The Feasibility of Autonomous Flow Control Devices for Matrix Acid Stimulation Operations in Carbonate Reservoirs

Abstract The matrix acidization operation has been extensively associated with unconformity. The challenge remains to distribute the acid treatment fairly along the wellbore. It has been observed that acid prefers the less resistance spots along the wellbore which are characterized by high permeability streaks / fractures. During the operation, the injection to these areas is highest which further increases its permeability whereas low permeability zones never receive the similar treatment and are left out with lower permeability. To counter this challenge, an approach of utilizing an advance completion consisting of Autonomous Outflow Control Device's (AOCD) was implemented. Although there are multiple case histories of successful installation of AOCD in water injection wells for conformance, the high rate of stimulation operation poses a major challenge. This study involves developing a methodology to ascertain that a similar performance of acid stimulation can be achieved with much lower rates through optimization. This will be possible by conforming stimulation fluids through the wellbore, allowing operation to be executed at lower rates than Open hole or standard completion. The solution will also provide cost effectiveness as a much less volume of fluids will be required to produce better performance as compared to non-optimized completion. The study also involved upgrading a stimulation software to convert it into a fit for purpose platform which will incorporate the operational envelope of AOCD. The AOCD is a rate-controlled device. At the heart of the device is a spring-based mechanism that reacts to the pressure drop/flow rate across the nozzle. Once a predefined upper flow-rate limit is reached at a zone, the valve autonomously closes. This eliminates the impact of the thief zone on acid injection conformance and maintains a prescribed acid distribution. The technology is proven in water or polymer injection wells; this study highlights the value addition that AOCD can bring to matrix stimulation operations; further presenting AOCD as a fit for purpose solution for injection wells irrespective of the injection type or application. A novel approach is developed through modelling to display that Autonomous Flow Control Devices can provide substantial value in stimulation operations. This will enable the operators to minimize the impacts of heterogeneity on the acid conformance and the completion system will autonomously respond to a dynamic change in reservoir properties, specifically the growth of wormholes.