Browsing by Subject "filter cake"
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Item Analyzing the Limits and Extent of Alpha-Amylase Catalyzed Removal of Starch-Based Filter Cake(2012-02-14) Dharwadkar, Pavan S.The ability of starch to impart functions including fluid-loss control, cuttings transport, and rheological characteristics to water-based drilling fluids has led to its widespread use in the oil industry. The filter cake deposited by these drilling fluids often employs sized solid particles and starch to inhibit fluid loss into the formation. This inherently causes damage to the formation by impairing the permeability and must be removed before production. An alpha-amylase enzyme treatment was found to provide an effective approach to degrading starch in filter cake. In this work, an alpha-amylase enzyme treatment was analyzed by determining the extent of degradation of starch in filter cake using the iodine test, identifying degradants using high performance liquid chromatography, spectrophotometrically monitoring the concentration of enzyme, and measuring the cleanup efficiency of the enzyme treatment using a static filter press apparatus. The alpha-amylase enzyme used in this study was found to have a molecular weight under 30,000. The activity of the alpha-amylase enzyme was found to be sensitive to pH and temperature. The alpha-amylase enzyme was found to denature at temperatures above 165 degrees F and reversibly deactivate at pH below 4. Optimal conditions for alpha-amylase activity were found to be 150 degrees F and pH 6.5. The enzyme treatment works by hydrolyzing the interior glycosidic bonds of amylose and amylopectin residues of starch, creating soluble poly- and oligosaccharides and glucose. The enzyme treatment did not dissolve the calcium carbonate sized solids and a 5 wt. % hydrochloric acid postflush was necessary. The cleanup efficiency of the enzyme at pH 6.5 and room temperature treatment in conjunction with the postflush in a static test was 73% at 10% v/v concentration. Degradants resulting from alpha-amylase were identified chromatographically. Enzyme concentration remained steady prior to and after treatment.Item Characterization of Filter Cake Buildup and Cleanup under Dynamic Fluid Loss Conditions(2011-10-21) Yango, TakweHydraulic fracturing is a popular stimulation method in tight gas and shale gas reservoirs that uses a viscous fluid to fracture the reservoir rock and uniformly transport proppant to create a highly conductive path that is kept open by the proppant after fracturing. This method is used to improve the productivity of the otherwise low permeability reservoirs. Hydraulic fracturing, though in general beneficial, is a complex process that has a number of challenges in fracturing design and execution. This research focuses on studying the damage caused by the fracturing fluid (gel) to the fracture and the conditions to remove the damage. Guar gum and its derivatives have been the most commonly used polymers to increase the viscosity of fracturing fluids. The fracturing fluid gets dehydrated under pressure leaving behind a highly concentrated unbroken residue called filter cake which causes permeability impairment in the proppant pack, resulting in low fracture conductivity and decreased effective fracture length. This study seeks to characterize filter cakes. By measuring its thickness and with the leak off volume, the concentration and yield stress of the filter cake can be estimated. The thickness of the filter cake was measured with a precise laser profilometer. Correlations are proposed to estimate filter cake properties (thickness, concentration and yield stress) based on pumping conditions (pump rate, time and net pressure) and rock properties. With these properties known, a required flow back rate of the reservoir fluid can be estimated to clean up the filter cake modeled as a non-newtonian fluid exhibiting a yield stress. Typical field conditions were referenced and scaled down in the lab to closely represent the field conditions. Recommendations are provided on gel damage based on the observation of the study.