Development of New Kill Fluids with Minimum Sagging Problems for High Pressure Jilh Formation in Saudi Arabia

Abstract

Abstract A successful kill fluid formulation for the overpressured Jilh formation has been achieved. Jilh formation is a dolomitic middle Triassic tight zone that ranges from 8,000 to 10,000 ft TVD with abnormal salt-water pressure that requires a kill fluid with a density up to 150 lb/ft3 (pcf). Addition of weighting materials such as barite (BaSO4) or hematite (Fe2O3) is needed to achieve the desired density for the kill fluid. However, maintaining high volume of solid content for barite particles (or any other weighting material) in suspension is challenging, especially for extended period of time. This phenomenon is described in the industry as static barite sag and it may lead to serious well control incidents and lost circulation. Saudi Aramco developed a new formula for kill fluids at high range of densities up to 150 pcf using barite with manganese tetroxide (Mn3O4). No similar formulations were developed before to the best of the authors' knowledge. The properties of small particle size (D50=1 μm), spherical shape, and high specific gravity (4.95 g/cm3) of manganese tetroxide make it a good weighting material to reduce solids loading and settling compared to barite (SG= 4.20 g/cm3 and D50=20 μm). Results show that the density variation between the upper and lower section after 24 hours of vertical static condition is 5 pcf for the new formula (density= 150 pcf) compared to a variation of 13 pcf for the conventional formula that has barite only. When the drilling fluid is put in inclined static condition for 24 hours, the density variation is 6 pcf for the new formula (density= 150 pcf). However, the conventional formula showed a density variation of 17 pcf. The experimental work in this paper involved rheological properties, thermal stability, HT/HP filtration, and static sagging. This paper also describes field cases with barite sagging in high temperature wells and method and formulation of combining manganese tetroxide and barite to formulate new kill fluid formulations for Jilh Formation in Saudi Arabia fields.