Protecting the Reservoir With Surfactant Micellar Drill-In Fluids in Carbonate-Containing Formations

Summary Conventional water-based drill-in fluids (DIFs) contain high-molecular-weight polymers and different-size-distribution solid particles to reduce fluid loss and carry drilling debris back to surface during the drilling process. The polymers and solid particles in the drill-in fluids usually generate near-wellbore formation damage. This paper introduces a new polymer-free and solids-free surfactant micellar-based drill-in-fluid system to drill a carbonate-containing reservoir. This new fluid system contains relatively low-reactivity acids mixed with surfactants and internal breakers. The drill-in fluid is designed to have low viscosities in the drillpipe. After the fluid flows out of the drill bit, the acids will react with carbonates in the formation and thereby increase the pH of the drill-in fluid. The higher fluid pH combined with the presence of dissolved divalent ions will cause the surfactants to form elongated micelle structures that will significantly increase fluid viscosity at the bottom of the hole and in the downhole annulus between the drillpipe and the formation rock. The viscosified drill-in fluid will reduce fluid loss and will carry nondissolved drilling debris to the surface. After drilling through the targeted formation, the internal breakers in the viscosified drill-in fluid will break down the fluid viscosity to improve ease of removal, and the drill-in fluid should leave very little or no near-wellbore damage.