Experimental Study of a One-Step Multifunctional Treatment Fluid for Water-Based Mud Filter-Cake Cleanup

Abstract

Summary Filter-cake cleanup following the drilling and completion operation is important for reestablishing communication between the formation and wellbore. A dual-action cleanup system for water-based mud (WBM) was developed to dissolve the calcium carbonate (CaCO3) bridging agent and polymeric materials present in the filter cake. The novel treatment fluid contains a high concentration of nonencapsulated oxidizing salts and delayed acid generating materials and is gelled with a viscoelastic surfactant (VES)-based surfactant. The fluid provides many advantages over traditional fluids as it does not generate any residue on breaking, unlike the traditional polymeric gelling agent. The breakage or reduction in viscosity of this fluid can be accomplished by contact with the produced oil thereby disrupting the micelles. Traditional polymers on the other hand are broken by oxidizers, and if delayed breakage is desired, the breaker needs to be encapsulated. Another benefit of this system is that the VES gelation may enhance uniform filter-cake cleanup in extended reach horizontal sections of the wellbore. The novel fluid system contains a strong oxidizer, namely, sodium bromate (NaBrO3), that activates at temperatures above 160oF causing the breakdown of the polymer contained within the filter cake without affecting the VES surfactant or gelation which helps in mixing the fluid at the surface. Finally, the fluid contains an acid-generating precursor that is neutral at ambient temperature conditions. Once the fluid is heated up in the formation, acid is generated via ammonium oxidation, thereby lowering the viscosity of the gel and dissolving the CaCO3 bridging material. In summary, the fluid that can be prepared on the fly accomplishes multiple functions ranging from controlled gelation to clean break without residue or outside intervention to dissolution and degradation of inorganic and polymeric components.