Alternate Stages of Pad Fluid and Acid Provide Improved Leakoff Control for Fracture Acidizing

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract Improvements in leakoff control in deep penetrating fractures have been accomplished penetrating fractures have been accomplished by the use of viscous, nonreactive fluids and viscous, non-reactive fluids containing fine sand when used in alternate stages with acid. Macro examination of hairline fracture vugs and large pores and examination under the scanning electron microscope coupled with laboratory fluid loss data explain how the pad fluid and pad fluid containing fine sand can control fluid leakoff. Another facet of this investigation has been a study and analysis of pressure variations during fracture treatments. This contributes further evidence of the influence of a leakoff control mechanism. These data, although possibly subject to different interpretation, can be shown to confirm the premise of leakoff control by inert pads sandwiched between stages of acid while acid fracturing. Introduction Many improvements have been made in acidizing since the first commercial acid job in 1932. One of the most important advances has been the recognition that fracturing was occurring in the majority of acidizing treatments. Injection rates of most early acidizing treatments were high enough to cause fracturing, but this was called "breaking down" the formation. It was recognized that a "breakdown" had to occur if the job was going to be a success. Since acidizing is now recognized as a fracturing process, the use of fracturing principles are being used to increase live principles are being used to increase live acid penetration into the rock. Although use of these principles has improved treatment design, the actual results obtained by fracture acidizing carbonate formations have not matched the increases predicted by computerized design programs. Much research has been directed programs. Much research has been directed toward reducing the difference between actual and predicted results. Some of the approaches taken have included:Acid retardation.Increased acid concentration.Increased injection rates.Increased fracture width to decrease area-volume ratio.Improved matrix leakoff control.Increased pad volumes.