Terry D. Monroe

Factors affecting the performance of enzyme breakers for removal of xanthan-based filter cakes

The use of enzymes as an external breaker for removal of xanthan based filter cakes has exhibited cost savings and effective clean up in several open-hole horizontal Gulf Coast wells. Enzymes are specialized proteins produced by cells of living organisms. They act as catalysts to promote specific reactions. Polymer-specific enzymes hydrolyze xanthan resulting in non-damaging fragments. As a catalyst, the structure of an enzyme is unchanged by the reaction it promotes; therefore, the enzyme has the ability to initiate another reaction. The reactivity of the enzyme is essentially infinite with the exception of damage to the enzyme by chemical, thermal, or mechanical means, i.e. denatured. Xanthan-specific enzymes degrade or cleave either the α - 1,2 or β - 1,4 glycosidic linkages of the substituent and the β - 1,4 linkages of the backbone. Recent laboratory investigations revealed several factors, which can control the effectiveness of an enzyme. These factors include xanthan quality, iron, base brine and hydrocarbons. These factors can function as barriers and prevent the enzyme from cleaving specific linkages of the xanthan structure. This study presents guidelines for formulating an enzyme compatible xanthan based drill-in fluid for open-hole horizontal completions. These gvidelines were recently applied to two recent open-hole horizontal completions in the Gulf of Mexico that yielded optimum results.