Colmatation of reservair rocks in the operation of oil fields as a result of cation exchange

Abstract

By analyzing the changes in seawater pumped to maintain reservoir pressure (FPD), the anhydrous granitoid reservoir of the White Tiger deposit, in which the cracks are partially filled with calcium minerals (calcite and lomontite), shows that these minerals interact with the injected seawater. Hydrogeochemical modeling of this process showed that cations of seawater are first sodium and then magnesium displace calcium from the lomonite exchange complex, which leads to precipitation of anhydrite and a small amount of calcite. The incoming water dissolves the anhydrite and precipitates it downstream, forming a gradually expanding annular region with a constant increase in the amount of precipitated anhydrite. As a result, there is a decrease in the permeability of the fracture medium due to the filling of the cracks with anhydrite. A large amount of calcium in the associated waters when they rise to the surface causes the precipitation of calcite in the production wells and surface equipment. The transition of drilling to ever greater depths, where the rocks contain lomontite almost everywhere, requires taking into account the phenomena of cation exchange between the injected water and the rock in the predictions of scaling.