The First Use of Gravity MWD in Offshore Drilling Delivers Reliable Azimuth Measurements in Close Proximity to Sources of Magnetic Interference
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The First Use of Gravity MWD in Offshore Drilling Delivers Reliable Azimuth Measurements in Close Proximity to Sources of Magnetic Interference Elizabeth Matheson; Elizabeth Matheson ConocoPhillips Search for other works by this author on: This Site Google Scholar Graham McElhinney; Graham McElhinney PathFinder Energy Services Search for other works by this author on: This Site Google Scholar Richard Lee Richard Lee PathFinder Energy Services Search for other works by this author on: This Site Google Scholar Paper presented at the IADC/SPE Drilling Conference, Dallas, Texas, March 2004. Paper Number: SPE-87166-MS https://doi.org/10.2118/87166-MS Published: March 02 2004 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Matheson, Elizabeth, McElhinney, Graham, and Richard Lee. "The First Use of Gravity MWD in Offshore Drilling Delivers Reliable Azimuth Measurements in Close Proximity to Sources of Magnetic Interference." Paper presented at the IADC/SPE Drilling Conference, Dallas, Texas, March 2004. doi: https://doi.org/10.2118/87166-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE/IADC Drilling Conference and Exhibition Search Advanced Search AbstractMeasurement While Drilling (MWD) is the preferred method of surveying a well bore when drilling deviated wells. MWD has an advantage over other types of surveying in that the tools are part of the Bottom Hole Assembly (BHA) and surveys can be obtained quickly without the need for interrupting the drilling operation to run a separate surveying tool. However, like all magnetic survey instruments, MWD is susceptible to magnetic interference. The directional azimuth information becomes unreliable when in close proximity to sources of magnetic interference such as casing strings or adjacent wells.This paper describes a new method of MWD surveying which includes a second accelerometer sensor package to derive azimuth rather than using magnetometers. It is therefore not prone to magnetic interference and the same drawbacks as conventional MWD. The technique uses the inherent bending of a BHA between the two sets of accelerometers in order to measure the relative change in azimuth.Two case histories are outlined where this technique was successfully used to sidetrack two near vertical wells from directly below existing casing strings despite the presence of magnetic interference. In both cases, the ability to initiate the build as early as possible was important as it provided the greatest possible chance of achieving the relatively tight directional plan. The use of Gravity MWD may provide considerable cost savings compared to alternative techniques that could incur additional rig time, be sensitive to movement and may not be capable of including real time Logging While Drilling (LWD).IntroductionThis paper aims to explain the theory behind the Gravity MWD technique and show how it has been incorporated into existing MWD technology.It describes how the technique was used successfully in two UKCS Southern North Sea wells. Both wells were sidetracks of existing wells where the directional plan needed to be initiated as early as possible in order to ensure the relatively tight well path was achieved. The use of conventional MWD systems would have been limited in both these wells due to the influence of magnetic interference resulting from the proximity to the casing strings rendering the measured well bore azimuth unreliable. The standard alternative to Gravity MWD would have been the use of gyro technologies, however there are drawbacks associated with using a gyro. The operational procedures are described, and issues relating to the novelty of the technique are discussed.The results from both wells are presented in order to highlight the strengths of the technique and also the limitations. Comparisons are made between the data derived using the Gravity MWD technique and that obtained from the standard MWD magnetometer azimuths.Theory of the Gravity MWD TechniqueConventional MWD systems utilise a single tri-axial magnetometer sensor to measure the individual components of the Earths magnetic field and a single tri-axial accelerometer sensor to measure the individual components of the Earths gravity field. The vector components of these forces can then be resolved in order to obtain directional information (i.e. inclination, azimuth and tool face) relating to the orientation of the MWD tool and hence the well path.MWD tools, like all magnetic survey instruments, rely on the magnetometer package as the primary sensor for measuring wellbore direction or azimuth. However the azimuth reading becomes unreliable when subjected to external sources of magnetism. In the drilling environment this magnetic interference can occur as a result of close proximity to casing strings, nearby wells or steel components in the BHA. In contrast, the Gravity MWD technique incorporates the use of a second tri-axial accelerometer package in order to derive a Gravity MWD Azimuth value by simultaneously measuring the Earths gravity field at two separate points. As this method does not use the magnetometer sensors to measure azimuth it is therefore not affected by the usual limitations of magnetic interference. Keywords: magnetic field, gravity mwd survey, inclination, mwd technique, tool string, azimuth, directional sensor, drill collar, gravity mwd azimuth, accelerometer Subjects: Well Planning, Drilling Operations, Trajectory design This content is only available via PDF. 2004. IADC/SPE Drilling Conference You can access this article if you purchase or spend a download.
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