Single-Stage Chemical Treatment for Oil-Based Mudcake Cleanup: Field Case and Laboratory Studies

Abstract

Abstract Formation damage minimization and removal are important factors in enhancing field productivity and achieving targeted production rate. While formation damage is anticipated during drilling, an effective wellbore cleanup fluid becomes essential to remove mud damage and enhance well productivity. Filter cake layer created by drilling fluid can impair production considerably and should be removed prior to production using an effective treatment. Filter cake can be removed using a chemically designed filter cake removal treatment. The design of the treatment requires considerations of mud type and reservoir conditions. Also, it is important to consider the compatibility aspect of the treatment fluid with formation fluids and drill-in fluid base oil. Incompatible fluids result in precipitation which leads to further formation damage. In Saudi Arabia, many sandstone reservoirs are drilled with invert emulsion drill-in fluid to avoid the risk of clays swelling, which can lead to hole sloughing and formation damage. However, production impairment due to mud damage effect was observed in some horizontal wells drilled with invert emulsion drill-in fluid and completed with stand-alone screens as a result of improper mud managemet. After being put on production, their production rates have been reduced significantly with time. The decrease in production was related to screen blockage and mud cake impairment. A newly developed single-stage treatment was spotted and soaked to remove oil based mud cake and screen blockage. A significant sustained improvement in production was noticed and flowback solids indicated removal of screen blockage and mud cake. Lab studies were conducted at reservoir simulated conditions to evaluate the effectiveness of the treatment. The study covered testing the treatment filter cake removal efficiency, return permeability tests with reservoir core samples, and compatibility tests with formation fluids and drill-in fluid base oil. This paper will discuss in detail the laboratory work conducted and the successful field treatment performed.