FUNDAMENTALS OF SHALE STABILIZATION - WATER TRANSPORT THROUGH SHALES

One area where water-based muds need improved performance is in shale inhibition. However, before existing mud systems can be improved, the mechanisms by which water invades shales and how present-day inhibitiv e additives operate must be fully understood. An experimental techniqu e has been developed that uses radioactive tracers to monitor the prog ress of water and selected dissolved ions through a shale core plug. B y varying experimental parameters, such as water composition and appli ed pressure drop, the dominant mechanisms by which water is transporte d through shales have been identified. Under conditions of zero applie d pressure, diffusion processes control water and ion movement through shales. Concentration gradients are the driving force for mass transf er of ionic species through shales. We observed no evidence to indicat e that osmosis caused mass transfer of water. Applied pressure caused an increase in water and ion transport rates. Above a threshold pressu re, water and dissolved ions travel at the same rate irrespective of t he ion concentration.