Rate gyro wells survey system including nulling system
DCFirst Claim
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1. A method of performing a survey of a well borehole comprising the steps of:
- (a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°
of housing rotation, and(i) a first output indicative of north comprises N measurements is determined at said first sonde position,(ii) said housing is then rotated by 180° and
a second output indicative of north comprising another N measurements is determined at said second sonde position, and(iii) N is an integer;
(b) combining said first and second outputs indicative of north to yield a measure of north in which systematic instrument error is reduced;
(c) positioning the sonde at spaced locations along a well borehole; and
(d) repeating step a) at each said spaced location.
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Abstract
A method for well borehole survey is set out. A sonde supports X and Y accelerometers and X and & sensors on a rate gyro having a Z axis aligned with the sonde. On a slickline, or within a drill string, the sonde is used to measure four variables, these being Gx and Gy, Ax and Az. This enables well azimuth and inclination to determined. Measuring depth enables a survey to be made.
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Citations
60 Claims
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1. A method of performing a survey of a well borehole comprising the steps of:
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(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°
of housing rotation, and(i) a first output indicative of north comprises N measurements is determined at said first sonde position, (ii) said housing is then rotated by 180° and
a second output indicative of north comprising another N measurements is determined at said second sonde position, and(iii) N is an integer; (b) combining said first and second outputs indicative of north to yield a measure of north in which systematic instrument error is reduced; (c) positioning the sonde at spaced locations along a well borehole; and (d) repeating step a) at each said spaced location. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of obtaining a survey in a well borehole subject to deviation from the vertical which comprises the steps of:
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(a) positioning in a well borehole a rate gyro having an axis of rotation coincident with the major axis of a sonde which supports said rate gyro; (b) moving said sonde along the well borehole and making two orthogonal signal measurements at spaced locations; (c) combining said two orthogonal signals measurements to obtain a reference north measurement; (d) reducing systematic instrument error ill said orthogonal signal measurements by making measurements differing by 180°
;(e) measuring the direction of gravity along the sonde during movement in the well borehole by making an additional two orthogonal signal measurement; and (f) determining from said additional two orthogonal measurements at least two dimensions of the position of the sonde in the well borehole. - View Dependent Claims (12, 13, 14, 15)
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16. A method of performing a survey of a well borehole comprising the steps of:
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(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°
of housing rotation, and(b) making a first gyro measurement indicative of north; (c) moving said gyro and making second, third and fourth measurements indicative of north and wherein (i) said first and said third measurements arc at 180°
;(ii) said second and said fourth measurements are at 180°
; and(iii) said measurements are made after 90°
rotation;(d) summing said measurements indicative of north to yield a measure of north; (e) reducing instrument error in said summation of north by combining said measurements; (f) moving said sonde between spaced locations along a well borehole; and (g) repeating steps (b)-(e) at each said spaced location. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24)
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25. A method for measuring the position of a survey sonde in a well borehole, comprising the steps of:
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(a) positioning a rate gyro in a well survey sonde; (b) moving the sonde to a survey position in the well borehole; (c) making a first and a second gyro reading at that survey position, wherein said first and second gyro readings provide information useful in determining north; (d) positioning a pair of accelerometers at right angles in said sonde wherein one accelerometer is located in a plane at right angles to the major axis of said sonde; (e) moving the sonde to a second survey position along the well borehole; (f) making accelerometer measurements as the sonde moves along the well borehole; and (g) determining from said gyro measurements and said accelerometer measurements the path of the well borehole in the earth. - View Dependent Claims (26, 27, 28, 29, 30, 31)
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32. A method of performing a survey of a well borehole comprising the steps of:
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(a) positioning within a well borehole an elongate sonde having a rate gyro therein rotating about an axis and forming an output indicative of north, wherein said rate gyro is supported by a housing rotatable between first and second positions separated by 180°
of housing rotation, and wherein power to operate components within said sonde is supplied by a power supply within said sonde, and(i) a first output indicative of north comprises N measurements is determined with said gyro in said first position, (ii) said housing is then rotated by 180° and
a second output indicative of north comprising another N measurements is determined with said gyro in said second position, and(iii) N is an integer; and (b) combining said first and second outputs indicative of north to yield a measure of north which contains reduced systematic instrument error. - View Dependent Claims (33, 34, 35, 36, 37, 38)
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39. A method of obtaining a survey in a well borehole, comprising the steps of:
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(a) positioning in a well borehole a rate gyro; (b) obtaining direction measurements X, Y, -X and -Y from the response of said rate gyro, wherein X and -X differ by 180° and
Y and -Y differ by 180°
;(c) obtaining a reference direction measurement from said direction measurements; and (d) combining pairs of said direction measurements to reduce systematic instrument error in said reference direction measurement. - View Dependent Claims (40, 41, 42, 43, 44)
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45. A method for obtaining the orientation of a sonde within a well borehole, comprises the steps of:
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(a) positioning a rate gyro having at least one axis within said sonde; (b) with said gyro, making at least two orthogonal signal measurements at at least one location within said well borehole; (c) obtaining a measure of true north from said two orthogonal signal measurements; (d) measuring the direction of gravity at said at least one location within said well borehole; and (e) determining from said at least two orthogonal signal measurements and said measure of gravity the azimuthal orientation of said sonde within said well borehole. - View Dependent Claims (46, 47, 48, 49, 50, 51, 52)
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53. An apparatus for measuring a sequence of data from within a well borehole, comprising;
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(a) a sonde which is conveyed within said borehole, wherein said sonde comprises (i) a rate gyro comprising at least one axis, (ii) a power supply to operate said rate gyro, (iii) a memory for recording response of said rate gyro, and (iv) means for measuring the direction of gravity acting upon said sonde; (b) a CPU for (i) combining a first and a second measurement from said rate gyro to obtain a measure of true north, (ii) combining a third and a fourth measurement from said rate gyro with said first and second measurements to reduce systematic instrument error in said measure of true north; and (iii) combining said measure of gravity direction and said measure of true north to obtain said measured sequence of data; and (c) means for conveying said sonde within said well borehole. - View Dependent Claims (54, 55, 56, 57, 58, 59, 60)
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Specification