells.Due to the irregular and uneven distribution of shale joints and weak surfaces,inclined fractures with different angles will be generated during hydraulic fracturing,and these propped fractures have different conductivity characteristics.Using the self-developed low-permeability reservoir sand-carrying and fracture expansion system and prefabricated fractured shale,single-fracture conductivity tests under different dip angles are carried out to study the evolution law of tilt fracture conductivity under the action of proppant.The results showed that:(1)Through the physical and mechanical properties experiments of fresh black shale outcrops in northwestern Hunan,it is found that the shale in this area has higher compressive strength,shear strength and fracture toughness,and lower Poisson’s ratio and Young’s modulus,indicating that the shale texture in this area is compact and has high strength and brittleness.(2)Experiments on proppants with different particle sizes and types found that the larger the particle size of the proppant within a certain size range,the greater the porosity after the fracture is squeezed by the closing pressure,and the stronger the conductivity.The strength of ceramsite proppant is greater than that of quartz proppant,and the porosity of propped fractures and the fracture rate of proppant are lower,which is conducive to maintaining the conductivity of propped fractures.For this reason,this test mainly uses 20/40 mesh ceramsite proppant for the test.(3)The larger the inclination angle of shale fractures,the weaker the conductivity,and the conductivity of straight fractures is 11.4-25.6%higher than that of inclined fractures.Under the same closing pressure,the porosity of fractures with different dip angles is equal,but the closing displacement of fractures with high dip angles is larger.The migration ability of proppant in proppant fractures increases with the increase of angle,and proppant with large particle size in inclined fractures is more likely to remain and play a supporting role.(4)The propped fractures after the diversion test are analyzed by the three-dimensional topography scanning system,and the embedding law of proppant in fractures with different inclination angles is obtained.The results show that the larger the fracture inclination angle,the lower the embedding depth of proppant,and the lower the embedding depth of proppant.Therefore,there are obvious differences in the roughness of the fracture surface with different inclination angles.The roughness of the fracture surface is analyzed by using the JRC value and fractal dimension.It is found that the larger the inclination angle of the fractures,the smaller the JRC value.The fractal dimension also shows a decreasing trend with the increase of the dip angle,indicating that the fractures with dip angle are more uniform with depth distribution and flatter than the straight fractures after being embedded by proppant.(5)Based on the Hertzian contact theory combined with the experimental parameters and data,the empirical calculation formulas of proppant and embedded depth under different fracture dip angles are obtained.According to the change characteristics of roughness and the correlation of parameters,the roughness calculation formula of fracture surface under different closing pressures and dip angles is obtained.Then,based on the fracture conductivity corresponding to different roughness,the conductivity calculation model is improved,and a new conductivity calculation model considering the dip angle is obtained,and the model calculation data is compared with the test data.It is found that the two have a good degree of agreement,and the calculation model is feasible.