A.M. Przepasniak, Department of Chemical Engineering, The University of Alabama, and P.E. Clark, Department of Chemical Engineering, The University of Alabama
Formation damage by polymers used in drilling, workover, and completion fluids can be a significant problem. In many of the processes that occur in the oilfield, fluid-loss agents are added to the fluids to minimize the loss of polymer containing fluid to the formation. It is well known that certain polymers will filter out on the formation face while other polymers freely enter the matrix. Some polymers will filter in low permeability rock while flowing freely in high permeability rock. This leads to the question of polymer filtration in fluid-loss agent and drilled solids filter cakes.
Hydroxyethyl cellulose (HEC) and xanthan gum were the two polymers used in this study. Both of these fluids find wide application in drilling, completion, and workover fluids. Initial studies were carried out with polymer concentrations of one and two pound per barrel (0.29 and 0.57% by weight respectively). Bentonite, rev dust, and calcium carbonate were used in the concentration range of one to twenty pounds per barrel (0.29 to 5.8% by weight) for the filter cake material. Two different experimental protocols were used in the study. The first experimental protocol consisted of slurrying the solid material in brine, filtering a known amount of the slurry, flowing a clear brine through to establish the permeability, and then flowing a known amount of polymer solution through. The polymer solution effluent from the cell was collected in three different segments. The rheology of each segment was then compared to the rheology of the initial polymer solution. The second protocol consisted of slurrying the solid material directly into the polymer solution and filtering the slurry in the filter press cell. Again, samples were taken and the rheology compared with the rheology of the initial polymer solution.
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