Optimization Of Hydraulic Fracturing Operation Parameters Considering Dynamic Filtration Coefficient

Unconventional oil and gas reservoirs in China are characterized by low porosity,poor permeability and difficult exploitation,which seriously restrict the development of unconventional oil and gas resources in China.Hydraulic fracturing is to improve oil and gas production by injecting fracturing fluid into the wellbore continuously to make the rock fracture and produce fractures and improve reservoir permeability.Therefore,the key to optimize the parameters of hydraulic fracturing is to study the fracture extension law in the process of hydraulic fracturing.In view of this,this paper uses the method of combining theoretical research and numerical simulation to carry out a series of Optimization Research on hydraulic fracturing operation parameters of vertical wells and horizontal wells.Considering the stress sensitivity of rock in the process of hydraulic fracturing,based on the principle of effective stress,the model of dynamic permeability and porosity of reservoir was established;further considering the influence of dynamic changes of permeability and porosity on the filtration of fracturing fluid,the model of dynamic filtration coefficient of fracturing fluid was established.Taking the experimental data of coal and rock in Jiaozuo mining area as the basic parameters,the theoretical model was embedded in ABAQUS software by using FORTRAN language,and the hydraulic fracturing numerical model of vertical well was established.The influence of different fracturing fluid displacement and viscosity on fracture propagation and extension law was deeply discussed,and the results were compared with the measured results of microseismic.The results show that: in the process of hydraulic fracturing,under the condition of surface equipment permission,the fracturing fluid with large displacement and low viscosity should be selected as the prepositive fluid to make fractures,and then the sand carrying fluid with large displacement and high viscosity should be replaced to support fractures,which can not only improve the sand carrying capacity,but also ensure the fracturing volume and enhance the fracturing effect.The fracturing time is 40 ? 60 min,and the fracture extension length is 87.5 ? 112.0m,which is consistent with the results of microseismic measurement(82.4 ? 109.5m)in the mining area,thus verifying the correctness of the results.According to the data of test wells in Changji oil and gas field,a numerical model of staged fracturing of horizontal wells was established based on the same principle.The process of synchronous hydraulic fracturing and sequential hydraulic fracturing under different perforation spacing was simulated,and the fracture distribution and extension law under different working conditions were discussed.The results show that: For synchronous hydraulic fracturing of horizontal wells,when the perforation spacing is 95 ? 100 m,the fracture shape is relatively simple,all fractures extend along the direction of the maximum horizontal principal stress,and the average height of fractures basically does not change,so the fracturing effect is the best.For the sequential hydraulic fracturing of horizontal wells,when the perforation spacing is 70 ? 75 m,the average height of each fracture is basically the same,there is no height difference between fractures,and the fracturing effect is the best.The simulation results of sequential fracturing of horizontal wells are consistent with the perforation spacing(75.3m)of sequential fracturing of horizontal wells in the study area,which verifies the correctness of the simulation results.The research results can provide solid technical support for the development of similar projects at home and abroad.