Technical Discussions

The First Use of Gravity Azimuth Drilling in Offshore Drilling

» SPE Paper 87166 (Copyright 2004, IADC/SPE Drilling Conference)

The First Use of Gravity MWDTM in Offshore Drilling Delivers Reliable Azimuth Measurements in Close Proximity to Sources of Magnetic Interference.

Elizabeth Matheson, SPE, ConocoPhillips and Graham McElhinney, SPE, Richard Lee of PathFinder Energy Services.

Abstract

Measurement 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).

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Gravity Azimuth: A New Technique to determine your well path

» IADC/SPE Paper Number 59200 (Copyright 2000, IADC/SPE Drilling Conference)

Gravity Azimuth: A New Technique To Determine Your Well Path

G.A. McElhinney, SPE, PathFinder Energy Services., A. Margeirsson, Jaroboranir hf, Iceland Drilling Co. Ltd., K. Hamlin, SPE and I. Blok, PathFinder Energy Services.

Abstract

Hot Holes with a geothermal gradient over 7 Degrees Fahrenheit per 100ft, high levels of magnetic interference and no returns. In this environment drilling deviated holes to a confined target can tax today’s technology.

This paper describes the use of a new and novel technique that uses the Earth’s Gravity field to determine the direction of a well. Direction from Gravity may normally, not be considered technically possible. However measuring the difference in the spatial position between two sets of accelerometers 30m apart gives the change in azimuth over this interval. These changes accumulate to show the well path trajectory.

The use of the Gravity Azimuth technique may help solve the problems associated with magnetic interference when surveying with magnetic survey instruments. The wider application of this technology into areas with localized magnetic interference, like drilling out of Casing Windows, Multi Well Avoidance, Casing drilling, 3D rotary steering devices and Multi Laterals is discussed. The paper compares the Gravity results to Gyroscopic and Magnetic instruments and discusses the operational consequences of the different methods.