Hydrofluoric Acid Reaction With Sandstone Formations

Abstract

A mixture of hydrofluoric (HF) and hydrochloric (HCl) acids is often used to stimulate gas and oil production from sandstone reservoirs by increasing formation porosity and permeability near the well bore. This acid mixture is used since it will react with almost all constituents of naturally occurring sandstones and solids used in drilling and workover fluids. The penetration of hydrofluoric acid into the formation is primarily controlled by the chemical composition of the minerals which acid contacts. Smith and Hendrickson and Gatewood have shown that the reaction rate of hydrofluoric acid with calcite or silicate minerals (clay or feldspar), for example, is much more rapid than with silica. Therefore, if large quantities of the highly reactive minerals are contacted, acid will not penetrate deeply into the formation. In this test, acid was injected into a linear core and the permeability measured as a function of acid throughput. The acid volume required to attain a desired permeability increase divided by the core cross-sectional area was then used to design the treatment. Farley et al. reported similar test data taken in automated experimental equipment. This test procedure gives useful information regarding acid reaction with sandstone; however, its use as a design proceduremore » is limited.« less