Horizontal carbonate reservoir stimulation has attracted considerable attention in the past decade as one of the major areas for development in matrix stimulation engineering. Modern technologies have enabled technically suitable interventions in extended and even mega-reach wells. In the Middle East especially, carbonate field development strategies have used mega-reach wells as the main technique in achieving the highest possible reservoir contact. In such a case, coiled tubing (CT) intervention becomes a necessity.
With carbonate acidizing, since more than 50% of the matrix is soluble in acid, the objective is to bypass the damage and increase the productivity by creating new highly conductive channels called wormholes. The success of a treatment is a function of fluid penetration, acid reactivity, injection rate and diversion. To increase the success of the treatments, improvements have been made recently in injection rate and diversion using the latest technologies in CT intervention. The introduction of CT provides significant advantages in stimulation execution, yet imposes some challenges. Real-time downhole measurements using fiber optic telemetry have been used frequently to improve chemical diversion and fluid placement. However, pumping rates have been significantly limited to a maximum of 2.0 bbl/min when this technology is deployed.
Extensive engineering work was invested in solving this challenge. The main objective was to obtain the optimum diversion using downhole “point” and distributed measurements without sacrificing the high injection rates. In response to this need, modifications to the existing downhole measurement system were introduced enabling pumping of rates beyond 5.0 bbl/min. The key focus of the redesign was the repackaging of the downhole tools as well as the telemetry link to surface, resulting in expansion of the operating envelope of the technology.
Yard testing has been completed, and results have been encouraging. The solution has been piloted in the field, and a field case study showed remarkable injectivity improvement.