Modeling Fracture Fluid Cleanup in Hydraulic Fractures

Abstract

Abstract The retention of fracturing fluid in a proppant pack reduces the dimensionless fracture conductivity, Fcd, resulting in poor well productivity regardless of fluid type (gelled oil, crosslinked polymers, viscoelastic surfactants, or foams). Analytical expressions derived in this paper can be used to calculate the extent of fracture clean up, n* under a set of production conditions. Dimensionless parameters, β (reservoir: fracture mobility ratio), R (clean: fouled fracture permeability ratio), and τ0 (dimensionless fluid yield stress), which affect n* are identified in the model. A second fracture cleanup model is also proposed and is used to estimate the dimensionless parameter values. Fluid removal is a balance between the differential pressure within the fracture facilitating cleanup and the fluid yield stress resisting cleanup. The driving force for fracture cleanup weakens as fluid is removed, until an equilibrium cleanup extent, n*, is reached. The equilibrium model predicts that n* increases greatly with decreasing dimensionless yield stress, τo. The magnitude of η* is also greater for high clean: fouled permeability ratios, R. η* is expected to increase with an increase in the reservoir: fracture mobility ratio, β, until an optimum is reached and then decrease with increasing β. The critical process of parameter estimation is achieved by making experimental measurements and by history matching published fracture flowback data using the transient model. Practical application of this work is aimed at identifying pathways to improved well performance. For example, data from the Codell formation showed that η* was 45%. Parameter values of 0.92, 2.0, and 5.0 for τo, β, and R, respectively were found to fit the transient flowback data. If these parameters are accurate, η*, can be increased to 95% (doubling the expected production revenue) if a fluid with τo of 0.1 is used and all other parameters remain the same.