Shale Stabilization with Drilling Fluids Oil Based Muds

The hydratable, dispersible, and brittle shales are all sensitive to water. Instability can be partially eliminated by preventing the water in the drilling fluid from contacting the shale. One solution is to use an oil-based fluid where water is emulsified in the continuous oil phase.

The interfacial film surrounding the emulsified water droplets in an oil mud can act as a semipermeable membrane and provide a mechanism for osmosis. Osmosis is the flow of water from a less concentrated salt solution into a more concentrated solution through a semi-permeable membrane. Water will migrate from the oil mud into the shale when the salinity of the water phase of the oil mud is lower than the salinity of the water phase of the shale. There is evidence that dehydration of the shale occurs when the reverse is true. No migration occurs when the salinities are equal.

Although maximum shale inhibition is realized with oil muds, their use in some wells may not be considered practical because of other factors. These factors must be carefully evaluated in relation to the severity of the shale instability problem. Oil muds can:

  • Reduce the penetration rate in some formations
  • Limit the logging program
  • Affect cuttings analysis
  • Require special preparation and maintenance programs
  • Be environmentally unacceptable
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Responses

  • Hagos
    What is shale stabilization?
    2 years ago

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