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Methods for evaluating borehole volume changes while drilling

  • US 9,404,327 B2
  • Filed: 08/14/2012
  • Issued: 08/02/2016
  • Est. Priority Date: 08/26/2011
  • Status: Active Grant
First Claim
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1. A method for identifying a borehole washout event while drilling a subterranean wellbore, the method comprising:

  • (a) pumping drilling fluid through a drill string located in a subterranean wellbore, the drill string including a plurality of axially spaced along string pressure sensors, said pumping operative to create a downstream flow rate in the drill string and an upstream flow rate in an annulus external to the drill string;

    (b) rotating a drill bit deployed on an end of the drill string, said rotating operative to drill the subterranean wellbore;

    (c) using the plurality of along string pressure sensors to make a corresponding plurality of subsurface annular pressure measurements at a corresponding plurality of measured depths while drilling in (a) and (b);

    (d) transmitting the plurality of pressure measurements to a processor;

    (e) causing the processor to process the plurality of measurements made in (c) to compute a plurality of annular interval densities;

    (f) monitoring the plurality of annular interval densities computed in (e) with time while drilling in (a) and (b); and

    (g) evaluating (i) a decrease in at least one of the annular interval densities and a substantially constant differential flow rate between the downstream and upstream flow rates as an indicator of the borehole washout and (ii) evaluating a decrease in a measured annular interval static density obtained by removing annular friction effects from the measured annular interval circulating density below a modeled annular interval static density as a further indicator of the borehole washout.

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