Alternative Approach to Acid Stimulation in Extended Reach Multilateral Water Injector Well

Abstract A dual-lateral water injector well was drilled in December 2022 to sustain reservoir pressure and support nearby wells production. A low injectivity of 1,500 bpd was observed from the start of the injection, which was analyzed to be due to tight dolomite formation whereas nearby wells production did not achieve the desired production rates. The objective of the paper is to describe the process of enhancing the injectivity in this extended reach dual-lateral water injector by combining several techniques. Due to the low permeability of the well formation, a work cycle was developed to ensure the successful intervention is executed in a controlled manner. Therefore, acid stimulation treatment was conducted in two runs. Firstly, the long open hole horizontal mother-bore was accessed by means of coil tubing supported with an extend reach vibration tool and a friction reducer, where 185 stages were pumped utilizing special jetting tool. Secondly, an open-hole inflatable packer was run to isolate the stimulated mother-bore. Thirdly, the lateral was treated from the window depth via the coiled tubing/tubing annulus. Finally, inflatable packer was retrieved providing access to both laterals. The main stimulation fluid was chosen to be emulsified acid which provides retardation effect and deeper wormhole penetration. Acid stimulation of the dual-lateral well was a complex intervention using extended reach tool along with friction reducer while selectively stimulating the second lateral using open hole inflatable packer. In the first run, CT reached 15,070 ft till lockup, while original lock-up depth without extended reach methods was expected at 13,691 ft. Total injectivity was improved in both holes whereas post-treatment pressure reduced to 2,100 psi compared to the initial injectivity test of 3,500 psi at 5 bpm. The operator concluded that the anticipated objective was exceeded by increasing the injection rate from 1,500 bpm to 2,500 bpm after bringing the well back on injection. The paper highlights the successful acid stimulation associated with complex intervention executed through coiled tubing and proves the concept of stimulation dual-lateral well without using re-entry downhole tools to access a lateral. This case helps to present the value, challenges, lessons learned and opportunities existing in well stimulation for multilateral that would have previously been deployed through a costlier means of workover operation.