THE POTENTIAL OF HYDROCARBONS TO AFFECT THE ABILITY OF KCL TO STABILIZE MONTMORILLONITE

Clay swelling is a potential problem in oil and gas reservoirs because swelling clays impede the flow of hydrocarbons. One strategy to mitigate clay swelling is to introduce KCl into the formation, but the effect of hydrocarbons on clay stabilization is not well understood. We conducted experiments to evaluate interactions among swelling clays, KCl, and hydrocarbons. Wyoming Na-rich montmorillonite (SWy-2) + formation water ± hydrocarbons were combined with two different quantities of KCl. The resulting solution contains 0.4 and 2.2 mol/kg KCl, concentrations spanning the range of KCl used in field applications. The formation water (pH = 1.83 and ionic strength = 0.015) contains mmol/kg quantities of Na and Cl and <1 mmol/kg K, Ca and Mg. The formation water is modeled after surface water used as a makeup fluid for hydraulic fracturing operations and the hydrocarbons are oil extracted from a Cretaceous sandstone in the Powder River Basin, Wyoming. All four experiments reacted at 30°C for at least 28 days. K concentrations decrease and Na concentrations increase in formation water in all four experiments, suggesting that K exchanges with Na in the clay. XRD results suggest that montmorillinite swelling is not reduced in the experiment containing 0.4 mol/kg KCl. Thus hydrocarbons appear to inhibit the effectiveness of low amounts of KCl (0.4 mol/kg) to stabilize clays whereas the presence of hydrocarbons appear to have no effect on high amounts of KCl (2.2 mol/kg).