Fate of Alpha-Amylase Used to Degrade Starch in Water-Based Drilling Fluids

Abstract

The removal of water-based mudcakes (filter cakes) from horizontal sections is a difficult task. The use of the enzyme α-amylase in enzymatic degradation of mudcake has proven conditionally effective in laboratory and in field treatments. Even so, the fate of the enzyme after treatment and the product distribution formed during treatment is unknown. This thesis presents a method of characterizing the mudcake-enzyme (specifically the starch-α-amylase) degradation system using analytical methods adopted from established biochemistry techniques. These methods were used to compare the effectiveness of the enzyme degradation system under various degradation conditions.

The enzyme’s thermal tolerance under High Temperature/High Pressure (HPHT) conditions were determined using mud aging cells. Enzyme baseline activity (defined as rate of starch degradation) was established under well-mixed reaction condition. All enzyme treatment tests were performed in HPHT filter press to simulate downhole conditions. Retained permeability was determined for each test and concentrations of enzyme and unreacted starch was determined using UV-Vis spectroscopy. Starch degradation reaction product distribution was determined using high performance liquid chromatography coupled with refractive index detection (HPLC-RID).

Experimental results show that the specific company provided enzyme is not effective in degrading filter cake at any of the tested temperatures and that the analytical methods developed were effective in characterizing the starch-α-amylase reaction system.