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Drilling fluid and method for drilling in coal-containing formations

  • US 9,969,920 B2
  • Filed: 11/10/2016
  • Issued: 05/15/2018
  • Est. Priority Date: 08/26/2010
  • Status: Active Grant
First Claim
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1. A method for producing a mixed metal-viscosified drilling fluid comprising an aqueous mixture of bentonite, a mixed metal viscosifier, and calcium sulfate (w/v), the method comprising:

  • mixing water, the bentonite and the mixed metal viscosifier;

    monitoring rheology of the mixed metal-viscosified drilling fluid; and

    ,adding the calcium sulfate in an amount of at least 0.05% (w/v) to the mixed metal-viscosified drilling fluid to avoid adverse rheological changes, wherein the calcium sulfate is added to protect an electrostatic interaction between the bentonite and the mixed metal-viscosifier, thereby maintaining the viscosity of the drilling fluid at a yield point of greater than 10 Pa.

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