New Fracture-Acid Technique Provides Efficient Stimulation Of Massive Carbonate Sections
Authors: Hendrickson A.R. , Cameron R.C. 
Published: March 2010

ABSTRACT
A new stimulation technique has been developed and successfully applied todeep massive carbonate completions in several areas. This same technique shouldprove useful in similar massive carbonate sections in Canada. Basically, thenew technique provides deep fracture penetration into the reservoir withlow-cost fluids and good fracture conductivity by effectively etching thefracture faces with special acid formulations.
It differs from conventional hydraulic fracturing treatment only in thatacid replaces conventional propping agents. The treatment is economical in thatit uses inexpensive frac fluids to create fracture area and penetration andreduce fluid leak-off. Much smaller quantities of acid may then be used to etchthe desired conductivity at the required depth of penetration in the reservoir.If acid alone were used, the volume required would be prohibitively expensive.
The new technique also eliminates many of the hazards of conventionalfracturing and acidizing. As no propping agent is used, there is no danger ofscreen-outs. Corrosion is minimized, because the pad volume of frac fluid coolsthe well equipment prior to the injection of acid. The technique, thus, is particularly useful in deep, high- temperature reservoirs.

INTRODUCTION
MASSIVE low-porosity, low-permeability carbonate formations such as the Ellenburger, Devonian, Hunton, Edwards, Budda and Smackover in the United States, and the Mississippian in Canada, are known to contain substantial andattractive quantities of hydro-carbons. Many of these accumulations have notresponded sufficiently to conventional stimulation techniques to warrantfurther exploration. Although a two-to three-fold productivity improvement canfrequently mean the difference between a noncommercial and commercial well, conventional acidizing and/or fracturing treatments have not provided suchincreases for sustained periods. A new dual fracturing-acidizing stimulationtechnique is now showing promise of improving productivity from these massiveformations.
Basically the new fracturing technique provides deep reservoir penetrationwith low-cost fluids and good conductivity by effectively etching the fracturefaces with acid. Thus, it utilizes the advantages of both fracturing andacidizing penetration of the reservoir by the hydraulic fluids and developmentof high conductivity by acid. This treating technique also minimizes theprincipal hazards of conventional fracturing and acidizing-screen-outs andcorrosion. The combination also provides a more effective and economicalapproach to stimulation with acid-based fracturing fluids.
Massive carbonates are often characterized by their extreme thickness anddepth, with accompanying high pressure and temperature. They often have extremelow permeability, and porosity. The permeability that is present is often inthe form of a fine interlacing of natural fractures and, in some cases, vugularsystems. Very little, if any, true matrix permeability exists. These primarycharacteristics have led to the difficulty in efficient, and effectivetreatment for stimulation.
The thickness of these formations may range as high as several hundred feet, with depths of up to 25,000 feet. Thus, the low porosity dictates that theentire vertical extent of the formation must produce if ultimate recovery is tobe commercially attractive. Low permeability dictates that desired conductivitymust penetrate deeply into the reservoir to obtain commercial recoveryrates.
THE PAPER WAS PRESENTED: at the 19th Annual Technical Meeting of The Petroleum Society of CIM, Calgary, May, 1968. Technology, January-March, 1969, Montreal Canada