Performance Of Oil Muds At High Temperatures

This paper presents data on the performance of oil muds at high temperatures and high pressures. Included are data and discussions regarding static densities, circulating densities, thermal stability and stability in corrosive environments. The information on static and circulating densities combines PVT data, recently published methods of computing downhole transient and pseudo-steady state temperature data as functions pseudo-steady state temperature data as functions of circulating rates and geothermal gradients, and recently available rheological properties of oil muds at high temperatures and pressures. Thermal stability of various oil muds are discussed on the basis of theoretical physiochemical behavior of the constituents physiochemical behavior of the constituents as well as on the basis of laboratory aging and rheology data. In addition, data on oil base mud in the presence of hydrogen sulfide and carbon dioxide are presented. The data and analyses indicate that the two basic oil mud types, oil base and invert emulsion, have several distinct differences in performance characteristics at high temperature. It appears that the invert emulsion muds have temperature limits (at least economic) because of thermal degradation of their synthetic organophilic colloids and organic surfactants. Critical degradation may occur in a matter of hours at 500 degrees F. Oil base muds that use certain asphalts for the colloidal material have a higher temperature stability. This is because the asphalt does not degrade, at least up to 540 degrees F. and, because the asphalt is a hydrocarbon, does not need synthetic oil wetting and is in itself an emulsifier, and oil wetting agent and surfactant.