Study on the Performance of New Ultra-high Temperature High Density Oil Base Mud Thinners

Three thinners, A, B and C have been synthesized to deal with extra viscosity of high temperature high density oil base drilling fluids. Thinner A, a condensation polymerized fatty acid, was obtained by copolymerizing one or more raw materials such as dodecahydroxyl stearic acid, polyhydroxy stearic acid, stearic acid, and the homopolymer of the product of dodecahydroxyl stearic acid and stearic acid with stearic acid. Thinner B was obtained by reacting the product of fatty acid or fat and polyamine at 100℃-200℃ with maleic acid and maleic acid anhydride at 80℃-150℃, and then dispersed the product with 40% oleyl alcohol, fatty acid or condensation polymerized fatty acid. Thinner C was a derivative from the reaction product of condensation polymerized fatty acid, alcohol amine and polyamine. The working mechanisms of these thinners are discussed in this paper. Added poor quality clay to contaminate or added barite to weight a high density (2.2 g/cm³) oil base mud to 2.4 g/cm³, then treated the weighted mud with three thinners to test their ability to reduce viscosity. It was found that the thinner A and the thinner C both were able to control the rheology of mud caused by the addition of poor quality clays within predetermined range, and the oil base mud can thus be reused for many more times, thereby reducing mud cost. The thinner B was able to reduce mud viscosity caused by the addition of barite, hence the pump pressure. The thinner B has thinning efficiency of 77%, and functions properly at 225℃.