Evaluation of a New Technique For Removing Horizontal Wellbore Damage Attributable to Drill-In Filter Cake

Many horizontal and highly deviated wells are drilled using the {open_quote}drill-in fluids{close_quote} introduced in recent years. The drill-in fluids are typically comprised of either starch or cellulose polymers, xanthan polymer, and sized calcium carbonate or salt particulates. They were introduced to minimize the mud damage to the wellbore relative to that typically observed with conventional drilling muds. However, testing and experience have shown that insufficient degradation of the filter cakes resulting from even these {open_quote}clean{close_quote} drill-in fluids can significantly impede flow capacity at the wellbore wall. This reduced flow capacity can result in reduced well productivity or infectivity. Consequently, wellbore acid treatments are typically applied in attempts to remove or {open_quote}bypass{close_quote} the filter cake. The acid treatments are often only marginally successful, particularly when applied in extended length intervals. Extensive studies were conducted to develop laboratory procedures to better simulate and characterize the damage attributable to drill-in fluids. Various chemical systems were subsequently applied to evaluate the effectiveness of their relative filter-cake degradation capabilities. Laboratory studies have demonstrated that drill-in fluid filter cake can be effectively removed through the application of a newly developed technique incorporating an enzyme-based polymer degradation system. The data show that through utilization of this newmore » technology, smaller, less costly treatments can be used to treat entire openhole intervals to zero-skin potential with dramatically improved treatment efficiency. Much smaller, lower concentration acid treatments can then be effectively applied to stimulate the interval. Surveys following the field application of the new system have shown not only increased flow, but also flow throughout entire length open- hole intervals.« less