Technical Paper: Effective Matrix Acidizing in Carbonate Reservoir—Does Perforating Matter?

Society: SPE
Paper Number: 105022
Presentation Date: 2007
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It is well known that in cased-hole completions productivity is enhanced by maximizing shaped charge penetration and shot density while minimizing perforation damage. However, in tight carbonate reservoirs, creating deep and clean perforations may still not be enough to generate the desired productivity. Therefore the wells are often stimulated by a matrix acidizing treatment after the perforating. A prevalent mind set in the industry is that acid dissolves the perforation debris and creates wormholes that bypass the perforating and other near wellbore damage, therefore perforating design is not important as long as it serves the purpose of puncturing through the casing.

This paper presents recent research that looks into the impact of perforating on matrix acid stimulation. Large scaled single-shot perforating tests were conducted using real shaped charges to perforate carbonate core samples under downhole conditions. Acid was then injected into the perforations to create wormholes. The acid injectivity was measured, and the wormhole patterns through perforations generated by different perforating designs were compared using CT scans. It was found that clean perforations promote not only higher acid injectivity, but also initiate straighter and more dominant wormholes, while the un-removed perforation debris causes the wormhole to start with a more deviated pattern.

In the paper the required perforating design to create clean perforations is discussed for low permeability gas reservoirs. The effect of perforating with acid in the wellbore as the completion fluid is also examined. The implications and suggestions to safely apply the technique of perforating with acid are discussed.