U.S. patent application number 11/385159 was filed with the patent office on 2007-09-27 for methods of range selection for positioning marine seismic equipment.
Invention is credited to Leendert Combee, Svein Arne Frivik.
Application Number | 20070223308 11/385159 |
Document ID | / |
Family ID | 38008801 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070223308 |
Kind Code |
A1 |
Frivik; Svein Arne ; et
al. |
September 27, 2007 |
Methods of range selection for positioning marine seismic
equipment
Abstract
A method for selecting a signal arrival for determining an
accurate position of seismic equipment includes the steps of
transmitting a signal from a pinger; predicting a direct arrival
and a reflected arrival of the signal at a receiver, wherein each
arrival is the time between the transmission of the signal to
reception of the signal; measuring arrivals of the signal at the
receiver; selecting the measured signal arrival that is similar to
the predicted direct arrival as a preliminary signal arrival;
defining a confidence interval for the actual direct arrival of the
signal based on the predicted direct arrival and the predicted
reflected arrival; and finalizing the signal arrival, wherein the
selected preliminary signal arrival is the finalized signal arrival
if it is within the confidence interval.
Inventors: |
Frivik; Svein Arne; (Oslo,
NO) ; Combee; Leendert; (Oslo, NO) |
Correspondence
Address: |
WESTERNGECO L.L.C.
10001 RICHMOND AVENUE
(P.O. BOX 2469, HOUSTON, TX 77252-2469, U.S.A.)
HOUSTON
TX
77042
US
|
Family ID: |
38008801 |
Appl. No.: |
11/385159 |
Filed: |
March 21, 2006 |
Current U.S.
Class: |
367/19 |
Current CPC
Class: |
G01V 1/3835 20130101;
G01S 5/26 20130101; G01V 1/38 20130101 |
Class at
Publication: |
367/019 |
International
Class: |
G01V 1/38 20060101
G01V001/38 |
Claims
1. A method for selecting a signal arrival for determining an
accurate position of seismic equipment, the method comprising the
steps of: transmitting a signal from a pinger; measuring arrivals
of the signal at a receiver, wherein each arrival is the time
betveen the transmission of the signal to reception of the signal;
selecting one of the signal arrivals as a preliminary signal
arrival; calculating a confidence interval for an estimated direct
arrival of the signal; and selecting a final signal arrival,
wherein the selected preliminary signal arrival is the selected
final signal arrival if it is within the confidence interval.
2. The method of claim 1, wherein the step of selecting a final
signal arrival further includes: conditioning the selected
preliminary signal arrival to substantially equal the estimated
direct signal arrival at the receiver when the selected preliminary
arrival is not within the confidence interval.
3. The method of claim 1, wherein the estimated direct signal
arrival is calculated as an arrival of the signal without being
reflected off a boundary.
4. The method of claim 3, wherein the estimated directed signal
arrival is calculated based on the pinger-receiver geometry and a
sound speed profile of the medium in which the pinger and receiver
are provided.
5. The method of claim 1, further including the step of determining
the position of the receiver relative to the pinger based on the
selected final signal arrival.
6. The method of claim 2, wherein the estimated direct signal
arrival is calculated as an arrival of the signal without being
reflected off a boundary.
7. The method of claim 6, further including the step of determining
the position of the receiver relative to the pinger based on the
selected final signal arrival.
8. A method for selecting a signal arrival for determining an
accurate position of seismic equipment, the method comprising the
steps of: transmitting a signal from a pinger; predicting a direct
arrival and a reflected arrival of the signal at a receiver,
wherein each arrival is the time between the transmission of the
signal to reception of the signal; measuring arrivals of the signal
at the receiver; selecting the measured signal arrival that is
similar to the predicted direct arrival as a preliminary signal
arrival; and finalizing the selected signal arrival, wherein the
selected preliminary signal arrival is the finalized signal arrival
if it correlates with the predicted direct arrival.
9. The method of claim 8, wherein the pinger and the receiver are
provided in a marine environment.
10. The method of claim 8, wherein the step of finalizing includes
the step of adjusting the selected preliminary signal arrival to
substantially match the predicted direct arrival.
11. The method of claim 8, further including the step of
determining the position of the receiver relative to the pinger
based on the finalized signal arrival.
12. The method of claim 9, further including the step of
determining the position of the receiver relative to the pinger
based on the finalized signal arrival.
13. The method of claim 10, further including the step of
determining the position of the receiver relative to the pinger
based on the finalized signal arrival.
14. The method of claim 13, wherein the pinger and the receiver are
provided in a marine environment.
15. A method for selecting a signal arrival for determining an
accurate position of seismic equipment, the method comprising the
steps of: transmitting a signal from a pinger; predicting a direct
arrival and a reflected arrival of the signal at a receiver,
wherein each arrival is the time between the transmission of the
signal to reception of the signal; measuring arrivals of the signal
at the receiver; selecting the measured signal arrival that is
similar to the predicted direct arrival as a preliminary signal
arrival; defining a confidence interval for the actual direct
arrival of the signal based on the predicted direct arrival and the
predicted reflected arrival; and finalizing the signal arrival,
wherein the selected preliminary signal arrival is the finalized
signal arrival if it is within the confidence interval.
16. The method of claim 15, further including the step of
determining the position of the receiver relative to the pinger
based on the finalized signal arrival.
17. The method of claim 15, wherein the pinger and the receiver are
provided in a marine environment.
18. The method of claim 15, wherein the step of finalizing the
selected arrival includes the step of adjusting the selected
preliminary arrival to substantially match the predicted direct
arrival when the selected preliminary arrival is not within the
confidence interval.
19. The method of claim 18, further including the step of
determining the position of the receiver relative to the pinger
based on the finalized signal arrival.
20. The method of claim 19, wherein the pinger and the receiver are
provided in a marine environment.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to methods for
determining the position of seismic spreads and more particularly
to a model based range selection method for determining the
geometric configuration and position of seismic equipment in a
seismic spread.
BACKGROUND
[0002] In underwater acoustic navigation of a marine seismic
spread, ranges are measured to determine the geometric relationship
between the seismic equipment and a position of the seismic
equipment and the spread. An accurate range is the travel time of
the direct arrival of a signal from a pinger by a particular
receiver. The direct arrival is the acoustic signal traveling along
the path of shortest travel time in the water column without being
influenced by the reflection from a boundary. Reflections from a
boundary, the sea-surface or sea floor, travel a longer distance
than the direct arrival signals and are therefore subject to a time
delay relative to the direct arrival. Tracking the reflections
rather than the direct arrival signals may deteriorate the acoustic
ranges and may cause the acoustic network solution to deteriorate,
resulting in a deteriorated positioning of the seismic
equipment.
[0003] Historically, the ranges with time delays due to reflections
are filtered to avoid their introduction in the positioning
solution. The traditional methods for "editing" the ranges have
been manual, i.e. by adjusting the range by subtracting the effect
of the reflection or by setting a range to passive. These prior art
methods for editing are manageable for positioning systems that
rely on only a few hundred ranges. However, these prior art methods
fail when the number of ranges increase. For example, WesternGeco's
intrinsic range modulated acoustic ranging system may include more
than 10,000 ranges.
[0004] Therefore, it is a desire to provide a method of selecting
the direct range for accurately positioning marine seismic
equipment that addresses drawbacks of the prior art methods. It is
a further desire to provide a method of range selection that
utilizes information about the seismic spread as well as
environmental parameters to predict direct arrival and reflected
arrival of a signal by a receiver. It is a still further desire to
provide a method for rejecting reflected signals that are received.
It is a still further desire to condition a range based on a
received reflected signal.
SUMMARY OF THE INVENTION
[0005] Accordingly, methods for selecting an accurate signal
arrival by a receiver from a pinger for accurately positioning
seismic equipment are provided. The methods are particularly
adapted for ranging systems such as disclosed in U.S. Pat. No.
5,668,775, which is incorporated herein by reference.
[0006] An embodiment of a method for selecting a signal arrival for
determining an accurate position of seismic equipment includes the
steps of transmitting a signal from a pinger; measuring arrivals of
the signal at a receiver, wherein each arrival is the time between
the transmission of the signal to reception of the signal;
selecting one of the signal arrivals as a preliminary signal
arrival; calculating a confidence interval for an estimated direct
arrival of the signal; and selecting a final signal arrival,
wherein the selected preliminary signal arrival is the selected
final signal arrival if it is within the confidence interval.
[0007] Another embodiment of a method for selecting a signal
arrival for determining an accurate position of seismic equipment
includes the steps of transmitting a signal from a pinger;
predicting a direct arrival and a reflected arrival of the signal
at a receiver, wherein each arrival is the time between the
transmission of the signal to reception of the signal; measuring
arrivals of the signal at the receiver; selecting the measured
signal arrival that is similar to the predicted direct arrival as a
preliminary signal arrival; and finalizing the selected signal
arrival, wherein the selected preliminary signal arrival is the
finalized signal arrival if it correlates with the predicted direct
arrival.
[0008] A further embodiment of a method for selecting a signal
arrival for determining an accurate position of seismic equipment
includes the steps of transmitting a signal from a pinger;
predicting a direct arrival and a reflected arrival of the signal
at a receiver, wherein each arrival is the time between the
transmission of the signal to reception of the signal; measuring
arrivals of the signal at the receiver; selecting the measured
signal arrival that is similar to the predicted direct arrival as a
preliminary signal arrival; defining a confidence interval for the
actual direct arrival of the signal based on the predicted direct
arrival and the predicted reflected arrival; and finalizing the
signal arrival for calculating the receiver position, wherein the
selected preliminary signal arrival is the finalized signal arrival
if it is within the confidence interval.
[0009] The foregoing has outlined the features and technical
advantages of the present invention in order that the detailed
description of the invention that follows may be better understood.
Additional features and advantages of the invention will be
described hereinafter which form the subject of the claims of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing and other features and aspects of the present
invention will be best understood with reference to the following
detailed description of a specific embodiment of the invention,
when read in conjunction with the accompanying drawings,
wherein:
[0011] FIG. 1 is a schematic of an embodiment of a spread seismic
equipment of a ranging system of the present invention illustrating
the propagation paths of an acoustic event; and
[0012] FIG. 2 is a block diagram illustrating an embodiment of a
method of range selection for accurately positioning marine seismic
equipment.
DETAILED DESCRIPTION
[0013] Refer now to the drawings wherein depicted elements are not
necessarily shown to scale and wherein like or similar elements are
designated by the same reference numeral through the several
views.
[0014] FIG. 1 is an illustration of an embodiment of a spread of
seismic equipment of a seismic positioning system of the present
invention, generally designated by the numeral 10, illustrated as a
shallow water geometry in 2D. Seismic spread 10 includes at least
one streamer 12 having at least one pinger 14 and a plurality of
receivers 16. As is well known in the art, a seismic spread
commonly includes multiple streamers 12 each of which includes a
plurality of pingers 14 and receivers 16. The geographic location
of at least one point in the spread is typically known from
convention means, such as a global positioning system. For example,
the geographic location of pinger 14 may be determined by a global
positioning system.
[0015] An acoustic transmitter 14, also referred to as a pinger,
produces an acoustic event that is recorded by the plurality of
receivers 16. Each receiver 16 receives an acoustic signal from
pinger 14 at two different times, a direct wave 18 arrival and a
reflected wave 20 arrival.
[0016] As shown in relation to receiver 16a, pinger 14 creates an
acoustic event. The direct wave 18a is the acoustic event traveling
the shortest distance in the water column without being influenced
by a boundary 21 and provides the desired direct or accurate range
22a for positioning the seismic equipment. In the illustration of
FIG. 1, boundary 21 is the seafloor but may be the water surface.
Reflection 20a travels a longer distance than direct wave 18a and
therefore its arrival at receiver 16a is time delayed. An accurate
range 22a for receiver or hydrophone 16a is determined by the
travel time of direct wave 18a. Thus, it is necessary to detect and
track the arrival of direct wave 18a and not the arrival time of
reflections 20a to determine range 22a.
[0017] An accurate image of the spread of the seismic equipment and
its geographic position is necessary for a proper acoustic network.
In a ranging positioning system 10 independent of water depth 24,
it is desired to range as long as possible to ensure that all
ranges 22 (short and long) make a proper acoustic network.
[0018] Tracking reflection 20 arrivals, rather than direct wave 18
arrivals, may deteriorate acoustic ranges 22 due to the time delay
of the arrival of reflection 20 at a particular receiver 16. This
deterioration or break down in the positioning estimates for the
seismic equipment is most common in shallow water environments, but
also occurs in deeper waters when the seismic spread is towed deep.
In shallow water, typically less than 30 to 40 meters, the ratio of
range 22 length to water depth 24 becomes high (much greater than
10). Thus, the time delay between the arrival of direct wave 18 and
reflection wave 20 becomes smaller as a function of offsets, and
accurate selection of ranges 22 becomes more difficult.
[0019] FIG. 2 is a diagram of an embodiment of a method of
positioning seismic equipment, generally denoted by the numeral 26.
Method 26 is described with reference to FIG. 1, and more
particularly in relation to receiver 16a and pinger 14 for purposes
of simplicity. Method 26 includes: step 28--measuring ranges; step
30--selecting an initial range; step 32--predicting a direct range;
step 34--finalizing range selection; and step 36--determining the
position of the seismic equipment.
[0020] Range prediction step 32 includes estimating the arrival
time of direct wave 18a and reflection 20a at receiver 16a, and the
difference between the arrival times, thereby predicting the direct
range. The predicted direct ranges for each receiver is calculated
using the sound speed profile, pinger-receiver geometry, water
depth, streamer depth, and may include other parameters that may
influence the time delay of the arrival of the reflection. Direct
range prediction model 32 may be a complex propagation model, ray
tracing model or a more simplistic geometrical consideration with
velocity information. The direct predicted range from step 32 may
be utilized in the step of selecting an initial range 30 and/or the
step of finalizing a range selection 34.
[0021] In step 28 an acoustic event is created by pinger 14
propagating direct wave 18a and reflected wave 20, the arrival of
each is measured or recorded at receiver 16a. Thus, at step 28 the
arrival measurements provide at least two possible ranges, a direct
range and a reflected range. In preliminary range selection step
30, the measured arrivals are compared so that the preliminary
direct range may be selected. Results from range prediction model
32 may be utilized to select this preliminary direct range
selection, i.e. arrival of direct wave 18a. The preliminary direct
range selection may be fed into seismic equipment position
determination step 36.
[0022] In the embodiment illustrated in FIG. 2, finalizing the
range selection step 34 is conducted before determining the seismic
equipment position 36. Step 34 includes creating a confidence
interval in which arrival of direct wave 18 is likely to occur at a
receiver 16. The confidence interval may be calculated in direct
range prediction step 32 or may be determined using separate
criteria as an additional check point for selecting the direct
range. The preliminary direct range selected in step 30 for a
receiver may be compared to the calculated confidence interval. If
the preliminary direct range selected correlates with the
confidence interval, the preliminary direct range is finalized and
passed to positioning step 36. If the preliminary direct range
selected does not correlate with the confidence interval, the
preliminary range is deemed bad. If the preliminary direct range is
bad it may be rejected in finalizing step 34 and not passed to
equipment positioning step 36. Alternatively, if the preliminary
direct range is bad the preliminary direct range may be conditioned
and the conditioned range passed to equipment positioning step 36.
The conditioned range may be an estimated arrival of direct wave
18. Desirably, in equipment positioning step 36 a conditioned range
is given less weight than a measured direct wave arrival.
[0023] From the foregoing detailed description of specific
embodiments of the invention, it should be apparent that a method
and system for solving the position of seismic equipment that is
novel has been disclosed. Although specific embodiments of the
invention have been disclosed herein in some detail, this has been
done solely for the purposes of describing various features and
aspects of the invention, and is not intended to be limiting with
respect to the scope of the invention. It is contemplated that
various substitutions, alterations, and/or modifications, including
but not limited to those implementation variations which may have
been suggested herein, may be made to the disclosed embodiments
without departing from the spirit and scope of the invention as
defined by the appended claims which follow.
* * * * *