Development of Hybrid Drilling Fluid and Enzyme-Acid Precursor-Based Clean-Up Fluid for Wells Drilled with Calcium Carbonate-Based Drilling Fluids.

Abstract

Significant formation damage can occur during drilling operations because of the invasion of drilling fluid fines and filtrates that lead to pore blocking and saturation alteration mechanisms. This study demonstrates the ways to minimize drilling fluid-related damage and the removal of the deposited filter cake in the carbonate reservoir through judicious selection of bridging particles using “ideal packing theory” and formulation of an enzyme-based clean-up fluid with an acid precursor. The polymer-based drill-in-fluid with a mixed grade of CaCO3 bridging particles resulted in a compact filter cake with reduced filtration loss preventing internal pore damage significantly. Several ester hydrolysis reaction kinetics were studied, and finally, one combination was chosen as the suitable acid precursor because of its ability to generate a required concentration of acid within the downhole condition. The return permeability of mud-damaged carbonate core plugs was higher than 95% after exposure to the clean-up solution. The corrosion rates were found to be significantly below the industry limits, and the use of acid corrosion inhibitors is eliminated.