Investigating the Corrosivity of KCl/Polymer Drilling Mud on Downhole material

Abstract

The corrosive effect of drilling fluids was analysed by testing the corrosivity of a KCl/Polymer formulation, with temperature and salt concentration as the measurement variables. This was carried out using the weight loss technique in order to measure the effect of KCl/polymer muds on carbon steel, testing the mud behaviour for three different temperatures and the salt concentrations these helps in knowing the behaviour of the mud on downhole materials. From the Experiment it was confirmed that drilling fluids are corrosive and with the presence of salt and temperature, the corrosivity increases but decreases with increase in salt concentration. The rise in corrositivity continues with increasing temperature, but with the retardation in oxygen solubility the rise ceases. The corrosion rate of KCl/Polymer mud with these variables indicated high corrosion rate, which could be effect of other parameters that aided conductivity and the effect of temperature in the process. Those could have been based on the additives used in the mud that also contributed in aiding corrosion. However these effects were not regarded as prominent due to the addition of caustic soda that gave the mud a reasonably high pH of 9.5 to 10, which also inhibits corrosion. Other factors such as oxygen, whose effect was controlled by temperature, could have contributed to the corrosion rate. A low weight loss was shown after 72 hours exposure of the specimen to the mud. This was anticipated to be the inhibiting nature of potassium chloride, the static nature of the mud based on zero shear stress effect on the carbon steel surface and less oxygen transportation to the corroding specimen due to zero agitation of the mud. The minimum corrosion rate of the mud was 0.32 mm/year which was at the highest salt concentration and the lowest temperature of 40 0 C. The maximum corrosion rate was 0.96 mm/year which was at the lowest salt concentration and the highest temperature of 80 0 C, this agrees in principle with the behaviour of temperature and salt concentration.