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AbstractThis paper presents field data from the acidizing of several horizontal, gravel-packed, water injection wells in the deepwater field of Marlim Sul, Campos Basin, Brazil. We describe the keys to the strategy that led us to achieve highly successful results, which involved changes in the composition of the drill-in fluids (DIF), the use controlled acidizing parameters and special acidizing tools that provide mechanical diversion, and modifications in the conventional acidizing program, that made fluids compatible with the acidizing tools. Since the main type of damage present in the wells is the mudcake from the DIF, small acid volumes are able to remove all damage. The small damage penetration also recommends low injection rates, instead of the traditional high rates that would not provide enough contact time to dissolve the damage and would create preferential paths for the acid.Before the use of the new strategy, the injections wells in Marlim Sul were treated with regular wash pipes, with no guarantee of mechanical diversion, and poor results. After starting to use specially designed acidizing tools (one-trip or straddle packer), and to minimize solids and filtrate in the DIF, the average completion efficiency (CE) after the treatments became 77%, what delivered injectivity indexes far above the injection quotas defined by reservoir engineering. A subsequent improvement was to start acidizing the whole horizontal section, instead of only the points of higher damage, as shown by the flowmeter logs. This has made the final completion efficiencies come very close to 100% for all treatments. As a consequence of that, and of the good results also obtained in the producer wells, the production platform P-40 became overloaded with oil and a new production facility, FPSO-Marlim Sul, had to be added to the project to accommodate the extra oil. Due to the good results obtained, all the other deepwater fields at the Campos basin adopted the same strategy for acidizing their horizontal injectors.The outline of the strategy presented in this paper may be helpful for improving the results of acidizing jobs of horizontal water injectors in similar offshore fields around the world. The pioneer application of special acidizing tools, the modifications in the DIF composition, and the use of controlled acidizing parameters constitute very important advances for the complex task of acidizing horizontal wells.
