Historical modeling of gel filter cake recovery often predicts relatively fast gel recovery. A common method to slow gel recovery in simulations is to use yield point behavior for the gel filter cake. Recent measurements of concentrated, broken gel exhibited Carreau-type viscosity behavior that could mimic an apparent yield point. A new rheology model built on those measurements was used to upgrade a fracture cleanup and chemistry simulator (FCCS) to study potential cleanup mechanisms of gel filter cake during flowback of fracturing treatments.

Two cleanup mechanisms were explored with the FCCS. The first was a simple dilution mechanism in which the gel filter cake was immediately diluted as water re-entered the proppant pack from the matrix. The method used two-phase flow modeling and predicted excellent cleanup of delinked borate filter cakes and high concentrations of gelling agents in the return fluids—a prediction not observed in well returns. The second mechanism required development of three-phase relative permeability curves for water, gel filter cake, and gas phases in the proppant pack. The simulation studies using this mechanism only modeled displacement cleanup and predicted poor recovery as a result of a combination of filter cake rheology and relative permeability. This affirmed the poor apparent cleanup of some fracturing treatments, but underestimated return gelling agent concentration. The studies also demonstrated the role of gel phase saturation on gas productivity.

This work demonstrates that a proper choice of the operative three-phase relative permeability curves for water, gel filter cake, and gas is important for constraining the premature return of gel filter cake in cleanup simulators. Future laboratory work should consider the direct measurement of the three-phase relative permeability curves in proppant packs.

You can access this article if you purchase or spend a download.