Abstract

In the Gulf of Mexico the wells are usually completed as cased and perforated or frac packed. These wells can be damaged during the drilling phase, completion phase and/or when they are on production. This paper presents the unique combined use of chelant and mud acid treatments to remediate a deepwater Gulf of Mexico well with severe formation damage. Fluid qualification work optimized the treatment, which was deployed using both coiled tubing and bullheading methods. Surveillance, surface read out and memory, were utilized throughout the intervention to understand the effectiveness of each treatment, along with final fluid analysis.

Both coiled tubing and bullheading were used for specific purposes. Given the completion design configuration, a mud acid screen wash was deployed using coiled tubing to clean the screens and improve near-wellbore access. Care was taken to avoid reacting low pH mud acid with high pH chelant. This reaction would reduce the benefits of each treatment, in addition to risking precipitation of by-products in the reservoir. Therefore, the operation was sequenced such that additional flowbacks allowed for reservoir clean-up prior to the next fluid deployment. Lab testing showed multiple soaking and refreshes of the slow-reacting chelant was optimal. A final mud acid bullhead treatment was deployed to matrix stimulate and treat the reservoir 3 - 5 feet into the near-wellbore region. During the operation, several forms of surveillance were planned to understand the effectiveness of each chemical treatment. This included temperature surveys, surface flowback samples analysis to understand the effectiveness of the treatments, and spinner information to quantify zonal contribution.

Post-production results showed an improvement in overall well productivity due to a reduction in formation damage. These results are supported by in-well surveillance and post-intervention fluid analysis. The most basic of all measurements, temperature, proved to be the most effective in understanding damage removal evolution and reservoir contribution throughout the intervention.

This paper will present the novel combined application of mud acid and chelant stimulation treatments to remediate a frac packed well with combined severe initial well construction damage and post-production formation damage.

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