Abstract
The paper highlights the successful application of a new single-phase, polymer-free delayed acid fluid technology for re-stimulation in an offshore well in Brazil's pre-salt field. The study's objective was to evaluate the effectiveness of this new system in bypassing near wellbore formation damage and to compare it with the conventional emulsified acid system.
The new fluid system underwent extensive lab testing in Houston and Macaé with the support of TotalEnergies Reservoir Wellbore Interface (RWI) in Centre Scientifique et Technique Jean Féger (CSTJF) before being utilized for the re-stimulation job. Propriety matrix acidizing software was employed to optimize the job design, volumes, pumping rates, and diversion strategy. The treatment design aimed to ensure acid coverage along the wellbore of a multizone well and radial extension to bypass formation damage. The treatment was verified by pre-treatment and post-treatment production logging tool (PLT) analysis. Prior to the main acid pumping, an acid prewash with coiled tubing equipped with a pulsating pressure waves tool was performed. The acid pumping plant was arranged on a modified platform supply vessel (PSV), which significantly reduced the costs involved with a dedicated Stim Vessel. The treatment was performed successfully utilizing modified PSV) via a drillship to the subsea well. The acid pumping plant arranged on PSV was a unique project, where a full Stimulation Plant was assembled on the main deck of the support vessel, significantly reducing the costs involved with a dedicated Stimulation Vessel.
The new single-phase, polymer-free delayed acid fluid technology resulted in an overall skin reduction from -0.8 to -4.0, despite the variations in permeability observed in different zones. The system was successful in treating all three zones as planned, leading to an incremental production increase of 17% on barrels of oil per day (bopd) after well production stabilization and an increase in production index (PI). The effectiveness of the system was confirmed by Production Logging Tool (PLT) analysis before and after the treatment. Using the new acid fluid simplified operations compared to the emulsified acid system used previously in the initial stimulation, reducing rig time for the job execution. The new single-phase, polymer-free delayed acid fluid technology is considered a suitable candidate for treating multiple zones with permeability variations in Brazil's pre-salt formations.
The new acid fluid technology is an efficient alternative to the conventional emulsified acid system, which is logistically more complex and less environmentally friendly. The results of this study provide practical guidance for practicing engineers working on re-stimulation operations in offshore wells with near wellbore formation damage.
