Ability to identify casing collars in real-time is critically important for whipstock casing exit operations, because milling through casing collars could cause significant loss in rig time, excessive damage and even failure of downhole equipment, and potential blockage of the exit window by casing collar spinning. Running wireline to identify casing collars is the typical solution to address the challenge, but incurs additional rig time and cost. This paper present a new technology to locate casing collars in real time with Gamma Ray density measurement, deployed on drill pipe, eliminating the need for a dedicated wireline run. Multiple case histories of field testing the technology in North Sea, covering a wide range of casing sizes from 7-in and 18 5/8-in, are presented as well.
The Gamma Ray density measurement is used for identifying casing collars by detecting the differences in density readings between collar and casing. Gamma rays are continuously emitted from a nuclear source as the density tool moves in the wellbore, and the readings of the near and far detectors, after signal travels through and interacts with casing and formation, are interpreted to calculate density. Density readings are transmitted to surface in real-time through mud-pulse telemetry and are processed to visualize casing collar locations in a log.
The new technology was successfully field tested in North Sea in multiple wells covering a wide range of casing sizes, from 7-in up to 18 5/8-in, with different depths and inclinations. The operational processes and results from the field tests are discussed in this paper. The casing collars were successfully located in each field test, proving the robustness of the technology over a broad range of application parameters. It was discovered from the field tests that the bottomhole assembly (BHA) configuration, tool orientation, tool string rotational speed, sensor standoff and logging speed are critical to clearly identifying casing collars.
This paper presents a new method of using the drill pipe deployed Gamma Ray density measurement to detect casing collars in real-time to optimize whipstock placement for improved reliability and efficiency of casing exit operations. It also provides the best practices of applying the technology in a wide range of well and casing configurations.