Paper: Steve Metcalf, BJ Services Co.

Fracture acidizing of carbonates has yielded increases in production in many areas. But depending upon the rock strength and the reservoir closure pressure this may be lower than expected. Also, as a result of closure and rock strength, production may decline at a higher rate than after a proppant fracture treatment. Laboratory results are presented describing the effect on the strength (Softening) of a dolomite and limestone after exposure to various acid systems. A dolomite saturated with potassium chloride water exposed to neat, emulsified, gelled and crosslinked 15wt% hydrochloric exhibited strength improvements going from neat to one of the fluid loss controlled systems by approximately 70%. A limestone tested similarly showed approximately 100% strength improvement. Tests were also performed on the rocks in a dry state and saturated with synthetic oil. These tests also had marked improvements in from 25 to over 100%. Treatments using an increased volume of acid systems with lower matrix leak-off should provide longer-term production responses.