Removal of oil-based drilling fluid (OBM) residue from the wellbore is critical to help prevent costly contamination of clear completion brines. Completion brine contaminated with OBM can adversely affect reservoir producibility. OBM residue may be present as a thin film that coats the casing or as part of the filter cake deposited on the formation. If left in place the oil can contaminate completion brines, cause excessive skin or even create emulsion blockages and formation damage. The best practice is to remove all OBM residue and water wet the casing and reservoir rock. Then clean brines can be maintained, proper zonal isolation through more effective cement bonds can be achieved and skin damage or emulsion blockage can be minimized.
Currently, OBM residue is removed from the wellbore by a series of solvent and surfactant treatments. These treatments result in large disposal volumes of solvents and generally incomplete water wetting of the casing or formation by the surfactant. Eliminating the use of solvents and using only surfactants to effectively remove OBM residue provides a more environmentally-friendly outcome.
A new method for removing OBM residue and water wetting surfaces relies on surfactant nanotechnology in high-density brine to form a micro-emulsion upon contact with oil. OBM filter cake with an acid-degradable weighting agent can also be removed and the reservoir becomes water wet if the surfactant is used in conjunction with an acid precursor. Micro-emulsion technology is also ideal for remediating formation damage by removing emulsion blockages and re-water wetting the reservoir.
This paper presents laboratory data generated during simulated casing cleaning and filter cake degradation experiments. Cleaning efficiency, permeability and wettability studies were performed showing the versatility of micro-emulsion technologies. The paper also presents and discusses field data from completion fluid displacements, cement pre-flushes and filter cake removal operations.