Abstract:

Activity equilibrium theory was presented long ago and applied to evaluate and design of anti-sag property of mud filtrate. However, since it is impossible to take water sample from shale formation, so far we haven' t found a way to determine the ionic activity of water solution in shale formation through laboratory experiment. Therefore, its application in shale formation had always been restricted. In this paper, a theoretical research is made on the application of geophysical logging in this domain. The results show that it is possible to determine the ratio of mud filtrate to the ionic activity of formation water solution and the iomic activity by making fukk use of the present log data combining with the dual water model of shaly sand formation. Accordingly, anti-sag property of mud filtrate can be adjusted, or the bydration of mudrock can bi conteoled.

Key words: Formation water, Formation damage prevention, Drilling fluid filtrate, Hole sloughing prevention, Shale control