The first observation and description of hydraulic fracturing, by Grebe and Stoesser (1935), involved injecting acid to stimulate oil production from a carbonate formation. With the advent of hydraulic propped fracturing of sandstones with oil and sand in the late 1940s, fracture acidizing has been generally confined to carbonate formations; its advancement did not match that of propped fracturing. By the 1970s, propped fracturing of carbonates (in addition to sandstones) gained popularity through the greater understanding and ease of modeling fracture stimulation with non-reactive (non-acid) fluids. After the 1970s, however, advancements occurred in modeling fracture acidizing and in fracture acidizing stimulation theory. Thus, entering the 1980s and into the 1990s, fracture acidizing in carbonates increased, with development of a variety of fluid systems and multi-step procedures that are still in use today. Nevertheless, fracture acidizing continues as the less-preferred alternative to propped hydraulic fracturing in carbonates - and it has never been seriously considered as a stimulation method for sandstones.

With approximately 70% of worldwide hydrocarbon reserves in carbonate formations, and the need to simplify sandstone stimulation treatments in general, the merits of fracture acidizing and its greater possibilities - for both carbonates and sandstones - must be considered.

This paper endeavors to briefly review the historical milestones leading to fracture acidizing, and their bearing on present methods and on the imposed rules. The paper touches on the types, purposes, benefits and limitations of present technologies and methods with a focus on the propped fracturing versus fracturing acidizing decision - and with a view to future possibilities and opportunities.

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