A New Dimensionless Approach to Assess Relative Permeability Modifiers

Water production is one of the common problems that is faced in mature gas reservoirs. A number of methods exist to tackle this problem, including injecting polymer that can selectively reduce water production. There are many factors that affect this treatment, such as rock permeability and porosity, flowing fluid phases, polymer concentration, and the dependency of polymer thickness on the flow rate of each phase. In this manuscript, we propose a dimensionless form of the effective pore radius (r(eff)(-)) that can be used to evaluate the effectiveness of such a treatment. This form takes into account the thickness of the absorbed polymer layer onto the pore surfaces of the rock, which is an important factor controlling the performance of the treatment. Our newly developed r(eff)(-) explicitly demonstrates the effects of the above factors by considering them during its calculation. This manuscript also demonstrates the application of r(eff)(-) in analyzing the outcome of a number of experiments conducted in this work. With regard to the gas phase, our experiments show that at low flow rates (0.2-1 cm(3)/min) as the polymer concentration increases from 1000 to 8000 ppm, r(eff)(-)decreases and is less than unity for concentrations of 1000-4000 pppm, indicating improved post-treatment permeability to gas. When the gas flow rate is increased to 2 cm(3)/min and beyond, the r(eff)(-) is almost equal to one across all polymer concentrations. This is attributed to the polymer layer losing its effects on flow behavior due to possible increasing polymer rigidity caused by increasing shear rate. With regards to the water phase, although r(eff)(-) follows a different trend against polymer concentration than that of gas, it remains less than one across all concentrations used, indicating the desirable reduction in post-treatment permeability to the water phase. Further analysis on the experimental results using the Forchheimer equation reveals the presence of three flow regimes with increasing gas flow rate.