Polymeric Water Based DIF (Drill-in Fluid) Improved Design to Stabilize Complex Wellbores

Abstract

AbstractThe design of a drill-in fluid (DIF) requires an in depth understanding of the reservoir formation characteristics in order to minimize production impairment through processes such as fines migration and clay swelling. This is a, relatively, well understood design process for simple homogenous reservoirs. More complex wells, where shales are exposed in the reservoir section or reservoirs are depleted, may require additional products to maintain wellbore stability and allow the well to be completed. This paper assesses the impact on formation damage from the addition of these wellbore strengthening products.Polymeric water based DIFs contain calcium carbonate bridging particles which can be dissolved with acid, and biopolymers which can be degraded with enzymes. Products used for wellbore strengthening usually include graphitic materials, which are neither acid soluble nor degradable by enzymes. This study evaluated the effect of these addition materials in combination with calcium carbonate through a series of Return Permeability tests to determine their effect on sandstone formations. Return Permeability tests were performed to simulate well operations in a laboratory environment, during which the measure of relative permeability is used to quantify any change in permeability caused when a fluid is applied to a rock sample. For comparison purposes, baseline tests with standard polymeric water based DIFs were initially performed. Subsequently, different additives were incorporated in each system to evaluate their effect on the return permeability.This paper presents the results of an extensive study investigating the effect on return permeability from the addition of graphitic and polymer materials used for wellbore strengthening, using two polymeric water based DIFs. The results show that, under the correct conditions, the addition of these products to the fluid formulation for the enhancement of wellbore stability does not significantly impair the permeability of the formation as had previously been believed.