Oil Base Mud in High Pressure, High Temperature Wells

Abstract

ABSTRACT ADCO’s experience while drilling the sixth deep Khuff well with water base mud to total depth of 21682 ft and a bottom hole static temperature of 465°F has highlighted mud related problems. The mud has shown gelation, barite sagging, sensitivity to formation water influx and possible instability at densities higher than 122 pcf. These problems were considered in the selection criteria of the drilling fluid for the seventh deep Khuff well which required a drilling fluid density of 110–140 pcf with stable HTHP fluid loss at temperature up to 465°F, capable to tolerate influx of Co2, H2S, and high salinity formation water. Studies on various oil & water base muds were performed in various laboratories including ADCO’s, the Shareholders’ and the mud companies’. The development of stable water base mud was not possible. Oil base mud formulation was developed and has been used. The well has reached its total depth at 20085 ft & a bottom hole temperature of 440°F after facing operational challenges requiring mud weight of 155 pcf to control the well and during which, the OBM choice proved to be a success.