Using screening test results to predict the effective viscosity of swollen superabsorbent polymer particles extrusion through an open fracture

Superabsorbent polymer particles, also called preformed particle gels (PPGs), have been successfully applied to reduce water production and enhance oil production in mature reservoirs with fractures or super-high-permeability streaks/channels. The applied particles usually range in size from a few hundred micrometers to a few millimeters and are irregular in shape, which make it impossible to measure their rheology behavior using a traditional rheometer. A simple method, a screen model test, was designed to evaluate the rheological behavior of the swollen PPG. The results show that a swollen PPG is a shear-thinning material with properties that can be expressed using a power-law equation from which an apparent consistency constant and an apparent flow index can be obtained. Considering the shear-thinning properties, we first developed a theoretical mathematical model using a general power-law equation to predict the pressure gradient of a swollen PPG during its extrusion through a fracture. Then, we modified the model by correlating screen test results with fracture experiment results so that the apparent consistency constant and the apparent flow index obtained from the screen tests were introduced to replace the consistency constant and flow index from the general power-law equation. These equations correlated effective viscosity with flow rate, fracture width, apparent consistency constant, and apparent flow index together. The newly developed correlations were validated, and the results showed that a single group of screen test measurements can be applied to determine the effective viscosity of a PPG in a fracture with limited errors.