Investigating the Compatibility of Enzyme with Chelating Agents for Calcium Carbonate Filter Cake Removal

Removal of water-based filter cake formed during drilling and hydraulic fracturing operations is a difficult task. Conventional acids, such as hydrochloric acid, organic acid, or a mixture of these acids, can be used to remove the filter cake. The common issues of these acids are rapid and uncontrolled reaction rate and corrosion to well tubulars, especially in horizontal and deep wells. Chelating agents were introduced in the oil industry to solve the problems associated with the conventional acids. Up to the authors’ knowledge, the reaction of chelating agents with starch, which is a major component of the filter cake, was not investigated in the literature. The objectives of this study are to (1) assess the reaction of starch with different chelating agents, namely ethylenediaminetetraacetic acid (EDTA), glutamic acid diacetic acid (GLDA), and diethylene triamine penta-acetic acid (DTPA), at different conditions of pH and temperature, (2) evaluate the compatibility of chelating agents with enzyme [high thermally stable α -amylase enzymes (HTA)], (3) assess the reaction of enzyme with starch and xanthan gum, and (4) design the best scenario for calcium carbonate filter cake removal. The obtained results showed that EDTA (20 wt%, pH 7, and 12), DTPA (20 wt%, pH 7, and 12), and GLDA (20 wt%, pH 4, 7, and 12) were not able to break the starch after hot rolling for different time periods at 200∘F. Different chelating agents were found to be incompatible with α -amylase enzyme (HTA enzyme that should be used to remove the starch). The two-stage scenario was found to be the best practice to remove the calcium carbonate filter cake in 22 h with 100% removal efficiency and 100% retained permeability. Computer tomography confirmed that external and internal filter cake was completely removed, and no formation damage was existing.