Patent ID: 8462012
Filing Date: 2013-06-11
Classification: E21B

Abstract:
1. A method comprising: drilling a new well in a field having an existing cased well using a bottom hole assembly having a drill collar having by an insulated gap; generating a current on the bottom hole assembly such that some of the current passes through a surrounding formation and travels along a casing of the existing cased well; measuring from the bottom hole assembly a magnetic field caused by the current traveling along the casing, of the existing cased well to determine a measurement of the magnetic field; adjusting a trajectory of the bottom hole assembly to avoid a collision between the new well and the existing cased well based on the measurement of the magnetic field; and estimating a relative position of the new well to the existing cased well based on the measurement of the magnetic field; wherein the relative position of the new well to the existing cased well is estimated based on the measurement of the magnetic field and a probability distribution of a probable location for the bottom hole assembly based on survey data.