Drill-in fluids contains biopolymers such as xanthan gums,cellulose and/or starch along with bridging agents like sizedcalcium carbonate particles. These polymers are used toenhance the carrying capacity of the mud and to form a filtercake on the formation to minimize leak-off of the drillingfluids into the formation.Proper removal of drilling mud filter cake is essential tominimize formation damage. The damage becomes moreintense in tight formations, especially in horizontal gas wellswhere the draw down is not high enough to dislodge the filtercake. Another source of damage is the mud filtrate wherewater blockage can occur in tight formations, especiallysandstone reservoirs.Thorough lab and field investigations of formation damageinduced by drill-in fluids (water based mud) were conducted.A mini-flow loop was used to assess formation damagedinduced by various polymers present in the drill fluid. Variouscleaning fluids were examined and their effectiveness inremoving the filter cake was determined. The cleaning fluidsincluded: specific enzymes, mild acids, surfactants and mutualsolvents, and combinations of these fluids. The retainedpermeability of reservoir cores was determined for eachcleaning fluid. This paper presents results obtained from thelab and recommendation made for field application. Fieldtreatment was conducted in a horizontal gas well whichresulted in significant increases in gas production.
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