Oil-phase drilling muds are widely employed in the Anadarko Basin where they offer improved temperature stability and drilling efficiency in these hot, geopressured zones.
Diesel/mutual solvent remedial treatments have been used in the Anadarko wells to remove oil-phase mud from the wellbore area and fractures. These treatments reduce the mud viscosity in a reversible manner such that subsequent exposure of the mud to water can cause an increase in mud viscosity and potential plugging of the well. The diesel/mutual solvent leaves the exposed zone in an oil-wet state which can lower the productive capacity of the well. In addition, the diesel/mutual solvent treatments are expensive and particularly hazardous at the high surface treating pressures encountered.
A laboratory investigation was performed in which alternative mud removal systems were tested. An Aqueous-Based Cleanup System has been developed to remove oil-phase muds following drilling. The system incorporates 2% KCl with an organic solvent and a surfactant blend. The treatment irreversibly reduces oil-phase mud viscosity while suspending mud solids for removal from the reservoir. The Aqueous-Based Cleanup System restores the mud-damaged zone to a water-wet state for maximum hydrocarbon productivity. This system offers a less expensive and safer alternative to the diesel/mutual solvent treatments.
This paper presents laboratory data comparing the effects of several mud removal systems on oil-phase muds and their associated wetting tendencies. Anadarko Basin case histories of Aqueous-Based Cleanup System treatments are presented. Significant production increases were achieved with the treatments.