A Novel

Cleanup of drilling-fluid filter cake in long horizontal and multilateral wells is a difficult task. Both mechanical and chemical means (acids, oxidizers, chelating agents, and enzymes) have been used in the field. However, these methods have serious limitations and can affect well performance adversely. Acids and oxidizers are very reactive, but are nonspecific. Enzymes can be used to degrade starch and xanthan polymers. The major limitation of enzymes is their inability to stay active at temperatures greater than 200 degrees F. The activity of enzymes at 207 degrees F was less than 10% of their activity at 200 degrees F. Previous studies to increase the stability enzymes were aimed at: (1) changing salinity, (2) changing the source of the enzymes, (3) using additives that alter the conformation of enzymes, or (4) modifying the enzymes chemically. These techniques did not maintain the activity of the enzymes at 200 degrees F. For filter-cake removal, enzymes have been used globally at higher temperatures, though their activity is known to be much less than 2%. This paper examines the use of chemicals that function as a stabilizer for enzymes up to 250 degrees F. Optimized concentrations of this stabilizer not only inhibit the coagulation of enzymes at these high temperatures but also maintain the activity of enzymes at the high temperatures that are encountered in the oil field. Laboratory studies on the stability, compatibility, and filter-cake-damage reversal were conducted with stabilized-enzyme formulation. Experimental results indicated that the new proprietary enzyme stabilizer was very effective in eliminating the deactivation tendency of enzymes at high temperatures. Conventionally, enzymes coagulated at temperatures greater than 140 degrees F and charred when exposed to temperatures greater than 200 degrees F, but in the presence of the stabilizer, precipitation and burning were not observed. When using an enzyme at high temperatures without the stabilizer, the burned residue accumulated on the surface, resulting in a thin film that reduced the permeability of the cake even further. High-pressure/high temperature (HP/HT) filtration studies using the enzyme stabilizer showed that this film was not formed, which resulted in a cake with much higher retained permeability.