Overcoming Conventional Limitations: An Advanced Emulsified Filtercake Removal Fluid for Extended Reaction Time

Abstract Water-based reservoir drill-in fluids (RDFs) often deposit a filtercake composed of polymers (such as starch or biopolymers) and acid-soluble bridging agents (e.g., calcium carbonate) on the wellbore. Effective removal of this filtercake prior to production is critical to avoid formation damage and impaired well performance. Conventional filtercake cleanup methods have significant limitations under high-temperature conditions. Strong acids (e.g., HCl or organic acids) react too rapidly and non-uniformly, creating localized breakthroughs and leaving portions of the cake intact. Enzyme-based breakers offer gentler, more uniform polymer degradation but historically lack thermal stability at high temperatures. Chelating agents can slowly dissolve CaCO3 with less corrosion but their efficiency drops and reaction rate accelerates undesirably at elevated temperatures. Acid precursors that hydrolyze to release acid over time have shown promise for delayed reaction, yet conventional designs fail to maintain sufficient delay beyond ~24 hours at temperatures above 200 °F (93 °C). In practice, many high-temperature wells have struggled to achieve uniform filtercake removal because available breaker fluids either react too quickly or degrade under prolonged heat exposure. This paper presents a novel emulsified fluid system for filtercake removal designed specifically to overcome high-temperature limitations. The innovation lies in extending the application of emulsified acids from matrix acidizing to wellbore cleanup and filtercake dissolution. By incorporating enzyme into the emulsified organic acid formulation, the system targets both major filtercake components: the enzyme slowly degrades polymeric binders, while the emulsified organic acid provides controlled, delayed dissolution of the CaCO3 bridging solids. Laboratory filtercakes were generated using lab-prepared water-based mud (WBM), comprising a low-solids, non-dispersed, water-soluble polymer-based drilling mud with acid-soluble bridging and weighting agents. Thermal stability tests were conducted on the new emulsified filtercake removal fluid at 200 °F for various periods of time by aging the fluid in sealed high-pressure/high-temperature (HP/HT) cells at 200 °F and examining any phase separation. Dissolution efficiency tests were then performed by exposing the lab-prepared filtercake samples to the emulsified filtercake removal fluid at 200 °F for 1, 3, and 5days at a ratio of 1:10 filtercake solids to solution and aperiodic solubility measurementwere taken to quantify the extent of filtercake dissolution at each interval. Corrosion testing was conducted by immersing C95 steel coupons in the fluid at 200 °F to measure coupon weight loss and corrosion rate. Results demonstrate that the emulsified filtercake removal system achieved satisfactory dissolution efficiency and improved reaction longevity. The reaction was effectively delayed and controlled which can prevent premature breakthrough and fluid loss. The dissolution increased gradually over days and by the 5-days mark, the emulsified filtercake removal fluid achieved around 50% dissolution of the filtercake, in stark contrast to conventional filtercake removal treatments that would have either reacted instantaneously or ceased functioning by this time. The enzyme was able to operate at 200 °F, breaking down starch in the filtercake as evidenced by an iodine indicator test (no purple staining after treatment, indicating starch elimination). The emulsified acid remained stable throughout the soaking period, releasing acid gradually for sustained dissolution. Thermal stability tests showed that the fluid was stable with no significant phase separation or degradation after 5 days at 200 °F. Corrosion impact on C95 steel was minimal and the fluid exhibited a low corrosion rate, attributed to the acid beingsequestered in the oil phase. In summary, the developed emulsified filtercake removal system provides a single-step, high-temperature filtercake breaker that offers extended reaction time and uniform cleanup, overcoming the 24-hour limit of conventional systems.