Removal of skin damage resulting from internal and external filter cake deposition during oil well reservoir drilling with invert emulsion drill-in fluid is desirable in order to maximize hydrocarbon recovery. Efficient filter cake cleanup is required for a number of open-hole completion operations, including the use of stand-alone and expandable sand screens, and conventional gravel pack applications for both production and water-injection wells.
Most of the currently used chemical methods to remove invert emulsion filter cake and internal formation damage are based on the use of acids, solvents and mutual solvents mixed in clear brine. Completing a well after drill-in with emulsion-based fluids is time-consuming and costly, and usually involves large volume multi-stage soak treatments.
Surfactant technology, when appropriately combined with conventional acid, allows a single-stage invert emulsion cleanup process. In this "one-step" cleanup method, the invert emulsion filter cake is incorporated into the organized surfactant in solution and the acid-soluble particles are then decomposed.
A number of injection permeability tests were performed on Berea sandstone cores and ceramic discs using various invert emulsion drilling fluids for filter cake deposition and organized surfactant in solution/acid blends for filter cake removal. This investigation demonstrated that, when using this technology to destroy the filter cake, (1) the invert emulsion is incorporated into the surfactant solution, (2) the solids become water-wet, (3) sludge formation between the acid and invert emulsion cake is prevented, and (4); and the majority of acid-soluble particles are removed.
This approach appears to be a credible method for removing formation skin damage and increasing hydrocarbon recovery and/or water injection rates.