Rotating Magnet Ranging - A New Drilling Guidance Technology

Abstract

Abstract Rotating Magnet Ranging (RMR) employs a permanent magnet in a sub directly behind the drillbit to generate a time varying magnetic field as the bit rotates. This signal is detected by sensors in a nearby well. RMR has been tested in SAGD projects and shown to be capable of correctly positioning new injectors above previously drilled and cased production wells. In these applications, the sensor package is pumped down tubing installed in the producer. The current bit location is evaluated relative to the sensor package along with an estimate of the relative drilling direction. RMR is being used routinely to guide horizontal wells to intersect vertical wells. In this application, the sensor is deployed on a wireline in an uncased interval of the vertical well near the proposed intersection depth. RMR provides steering information to the driller up to 50 meters from the target. Method Figure 1 shows typical RMR geometry. In the drilling well, a permanent magnet housed in a short sub (figure 2- photo) inserted immediately behind the bit generates a magnetic dipole moment, M, which rotates about an axis, s, normal to the bitface. A sensor package (figure 2) in the reference/target well contains a three-component AC magnetometer to measure the time varying magnetic field (H) generated by M. The sensor package also includes a three-component accelerometer and DC magnetometer to measure, respectively, gravity and the Earth's static magnetic field. Ranging data is acquired continuously over a drilling interval, usually the length of a single 9 meter joint of drillpipe. In well intersection applications, the sensor package is typically placed at a fixed depth in the target well. In parallel well applications, such as SAGD, the sensor is periodically repositioned after each drilling interval to keep it adjacent to the next drilling interval.