Perforation breakdown

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. 

B-1. Perforation breakdown treatment (used in the United States,... 

Short-time tests also can give misleading results on alloys that form passive films, such as stainless steels. With Borderline conditions, a prolonged test may be needed to permit breakdown of the passive film and subsequently more rapid attack. Consequently, tests run for long periods are considerably more reahstic than those conducted for short durations. This statement must be quahfied by stating that corrosion should not proceed to the point at which the original specimen size or the exposed area is drastic y reduced or the metal is perforated. 

A spearhead or breakdown fluid followed by the cement slurry is circulated downhole with the packer by-pass open. This is done to avoid the squeezing of damaging fluids ahead of the slurry. A small amount of back pressure must be applied on the annulus to prevent the slurry fall caused by U tubing. If no tail pipe has been run, the packer by-pass must be closed 2 or 3 bbl before the slurry reaches the packer. If the cement is to be spotted in front of the perforations, with the packer unset, circulation is stopped as soon as the cement covers the desired zone, the tail pipe pulled out of the cement slurry and the packer set at the desired depth. The depth at which the packer is set must be carefully decided. 

Localized corrosion is the direct result of the breakdown of passivity at discrete sites on the material surface. As was stated above, once passivity is established on a surface, one might expect either that it would remain passive or that a complete activation of the surface would occur. However, what is often observed in practice is the appearance of discrete areas of attack that begin to corrode actively while the vast majority of the surface remains passive. These isolated regions of attack are more than mere annoyances the local penetration rates can be on the order of 10 mpy or higher, leading to rapid perforation of any reasonably sized container. Since the original intent in using passive materials (e.g., CRAs) in any application is to exploit their low dissolution rates, localized corrosion can be a major operational problem. 

Localized corrosion of metals and alloys occurs in aggressive media (e.g., containing chloride) as a consequence of the passivity breakdown, with major impact in practical applications and on the economy. This form of corrosion is particularly insidious since a component, otherwise well protected by a well-adherent, ultrathin oxide or oxyhydroxide barrier layer (i.e., the passive film), can be perforated locally in a short time with no appreciable forewarning. Extensive studies have been conducted over the last five decades to understand localized corrosion by pitting [1-10], but the detailed mechanisms accounting for the local occurrence of passivity breakdown remain to be elucidated and combined with kinetics laws to allow reliable prediction. 

Bell (1975) used the C02-diethanolamine system to evaluate area-averaged mass fransfer performance of a range of smooth, mesh and perforated discs. Once again the smooth disc gave the lowest mass transfer coefficient, while the perforated and mesh discs were broadly similar. For all the discs a pronounced maximum coefficient was noted at a critical rotational speed. This phenomenon was asalbed to film breakdown in the peripheral regions of the discs as the rotational speed increased. The existence of peripheral dry areas was confirmed photographically. 

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. 

Never exceed the breakdown pressure of the formation in a sandstone acidizing treatment, unless absolutely necessary initially to break down the perforations (with a perforation wash tool) or to bypass severe damage to initiate injectivity. 

---