Quantitative prediction of fracturing fluid leak-off in shale gas reservoirs based on spontaneous imbibition model of fracturing fluid
Hydraulic fracturing is often used for the development of unconventional oil and gas resources to improve the production rate of single well.However,the field data of fracturing indicate that a large amount of fracturing fluid retains in the strata,which results in a lower flowback rate of fracturing fluid and may have some impact on underground reservoirs and groundwater environments.In order to further study the leak-off mechanism of fracturing fluid and accurately predict the amount of fracturing fluid leak-off,this paper establishes a model describing the spontaneous imbibition of fracturing fluid caused by capillary force.Then,the amount of fracturing fluid leak-off is quantitatively calculated,and verified using the field data.Finally,the dimensionless imbibition rate parameter is introduced to analyze the key factors controlling fracturing fluid loss.And the following research results are obtained.First,during the fracturing construction of a horizontal well in shale gas reservoirs,about 50%-95%of the fracturing fluid is imbibed through the matrix.The amount of imbibed fracturing fluid is only related to imbibition rate parameters,fracture areas and imbibition time.Second,when the ratio of wetted phase viscosity to non-wetted phase viscosity exceeds the threshold,the imbibition rate parameter is mainly dependent on the pore size distribution parameter of the rock,while the effect of fluid viscosity is very limited.Third,when the pore size distribution parameter is between 0.5 and 0.7,imbibition rate parameter reaches a higher value,i.e.,more fracturing fluid is imbibed into the strata.Fourth,when the ratio of wetted phase viscosity to non-wetted phase viscosity exceeds 10 and the pore size distribution parameter is less than 0.8,the optimized spontaneous imbibition model has greater applicability.In conclusion,the spontaneous imbibition model of fracturing fluid established in this paper can accurately predict the amount of fracturing fluid leak-off,and provides a technical support for the production of unconventional oil and gas and the environmental protection.
Shale gas reservoirCapillary forceLeak-offSpontaneous imbibitionImbibition rate parameterFluid viscosityPore size distribution parameter
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