Proposal
As part of a comprehensive program to develop delayed filter cake breakers, a drill-in fluid with magnesium oxide (mag-ox) bridging particles and an ammonium chloride-based cleanup solution was developed. The mag-ox particles are insoluble in water and standard drill-in fluid-based brine such as sodium chloride, but these particles are readily soluble in ammonium chloride or ammonium citrate. Thus, an ammonium chloride-based cleanup can be formulated that will dissolve the bridging particles and other drill-in fluid components without using acid-based systems. Because this technology was of specific interest for injector well applications, a laboratory study was undertaken to evaluate this novel system. This paper summarizes laboratory work and radial flow loop test results, and discusses possible field applications.
Filter-cake cleanup of injection wells can be especially problematic because operational constraints often preclude backflowing the well to remove the residual filter cake. Consequently, injection remains impaired if the residual filter cake is not removed by other means. The highly reactive nature of standard treatments may remove the filter cake at the point of circulation before the treatment can be placed over the entire openhole interval. A need exists for cleanup solutions that have a delayed effect on filter-cake integrity, allowing the cleanup solution to be circulated across the entire interval. Preferably, the treatment's reaction with the filter cake would commence when the entire solution is in place and continue until the filter cake is uniformly removed. The ideal placement of a treatment would be in the gravel-pack carrier fluid, where it would provide enough of a delayed reaction to allow the gravel pack to be placed with an alpha/beta wave technique before fluid-loss control is lost.
