Treatment of Aluminum Sulphate Contamination to Water Base Drilling Fluids

A high density KCl-polymer sulfonate drilling fluid was used to drill the third interval (φ311.2 mm) of the well KS-19. When drilling between 6243 m and 6387 m, the drilling fluid was contaminated by industrial waste water containing aluminum sulphate. The drilling fluid was experiencing rheology increase every day, or abrupt change sometimes. Several changes can be seen of the drilling fluid after being contaminated. First, the φ₆ and φ₃ readings, 10s gel strength and yield of the drilling fluid were increased to higher values, other drilling fluid parameters remained normal. Second, the mud in the suction pit and mud ditches had coarse surface and plenty of pinhole bubbles were trapped in the mud, making the mud flow very slowly. Third, the mud became difficult to pump, the mud pump trembled seriously, and the pump strokes per minute and pump pressure were unstable, changing in wide ranges. Charging pumps had to be used during drilling to pump the mud. To resolve these problems, the mud was circulated when the drill bit was at the casing shoe and the bottom of the hole to adjust its properties. Several measures, such as dilution and displacement, changing of the surface tension of the bubbles, neutralization with high pH value, changing rheology and increasing oil content of the mud, were taken to improve the properties of the mud. Drilling was then resumed and there were only small amount of bubbles found in the suction pit and ditches. Circulation was resumed to normal condition.