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System and method for damping vibration in a drill string using a magnetorheological damper

  • US 8,087,476 B2
  • Filed: 03/05/2009
  • Issued: 01/03/2012
  • Est. Priority Date: 03/05/2009
  • Status: Active Grant
First Claim
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1. In a damping system for damping vibration in a down hole portion of a drill string, said damping system comprising a magnetorheological (MR) valve containing an MR fluid subjected to a magnetic field created by at least one coil, said MR fluid flowing through a passage formed in said MR valve, a method of operating said MR valve comprising the steps of:

  • a. energizing said coil of said MR valve for a first period of time so as to create a first magnetic field that alters the viscosity of said MR fluid, said first magnetic field being sufficient to induce a first remnant magnetization in at least one component of said MR valve proximate said passage, said first remnant magnetization being at least about 12,000 Gauss;

    b. substantially de-energizing said coil for a second period of time following said first period of time so as to operate said MR valve using said first remnant magnetization in said at least one component of said MR valve to create a second magnetic field that alters the viscosity of said MR fluid;

    c. subjecting said at least one component of said MR valve to a demagnetization cycle over a third period of time so as to reduce said first remnant magnetization of said at least one component of said MR valve to a second remnant magnetization;

    d. operating said MR valve for a fourth period of time after said demagnetization cycle in step (c).

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