Perforating fluid, perforation cleanup, and breakdown

In carbonate formations, acetic add (usually 9% or 10%) is an effective perforating fluid. It may also be weighted up by inclusion of salt, if required. Acetic is a mild add but strong enough to dissolve perforation debris, resulting in clean perforations. If necessary following well completion, perforations may be cleaned or stimulated further with a small acid treatment, typically acetic acid (10%-15%) or HCl (7.5%-15%). 

Perforation breakdown, conducted to initiate production, may also be performed. Acid is injected above fracturing pressure to break down the perforations and create communication between the formation and the wellbore. 

If a well is to be completed with a hydraulic fracturing treatment, perforation or formation breakdown prior to injection of fracturing fluids is a common need. Injection can be initiated by pumping thin acid (usually HCl) or a slick HCl solution (slightly gelled) to break down perforations and initiate fluid entry into the formation. In practice, this enables easier placement of fracturing fluids and proppant in a hydraulic fracturing treatment. 

Strong acid, such as HCl, will typically form longer, single wormholes extending from the perforations. If add is not effectively diverted, a matrix treatment with conventional HCl may create only one wormhole. This wormhole will then accept all add injected, as it will be the increasingly conductive path of least resistance for add as it continues to be injected. 

Fracture acidizing can be used to bjqjass formation damage in a carbonate formation. For damage b)qjass, a long fracture may not be needed. The purpose would be similar to that of a frac-and-pack procedure in a sandstone formation. In that case, a propped fracture with length and conductivity suffident to effectively extend the wellbore radius beyond a damage zone is all that is needed— not an extensive, propped fracture. 

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