Investigating the compatibility of enzyme with chelating agents for calcium carbonate-filter cake removal

Removal of water-based filter cake that formed either during drilling or hydraulic fracture operations is a difficult task. Chelating agents were introduced in the oil industry to solve the common problems associated with the conventional acids (hydrochloric acid, an organic acid, or a mixture of these acids), such as rapid and uncontrolled reaction rate and corrosion to well tubulars, especially in horizontal and deep wells. The objectives of this study are to (1) assess the reaction of starch with different chelating agents (GLDA, EDTA, DTPA) at different conditions of pH and temperature, (2) evaluate the compatibility of chelating agents with HTA enzyme (a-amylase enzymes), (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 period (12 hrs) at 200°F. These chelating agents were incompatible with a-amylase enzyme (HTA enzyme), which was able to completely break the starch in 6 hrs at 200ºF. The best scenario to remove the calcium carbonate filter cake is to soak the filter cake with use a-amylase enzyme for 6 hrs and after that soak the filter cake with GLDA (20 Wt%, pH 4) for 16 hrs.