Case Study Analysis of Formation Damage Induced by Brine Workover Fluid on Burcioaia Reservoir (Romania) and Research on Damage Removal Methods

Abstract

Brine workover fluid has a confirmed damage for gas condensate wells generated by both water blockage and fines presented in it. Studied reservoir is a gas condensate field where workover operations performed for replacing downhole equipment have induced severe damage. Formation damage for brine workover fluid was tested on core for both hydrocarbon flowing phases (condensate and gas) and revealed up to four times decreasing in permeability. Laboratory research was then oriented to identify the best solution to remove induced damage. It was tried to identify how much of damage was induced by water blockage and how much by fines present in workover fluid. Tests revealed a good recovery of permeability for gas by using alcohol/surfactant fluids but not close to original permeability. On the other hand correctly formulated mud acid solution have removed induced damage and increased the permeability up to three times more than original permeability. Results have been implemented on field Burcioaia and foam acidizing was used successfully in field tests. For very long perforated intervals foam was used as diverter. In some cases only acid solution was foamed and in other cases also neutral foam was pumped in slugs in between acid stages. Case histories for performed removing damage jobs are also presented.