Abstract:

The hydration swelling of shale may cause to or intensify the mechanics unbalance of borehole. The hydration swelling pressure of shale should be studied when studying borehole instability problems. But, it is quite difficult to measure it directly. This paper presents that the hydration swelling pressure of shale is the repel force betweem clay particles caused by osmotic hydration of clay minerals and provides a theoretic method to calculate the swelling pressure of shale using mineralogical parameters according to double layer theory. These parameters include the specific surface of clay fraction, the specific charge of clay, the ions concentration in the pore fluid specimen after swelling test, the valence of the counter-ions and the half distance between the clay plates in the specimen. This paper shows particularly the calculation steps and the ways to get these parameters and an example.

Key words: Hydrate control, Hydrochemistry, Clay swelling, Clay stabilization, Hole sloughing prevention, Hole stabilization