Semblance processing for an acoustic measurement-while-drilling system for imaging of formation boundaries
First Claim
1. A downhole tool for determination of the position and orientation of a bed boundary during drilling of a wellbore, comprising:
- (a) a transmitter for transmitting acoustic signals at at least one position in the wellbore during drilling of the wellbore, said acoustic signals having an acoustic velocity;
(b) a plurality of spaced apart receivers for detecting signals transmitted by the transmitter that are reflected by the bed boundary; and
(c) a processor determining semblance of the reflected signals in a slowness domain and determining from said semblance and said acoustic velocity a distance and orientation of the bed boundary relative to the tool.
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Accused Products
Abstract
The present invention provides a system for drilling boreholes having a downhole subassembly which contains an acoustic measurement-while-drilling system. It uses the acoustic velocity through the formations surrounding the borehole and an acoustic transmitter and a set of receivers for determining the bed boundaries surrounding the borehole formation. Semblance of the data is determined in a slowness/intercept-time domain. Coherence and semblance filtering methods are used to differentiate between reflection signals and noise. The position and orientation of the bed boundary relative to the tool are determined. A further processing step uses the relative position and orientation determined for a number of tool positions to further discriminate against noise and obtain an absolute position and depth of the bed boundaries.
69 Citations
18 Claims
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1. A downhole tool for determination of the position and orientation of a bed boundary during drilling of a wellbore, comprising:
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(a) a transmitter for transmitting acoustic signals at at least one position in the wellbore during drilling of the wellbore, said acoustic signals having an acoustic velocity; (b) a plurality of spaced apart receivers for detecting signals transmitted by the transmitter that are reflected by the bed boundary; and (c) a processor determining semblance of the reflected signals in a slowness domain and determining from said semblance and said acoustic velocity a distance and orientation of the bed boundary relative to the tool. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of determining the position of a bed boundary during the drilling of a wellbore, comprising:
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(a) using a transmitter on a downhole tool to transmit acoustic signals at at least one downhole location; (b) using a plurality of spaced apart receivers on the downhole tool to receive acoustic signals reflected by the bed boundary; and (c) using the downhole processor to process the acoustic signals to determine a position and orientation of the bed boundary relative to the downhole tool based upon a semblance of the received signals. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A method of determining the position of a bed boundary during the drilling of a wellbore, comprising:
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(a) using a transmitter on a downhole tool to transmit acoustic signals at a plurality of downhole locations; (b) using a plurality of spaced apart receivers on the downhole tool to receive acoustic signals reflected by the bed boundary at each of said plurality of downhole locations; and (c) using a processor to; (i) determine semblances of the acoustic signals in a slowness/offset-time domain at each of said plurality of downhole locations, (ii) filter the determined semblances to give a set of filtered semblances at each of said plurality of downhole locations, (iii) from said set of filtered semblances and a velocity of the acoustic signals, determine a relative position and orientation of the bed boundary corresponding to each of said plurality of downhole locations, and (iv) determine an absolute position and depth of the boundary from said relative positions and orientations and from supplemental information. - View Dependent Claims (18)
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Specification