Geometrical instruments – Indicator of direction of force traversing natural media – Borehole direction or inclination
Reexamination Certificate
1998-08-21
2001-11-27
Hirshfeld, Andrew H. (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Borehole direction or inclination
C033S304000, C033S356000
Reexamination Certificate
active
06321456
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a new method for improved surveying of a bore hole using a magnetic survey device. More particularly, this invention relates to a method for determination of the azimuth of a bore hole.
Where magnetic survey instruments are used in the determination of the azimuth of a bore hole, it is the normal practice to relate the magnetic information to the Earth's magnetic field in the determination of the measurement azimuth of the bore hole. The problem is getting accurate magnetic surveys when in close proximity to an adjacent well due to the magnetic interference from magnetic steel components like liners, casing, fish etc., of an adjacent well hole. These components distort the measured magnetic field (TMF(x,y,z)) leading to errors in the calculated azimuth of the bore hole. The magnetic interference field (IB(x,y,z))coming from the adjacent well is derived from a series of magnetic poles of unknown strength and location. If the location of the poles and/or their effect on certain axes of the magnetic instrument were known then the true Earth's field and accurate surveys could be derived. However, it is more common for the magnetism in the adjacent well's tubular not to be known, neither the pole strengths nor their location. In this instance, this new invention allows an improved azimuth of the well being drilled to be derived.
SUMMARY OF THE PRESENT INVENTION
From one aspect, the present invention provides a method that determines where an interference field is at right angles to the well being drilled.
Preferably, this is done by monitoring the total measured magnetic field components in the x and y directions, TMF B(x,y), and determining a maximum value. The value Bz at that position is determined with the expectation that the vertical, or z component, of the interfering field IBz=0 and Bz is not subjected to any interference. The same is true for the TMF B(x,y) minimum value, that is Bz may be determined based on the assumption that IBz=0.
From another aspect, the present invention provides a method for deriving the azimuth of a bore hole comprising the steps of predicting the position where the interference from an adjacent well containing magnetic steel tubular components affects solely the B(x,y) plane or the Bz axis, monitoring the IB(x,y) interference field and/or the IBz interference field to determine the position where B(x,y) and/or Bz are solely affected, calculating at or near one or more of these positions the azimuth of the bore hole by taking measurements of the gravity field along three axes, G(x,y,z) and by taking measurements along three axis B(x,y,z) of the magnetic field. According to the present invention, there is provided a method for surveying a bore hole using a magnetic survey device, comprising the steps of:
monitoring the magnetic field;
resolving an interference constituent of the magnetic field arising from at least one magnetic component contained within an adjacent bore hole;
determining at least one position along the bore hole where either an axial component of the interference constituent in the z-direction IB(z) is at least one of a set of certain values, or where a resultant vector IB(x,y) of axial components of the interference constituent in the x- and y- directions is at least one of said set of certain values; and
measuring the magnetic field at or near to said position; wherein the z-direction is aligned along said bore hole, and wherein when said axial component in the z-direction IB(z) is one of said certain values and/or the resultant vector IB(x,y) is one of said certain values then at least one of said axial component IB(z) or said resultant vector IB(x,y) is zero, whereby said magnetic field may be measured without interference in at least one axis.
The monitoring can be carried out continuously or at regular intervals. Also, it is arranged that the Z axis is preferably along the long axis of the measurement device.
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Conley & Rose & Tayon P.C.
Halliburton Energy Service,s Inc.
Hirshfeld Andrew H.
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