Enhanced Drill-In Fluids to Preserve Reservoir Permeability – From Development to Field Application

Abstract In the current drilling and completions market, operators are requiring fluids that minimize reservoir damage, stimulate while drilling, completing, and cementing wells, and drive reduction in carbon footprints. Reservoir impediment due to incompatibility between the native reservoir fluids and the drill-in, completion, and cementing fluids is a common cause of damage in depleted formations. High fluid invasion during the various phases of the well construction can further exacerbate these incompatibilities. Compatibility studies between reservoir and wellbore construction fluids built from industrial waters should be analyzed in detail and tested extensively before starting operations. A detailed compositional analysis (including cation, anions, and functional groups) of the water used to prepare the fluids is required to prevent scale deposition and emulsion formation. To maintain reservoir permeability and minimize damage from fluid incompatibilities, emulsion formation should also be minimized by using fluids with the ability to maintain the water-wet condition of the reservoir and reduce interfacial tension (IFT) between the crude oil and water-based fluids thus reducing capillary pressures. Additionally, the bridging and weighting solids should be properly sized to prevent plugging of the rock pore throat, as well as minimizing solids accumulated while drilling. This paper discusses the efficacy of formation damage prevention by combining and adding an IFT reducer, a scale inhibitor, and a fines migration preventer into the drill-in and completion fluids. Several tests were performed to prove the concept, including return permeability using a sequence of fluids (reservoir, drill-in, and completion fluids), interfacial tension measurements, and compatibility analysis. Laboratory data have shown that pH changes generated by some filtrates invading the near-wellbore area, such as cement filtrate, drastically increase chemical reactions and promote scale formation. It was possible to see the nucleation and salt precipitation processes by extending the evaluation time from 8h to 24h. In consequence, the effective flow area in the near-wellbore is reduced by scale formation, impeding the production. Studies were focused on the compatibility between reservoir fluids and drill-in and completion fluids. The combination of the IFT reducer, scale inhibitor, and fines stabilizer in the water-based fluids resulted in minimization of formation damage by preventing scale formation and fines mobilization and by minimizing the potential for emulsion formation by reducing interfacial tension and controlling high capillary forces present in very low permeable formations. A baseline return permeability test (without enhancer package) showed around 25% reduction in permeability after exposure to the drill-in fluid and/or completion fluid, but when the IFT reducer and scale inhibitor are added, the return permeability is only reduced <10%. The combination of products helps to reduce formation damage and promote good permeability in the near wellbore area.