Colmatage of Reservoir Rocks in Oil Field Exploitation as a Result of Cation Exchange

The study of the change in the composition of the seawater injected for reservoir pressure maintenance (RPM) to the anhydrous granitoid reservoir of the White Tiger oil field, in which the cracks are partially filled with calcium minerals (calcite and laumontite), has shown that these minerals interact with injected seawater. Hydrogeochemical modeling of this process has revealed that the seawater cations (first sodium and then magnesium) displace calcium from the laumontite 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 fractured medium due to the anhydrite filling of the cracks. A large amount of calcium in the produced waters upon their rise to the surface causes the calcite precipitation in the production wells and the surface equipment. The transition of drilling to greater depth, where the rocks contain laumontite almost everywhere, requires considering the phenomena of cation exchange between the injected water and the rock in the predictions of scaling.