NO347442B1 - A seismic sensor unit, a system for seismic surveying and a method for processing seismic data - Google Patents

Description

BACKGROUND

The following descriptions and examples do not constitute an admission as prior art by virtue of their inclusion within this section.

Seismic exploration involves surveying subterranean geological formations for hydrocarbon deposits. A seismic survey may involve deploying a seismic source and a seismic sensor at predetermined locations. The source generates seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formations typically scatter the seismic waves, changing their direction of propagation and other properties. Some of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes, others to particle motion, and industrial surveys deploy one or more of these types of sensors. In response to detected seismic events, these sensors generate electrical signals to produce seismic data. Analysis of seismic data can indicate a presence or absence of probable locations of hydrocarbon deposits.

The patent literature includes several publications which relates to seismic exploration, seismic sensors and analysis of seismic survey data. The international patent application WO 2014/164803 A2 discloses an internal bend restrictor for opto/electrical armoured cables used for seismic surveys. An ocean bottom cable (OBC) comprising a plurality of sensor nodes for collecting seismic data may be deployed to and retrieved from an ocean bottom during seismic operations using a winch. Such deployment and retrieval operations may exert substantial stress on the OBC at an interface between the sensor nodes and cable segments of the OBC. A reinforcement sleeve is provided to reduce the mechanical stress at such interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of various techniques are described hereafter with reference to the accompanying drawings. It should be understood, however, that the accompanying drawings illustrate various implementations described herein and are not meant to limit the scope of various techniques described herein.

Figure 1 illustrates a device for acquiring seismic survey data in accordance with implementations of various techniques described herein.

Figure 2 illustrates a block diagram of a device for acquiring seismic survey data in accordance with implementations of various techniques described herein.

Figures 3A-3B illustrate deployment of a device for acquiring seismic survey data in accordance with implementations of various techniques described herein.

Figures 4A-4D illustrate various sensor arrangements of a device for acquiring seismic survey data in accordance with implementations of various techniques described herein.

Figure 5 illustrates a method for acquiring seismic survey data in accordance with various implementations described herein.

SUMMARY

Various implementations described herein are directed to a seismic sensor device, which includes a housing and at least two pressure sensors coupled to the housing that are spaced apart by a separation distance. The difference in pressure signals between the at least two pressure sensors is configured to be used to reconstruct pressure signals at locations other than where the at least two pressure sensors are located.

Various implementations described herein are also directed to a seismic sensor device, which includes a housing that is connected to at least a first portion of a cable, wherein the housing extends parallel to a direction that the portion of the cable extends; and at least two pressure sensors coupled to the housing that are spaced apart by a separation distance along the direction in which the first portion of the cable extends.

Various implementations described herein are also directed to a system, which includes an ocean bottom cable and a plurality of sensor units disposed along the ocean bottom cable. Each sensor unit is spaced apart by a first separation distance. Each sensor unit includes at least two pressure sensors spaced apart by a second separation distance. The difference in pressure signals between the at least two pressure sensors is configured to be used to reconstruct pressure signals at locations between the plurality of sensor units.

Various implementations described herein are also directed to a method for processing seismic data, which includes receiving seismic data that had been acquired using sensor units disposed along an ocean bottom cable. Each sensor unit includes at least two pressure sensors that are spaced apart by a first separation distance. The method further includes calculating a difference in pressure signals between the at least two pressure sensors to obtain pressure signals at locations between the sensor units.

The above referenced summary section is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section. The summary is not intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted in any part of this disclosure.

Indeed, the systems, methods, processing procedures, techniques, and workflows disclosed herein may complement or replace conventional methods for identifying, isolating, or processing various aspects of seismic signals or other data that is collected from a subsurface region or other multi-dimensional space, including time-lapse seismic data collected in a plurality of surveys.

DETAILED DESCRIPTION

The discussion below is directed to certain specific implementations. It is to be understood that the discussion below is only for the purpose of enabling a person with ordinary skill in the art to make and use any subject matter defined now or later by the patent “claims” found in any issued patent herein.

It is specifically intended that the claimed invention not be limited to the implementations and illustrations contained herein, but include modified forms of those implementations including portions of the implementations and combinations of elements of different implementations as come within the scope of the following claims. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with systemrelated and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. Nothing in this application is considered critical or essential to the claimed invention unless explicitly indicated as being "critical" or "essential."

It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first object or step could be termed a second object or step, and, similarly, a second object or step could be termed a first object or step, without departing from the scope of the invention. The first object or step, and the second object or step, are both objects or steps, respectively, but they are not to be considered a same object or step.

In marine seabed seismic exploration with cables, where the cable either contains the seismic sensors or where the sensors are connected in other ways to a cable, such as having nodes connected to a main cable by way of secondary cables (known as nodes on a rope), ease of handing is a feature of interest. Another consideration in commercial cable seabed surveys relates to cost, which is affected by ease of handling and deployment. Different configurations and features of sensors and cables can have an effect on the commercial viability of a seabed survey. Also, the robustness of a design can help to reduce downtime due to failure of equipment and therefore also help improve the viability of a commercially successful survey.

With that in mind, the present disclosure relates to a number of combinations of embodies features that include advantageous designs of methods and equipment for seabed seismic surveys.

The following paragraphs describe various techniques for acquiring seismic survey data, which will now be described with reference to Figures 1-5.

Figure 1 illustrates a diagram of a device 100 for acquiring seismic survey data in accordance with implementations of various techniques described herein.

In some implementations, the device 100 may be coupled to a cable, such as, e.g., an ocean bottom cable (OBC), and as such, the device 100 may be configured to rest on a seabed or sea floor. In other implementations, the device 100 may be embodied as a stand-alone unit that is configured to rest on a seabed or sea floor. As such, the device 100 may be referred to as a seismic survey device. These features of the device 100 are described in greater detail herein.

The device 100 may include a housing 104, which may be referred to as sensor housing, case, or other container. In various implementations, the housing 104 may be contoured to have a geometric shape. For instance, as shown in Figure 1, the housing 104 may be in form of a cylinder having a cylindrical contour or shape.

The device 100 may include a plurality of sensors, such as, e.g., various types of seismic sensors, coupled to the housing 104. For instance, the sensors may include one or more particle motion sensors, such as, e.g., geophones and/or accelerometers, and/or multiple pressure sensors, such as, e.g., hydrophones. As shown in Figure 1, the multiple pressure sensors may include at least two separate hydrophones, such as a first hydrophone H1 and a second hydrophone H2. Further, as shown, the multiple pressure sensors (e.g., first and second hydrophones H1, H2) may be spaced apart by a separation distance 108. The multiple pressure sensors (e.g., first and second hydrophones H1, H2) may be configured to acquire seismic survey data and calculate pressure gradients in multiple directions, including multiple horizontal directions.

The multiple pressure sensors (e.g., first and second hydrophones H1, H2) may be configured to separately record the seismic survey data for calculating differences between sensed pressure gradients. The multiple pressure sensors (e.g., hydrophones H1, H2) may be spaced apart by the separation distance 108 such that, when differenced, the multiple pressure sensors (e.g., hydrophones H1, H2) are configured to provide data useable for reconstructing measurements at locations other than where the multiple pressure sensors are located. In some implementations, the separation distance 108 is at least greater than zero (0) centimeters. In some other implementations, the separation distance 108 is at least greater than fifteen (15) centimeters. Further, in still some other implementations, the separation distance 108 is within a range of fifteen (15) to fifty (50) centimeters. Various other separation distances may be considered and used. In some cases, the separation distance 108 may be greater than a diameter (e.g., 10 cm or less) of the housing 104, if shaped or contoured as a cylinder.

The device 100 may be embodied as multi-component seismic sensor including one or more particle motion sensors along with multiple pressure sensors. For instance, in reference to a multi-component seismic sensor, the device 100 may be configured to detect one or more pressure wavefields (signals) and at least one component of a particle motion that is associated with acoustic signals that may be proximate to the multi-component seismic sensor. In this instance, the device 100 may be configured to calculate seismic survey data in multiple directions including horizontal and vertical directions including, e.g., x-coordinate, y-coordinate, and z-coordinate directions. In some implementations, particle motion sensors may include one or more components of a particle displacement, one or more components (inline (x), crossline (y) and vertical (z) components) of a particle velocity, and/or one or more components of a particle acceleration. Further, the particle motion sensors may include pressure gradient sensors configured to measure change in a pressure wavefield at a particular point with respect to a particular direction. In some cases, one of the pressure gradient sensors may acquire seismic data indicative of, at a particular point, a partial derivative of the pressure wavefield with respect to a crossline direction, and another one of the pressure gradient sensors may acquire, at a particular point, seismic data indicative of pressure data with respect to the inline direction. Thus, in various implementations, as a multi-component seismic sensor, the device 100 may include multiple hydrophones along with one or more geophones, inclinometers, particle displacement sensors, optical sensors, particle velocity sensors, accelerometers, pressure gradient sensors, or combinations thereof.

In accordance with various embodiments, the device 100 can be connected in-line as part of a seabed seismic cable. The device 100 can be configured so as to be spoolable with the cable around a storage drum so that the device 100 is not damaged by the bending moment of the cable. Ability to spool with the cable can aid in the handling and durability of the embodied design in use. According to this embodiment, the sensors can be hydrophones H1 and H2 and can be in-line with the cable, thus having the difference in pressure measurements be along the direction that the cable extends, and thus the housing 104 extends. According to this embodiment, the hydrophones H1 and H2 extend along a direction according to how the cable lies.

According to embodiments, the device 100 can be a separate modular component compared to the cable that connects devices 100. The device can be selfcontained, where in that case the cable does not require and electronics to transmit power or information to or from the device 100. According to that embodiment, the cable can be any flexible member that is connected and has adequate strength to connect two devices 100 in series. The device 100 can also be connected electronically to the cable so as to receive power and to communicate information such as seismic data that is detected.

Figure 2 illustrates a block diagram of the device 100 for acquiring seismic survey data in accordance with implementations of various techniques described herein.

In some implementations, the housing 104 of the device 100 of Figure 1 may be configured as a container to hold a computing system 200 there within. In reference to Figure 2, the computing system 200 may include a computer based system configured to acquire seismic survey data. Further, the computing system 200 may be associated with at least one computing device 204 that may be implemented as a special purpose machine configured to acquire seismic survey data, as described herein. In some cases, the computing device 204 may include any standard element(s) and/or component(s), including one or more processor(s) 210, memory 212 (nontransitory computer-readable storage medium), one or more analog-to-digital converters 214, one or more databases 250, various power sources (e.g., one or more batteries), and various other computing elements and/or components that may not be specifically shown in Figure 2. Further, the computing device 204 may include instructions stored on the non-transitory computer-readable medium 212 that are executable by the at least one processor 210 to acquire seismic survey data, as described herein. Further, in some cases, the computing device 204 may be referred to as a seismic survey device.

In some implementations, the device 100 may include a plurality of sensors, such as, e.g., various types of seismic sensors. For instance, the sensors may include a first pressure sensor 220 (e.g., a first hydrophone), a second pressure sensor 222 (e.g., a second hydrophone), one or more additional pressure sensors 224 (e.g., one or more additional hydrophones), and one or more particle motion sensors 230 (e.g., one or more geophones and/or accelerometers). As described in reference to Figure 1, the multiple pressure sensors 220, 222 may include at least two separate hydrophones, such as a first hydrophone H1 and a second hydrophone H2. Further, the multiple pressure sensors 220, 222 may be spaced apart by a separation distance, such as the separation distance 108 described in Figure 1. Further, the multiple pressure sensors 220, 222 may be configured to acquire seismic survey data, and the computing device 204 may be configured to calculate pressure gradients in multiple directions, including multiple orthogonal horizontal directions.

In some implementations, the computing device 204 may store seismic survey data in the one or more databases 250 for later retrieval. In some other implementations, the computing device 204 may include an onboard communication unit, such as, e.g., a network interface 240, which may be configured to communicate with one or more base stations located onshore or at sea, such as on a rig or vessel. The network interface 240 may be configured for wired communication via a cable, such as, e.g., an ocean bottom cable (OBC), and/or for wireless communication via a wireless transmitter or transceiver, which may be configured for underwater wireless communication. The network interface 240 may be used to transmit data and information associated with multiple sensors, including the first and second pressure sensors 220, 222 (e.g., hydrophones) and/or one or more other sensors 222, 224, 230. The network interface 240 may be configured to send or receive commands particular to a seismic survey.

Figures 3A-3B illustrate a schematic diagram of various deployment techniques of one or more devices configured for acquiring seismic survey data in accordance with implementations of various techniques described herein. In particular, Figure 3A shows a first type of deployment 300A of seismic survey devices 304 via a cable 306, and Figure 3B shows a second type of deployment 300B of the seismic survey devices 304 as stand-alone units or nodes without the use of the cable 306. In various implementations, each of the seismic survey devices 304 may be embodied as instances of the device 100 of Figure 1 and/or Figure 2.

In some implementations, the embodiment of Figure 3A refers to a system or a seismic survey system, that may be configured to use a cable, an undersea cable, or an ocean bottom cable (OBC) 306. The cable 306 may be a dummy cable, or the cable 306 may be used for remote communication of seismic survey data from the seismic survey devices 304 positioned on a seabed or seafloor to one or more remote base stations located onshore or at sea, such as on a rig or vessel. In either instance, the plurality of seismic survey devices 304 (or sensor units) may be coupled (e.g., physically and/or electrically coupled) to the ocean bottom cable 306. In some implementations, each seismic survey device 304 (or sensor unit) may be spaced apart by a first separation distance 307, and each seismic survey device 304 (or sensor unit) may include multiple sensors, including multiple pressure sensors (e.g., multiple hydrophones) spaced apart by a second separation distance 308. As described herein, the pressure sensors (e.g., multiple hydrophones) may be configured to acquire seismic survey data in multiple directions, including multiple orthogonal horizontal directions.

In some implementations, the embodiment of Figure 3B refers to a system or a seismic survey system, that may be configured to use stand-alone seismic survey devices 304 that may be configured for separately storing seismic survey data for later retrieval and/or for separate remote communication of seismic survey data from the seismic survey devices 304 positioned on a seabed or seafloor to one or more remote base stations located onshore or at sea, such as on a rig or vessel. In this instance, the seismic survey devices 304 (or sensor units) may be separately embodied as standalone units or self-contained nodes located on a seabed or seafloor. In some implementations, the seismic survey devices 304 (or sensor units) may be spaced apart by the first separation distance 307, and each seismic survey device 304 (or sensor unit) may include multiple sensors, including multiple pressure sensors (e.g., multiple hydrophones) that are spaced apart by the second separation distance 308. As described herein, the pressure sensors (e.g., multiple hydrophones) may be configured to acquire seismic survey data in multiple directions, including multiple orthogonal horizontal directions.

Further, in some implementations, as described herein, the second separation distance 308 is at least greater than zero (0) centimeters. In other implementations, the second separation distance 308 is at least greater than fifteen (15) centimeters. In some other implementations, the second separation distance 308 is within a range of fifteen (15) to fifty (50) centimeters. In some implementations, various other second separation distances may be considered and used. The multiple pressure sensors (e.g., multiple hydrophones) may be spaced apart by the second separation distance 108 such that, when differenced, the multiple pressure sensors (e.g., hydrophones) are configured to provide data useable for reconstructing measurements at locations other than where the multiple pressure sensors (e.g., hydrophones) are located.

In reference to Figures 3A-3B, the system of seismic survey devices 304 may be used for seismic surveying of underwater features below an ocean bottom surface 22 and into strata 24, 26 beneath the surface 22. In some cases, the term multidimensional may refer to two-dimensional (2D), three-dimensional (3D), more than three-dimensional, or other depending on specific implementations. Further, in some other cases, each of the seismic survey devices 304 may include a seabed sensor housing with multiple seismic sensors, such as multiple hydrophones, and each of the seismic survey devices 304 may refer to a multi-dimensional seismic sensor array or a seismic sensor package having multiple seismic sensors (e.g., multiple hydrophones) as described herein.

As shown in Figures 3A-3B, a marine vessel 10 may be deployed to a survey area specified on a navigation map for seismic surveying. After deployment of the marine vessel 10 to the survey area, a seismic source 18 may be detonated to generate acoustic waves 20 that propagate through the ocean bottom surface 22 and into strata 24, 26 beneath the ocean bottom surface 22. In some implementations, the seismic source 18 may be a conventional air gun, marine vibrator, or non-traditional environmentally friendly source. The seismic source 18 may also include drilling induced acoustic pressure waves, passive seismic noise, or production induced acoustic pressure waves, such as those which may result from water or gas injections, or combinations thereof.

The acoustic signals 20 may be reflected from various subterranean geological formations, such as, e.g., formation 28 depicted in Figures 3A-3B. The incident acoustic signals 20 produce corresponding reflected acoustic signals, or pressure waves 30, which are sensed by the seismic survey devices 304. Further, the seismic survey devices 304 may generate signals referred to as “traces,” which indicate acquired measurements of a pressure wavefield from the multiple pressure sensors and particle motion if the sensors include particle motion sensors. The traces are recorded and may be passed to a data acquisition system 32 disposed on the marine vessel 10. The data acquisition system 32 may include a digitizer, a computer system, and a storage system for storing seismic data acquired during the survey. Further, the storage system may include memory, such as a hard disk drive. In some implementations, seismic data may be recorded continuously over days or months at a time. In other implementations, seismic data may be recorded intermittently, such as after each detonation of the seismic source 18.

The marine vessel 10 may include an onboard network interface 34, which may communicate with each of the seismic survey devices 304 and/or with one or more remote base stations located onshore or at sea, such as on a rig or vessel. The network interface 34 may be used to transmit data and information associated with the marine vessel 10, including position, quality control parameters, time information, and seismic data acquired from each of the seismic survey devices 304. The network interface 34 may transmit or receive commands particular to conducting a seismic survey. The marine vessel 10 may be powered by batteries, which may be recharged by solar panels disposed on the top of the marine vessel 10. In some other cases, the marine vessel may comprise an autonomous robotic type of marine vessel that is capable of self-navigation.

Further, as described in reference to Figures 3A-3B, each of the seabed seismic acquisition devices 304 may include sensor housings spaced along a line, where the sensor housings include at least two independently recorded hydrophones separated in the direction of the sensor housings line. By differencing pressure signals received from the at least two hydrophones, a gradient in a direction of the sensor housings line may be calculated using one or more seismic pressure waves (i.e., P-waves) that may have been recorded by the at least two hydrophones (and an optional vertical geophone). By combining the recorded P-wave and its gradient, the seismic P-wave may be reconstructed on the line between the sensor housings, allowing reduction of a number of sensor housings for adequately sampling a seismic wavefield along this line. The output of each hydrophone may be recorded separately so that the difference may be calculated. Using multiple, separate hydrophones provides for separate measurements.

In some implementations, a seabed seismic survey layout may have several parallel lines of devices 304 (sensor housings). The sensor housings may include at least two hydrophones for measuring seismic P-waves and optionally at least one particle motion sensor for measuring shear waves. The optional particle motion sensors may include horizontal and/or vertical particle motion sensors. Further, spatial sampling the P-waves along a receiver line may impose a maximum distance between sensor housings (Nyquist sampling criteria, depending on the maximum required frequency). This dense sensor sampling may drive a cost of the seabed system. Further, the output of each hydrophone may be separately recorded for calculating differences. In some cases, P-wave spatial sampling may be achieved with sparser sensor housings, e.g., by adding a second hydrophone to the housing, where the multiple hydrophones are mounted at each end of the sensor housing, in the direction of the receiver line. By differencing the two hydrophones, the gradient of the P-wave pressure along the receiver line direction may be determined. The pressure signal differences may be calculated between the two hydrophones, and the differences may be used for interpolation of the recorded signals in between the sensor housings. As such, the measurements from all of The sensor units on the cable or nodes in the line may be combined, and the measurements may interpolated to locations in between The sensor units. This may include interpolation along the cable, and the source may be at any direction. Further, this gradient may be used together with the pressure recording (and optionally vertical particle motion) to determine the P-wave at points between the sensor housings using reconstruction/interpolation algorithms. In some cases, the interpolation process may be used for the purpose of constructing a 3D representation of acquired seismic data, where the 3D representation is substantially unaliased.

In some implementations, the interpolation process may include using a generalized matching pursuit (GMP) technique, as described in commonly assigned U.S. Patent Application Serial No.12/131,870 entitled JOINTLY INTERPOLATING AND DEGHOSTING SEISMIC DATA, now issued U.S. Patent No.7,817,495, which is incorporated herein by reference and described herein. In some other implementations, the interpolation process may include using a multichannel interpolation by matching pursuit (MIMAP) technique on acquired multi-component seismic data, as described in commonly assigned U.S. Patent Application Serial No.12/602,816 entitled METHOD OF REPRESENTING SEISMIC DATA, which is incorporated herein by reference in its entirety.

In this implementation, adequately spatially sampled P-wave data may be generated on a dense grid along the receiver line without a large number of densely spaced sensor housings. In some cases, as described herein, the sensor housings may be coupled together with a cable (e.g., an ocean bottom cable) that provides power to the sensor housing and includes telemetry wires to transmit the seismic data. In other cases, as described herein, the sensor housings may also be autonomous units or nodes that are powered by battery and record the seismic data. These autonomous units or nodes may be coupled or attached to a rope or wire used to deploy and recover them. Further, each of these autonomous units or nodes may be separate and operate independent from one another, and they may be placed in a direction of the receiver line.

In some implementations, the first separation distance 307 is at least greater than zero (0) meters. In some other implementations, the first separation distance 307 is at least greater than twenty-five (25) meters. Further, in still some other implementations, the first separation distance 307 is within a range of twenty-five (25) to fifty (50) meters, or within a range of twenty-five (25) to one-hundred (100) or more meters. As such, the first separation distance 307 may be any number of hundreds of meters. Various other first separation distances may be considered and used.

Figures 4A-4D illustrate various sensor arrangements of a device for acquiring seismic survey data in accordance with implementations of various techniques described herein. In particular, Figure 4A illustrates a top view of a first sensor arrangement 400A taking form of a triangular contour or shape, Figure 4B illustrates a top view of a second sensor arrangement 400B taking form of a diamond contour or shape, and Figure 4C illustrates a top view of a third sensor arrangement 400C taking form of a circular or disk contour or shape. Figure 4D illustrates a side view of any one of the sensor arrangements 400A, 400B, 400C having a side form of a flat contour or shape.

In various implementations, as described herein, the multiple pressure sensors may include two or more hydrophones. Therefore, in some cases, the first arrangement 400A of Figure 4A may include three (3) hydrophones H1, H2, H3 arranged in a triangular contour or shape. In other cases, the second arrangement 400B of Figure 4B may include four (4) hydrophones H1, H2, H3, H4 arranged in a rectangular/diamond contour or shape. In some other cases, the third arrangement 400C of Figure 4C may include four (4) hydrophones H1, H2, H3, H4 arranged in a circular/disk contour or shape. Further, the side view as shown in Figure 4D illustrates that any one of the sensor arrangements 400A, 400B, 400C may have a side form of a flat contour or shape.

Therefore, in various implementations, the sensor housings may be in form of various contours and shapes, such as, e.g., flat base for improved coupling, tubular with or without coupling aid, etc. The sensor housings may be elongated in a direction of line, and the sensor housings may include one or more particle motion sensors (measuring acceleration, velocity, and/ or displacement). The sensor housings may include one or more particle motion sensors for recording all directions of particle motion (e.g., 3C orthogonal sensors). The sensor housings may include at least two 3C sensors that are separated by a distance. Accordingly, the various sensor arrangements 400A, 400B, 400C shown in Figures 4A-4C, respectively, provide various shape options for the sensor housings so as to include multiple hydrophones that are able to acquire seismic signals in the direction perpendicular to the line of seismic sensor housings. In some cases, combinations of geometric shapes may be used. For instance, a triangular shape on a node may be combined on a disk. Further, four (4) hydrophones may be arranged to measure orthogonal differences. Located along the seabed, allow calculation gradient in orthogonal horizontal directions, with or without vertical displacement.

As described herein, multiple hydrophones may be collocated with one or more vertical particle motion sensors. In some cases, the distance between receiver lines may be larger than the spacing between receivers in a line, and in this instance, interpolating the seismic signal across the receiver lines may be calculated. Further, in reference to any of the contours or shapes described in reference to Figures 4A-4C, the angle between hydrophones may be taken into account when calculating the differences.

Figure 5 illustrates a process flow diagram of a method for acquiring seismic survey data in accordance with various implementations described herein. It should be understood that even though method 500 may indicate a particular order of execution of operations, in some instances, various certain portions of the operations may be executed in a different order, and on different systems. In other instances, additional operations or steps may be added to and/or omitted from method 500. In some implementations, the computing device 200 of Figure 2 may be configured to perform method 500. In some other implementations, method 500 may be implemented as a program or as a software instruction process that is configured for acquiring seismic survey data.

At block 510, method 500 may dispose a seismic acquisition device on a seabed or seafloor. At block 520, method 500 may acquire seismic survey data with a plurality of sensors coupled to a housing of the seismic acquisition device. The plurality of sensors may include multiple pressure sensors (e.g., multiple hydrophones) spaced apart by a separation distance. At block 530, method 500 may calculate pressure gradients in multiple directions using the plurality of sensors including the two or more pressure sensors (e.g., multiple hydrophones). In some cases, at block 530, method 500 may process pressure signals (wavefields) acquired from each of the sensor units or nodes.

In some implementations, the multiple pressure sensors may be spaced apart by the separation distance such that, when differenced, the multiple pressure sensors (e.g., multiple hydrophones) are configured to provide data useable for reconstructing measurements at locations other than where the multiple pressure sensors (e.g., multiple hydrophones) are located.

In some implementations, the pressure signal difference between multiple pressure sensors (e.g., at least two hydrophones) may be computed. In some cases, the recordings from all of the hydrophones from all of the sensor units along a cable or node line may be added. Further, the pressure signals between the sensor units may then be estimated by interpolating the pressure signal differences. As described above, such interpolation techniques may include the use of GMP, MIMAP, etc.

Implementations of various technologies described herein may be operational with numerous general purpose or special purpose computing system environments or configurations. Examples of computing systems, environments, and/or configurations that may be suitable for use with the various technologies described herein include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, smart phones, tablets, wearable computers, cloud computing systems, virtual computers, marine electronics devices, and the like.

The various technologies described herein may be implemented in the general context of computer-executable instructions, such as program modules, being executed by a computer. Program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Further, each program module may be implemented in its own way, and all need not be implemented the same way. While program modules may execute on a single computing system, it should be appreciated that, in some implementations, program modules may be implemented on separate computing systems or devices adapted to communicate with one another. A program module may also be some combination of hardware and software where particular tasks performed by the program module may be done either through hardware, software, or some combination of both.

The various technologies described herein may be implemented in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network, e.g., by hardwired links, wireless links, or various combinations thereof. In a distributed computing environment, program modules may be located in both local and remote computer storage media including, for example, memory storage devices and similar.

Further, the discussion provided herein may be considered directed to certain specific implementations. It should be understood that the discussion provided herein is provided for the purpose of enabling a person with ordinary skill in the art to make and use any subject matter defined herein by the subject matter of the claims.

It should be intended that the subject matter of the claims not be limited to the implementations and illustrations provided herein, but include modified forms of those implementations including portions of implementations and combinations of elements of different implementations in accordance with the claims. It should be appreciated that in the development of any such implementation, as in any engineering or design project, numerous implementation-specific decisions should be made to achieve developers’ specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort may be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having benefit of this disclosure.

Reference has been made in detail to various implementations, examples of which are illustrated in the accompanying drawings and figures. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the disclosure provided herein. However, the disclosure provided herein may be practiced without these specific details. In some other instances, wellknown methods, procedures, components, circuits and networks have not been described in detail so as not to unnecessarily obscure details of the embodiments.

It should also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element. The first element and the second element are both elements, respectively, but they are not to be considered the same element.

The terminology used in the description of the disclosure provided herein is for the purpose of describing particular implementations and is not intended to limit the disclosure provided herein. As used in the description of the disclosure provided herein and appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify a presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

As used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context. Similarly, the phrase “if it is determined” or “if [a stated condition or event] is detected” may be construed to mean “upon determining” or “in response to determining” or “upon detecting [the stated condition or event]” or “in response to detecting [the stated condition or event],” depending on the context. The terms “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; “below” and “above”; and other similar terms indicating relative positions above or below a given point or element may be used in connection with some implementations of various technologies described herein.

While the foregoing is directed to implementations of various techniques described herein, other and further implementations may be devised in accordance with the disclosure herein, which may be determined by the claims that follow.

Claims (19)

Claims

1. A sensor unit (100, 304), comprising:

a housing (104) that is configured to be connected to at least a first portion of a cable, wherein the housing extends parallel to a direction that the portion of the cable extends; and

at least two pressure sensors (H1, H2, 220, 222) coupled to the housing (104) where the at least two pressure sensors are spaced apart by a separation distance (108) along the direction in which the first portion of the cable extends, wherein

the at least two pressure sensors (H1, H2, 220, 222) are configured to separately record seismic survey data and where the sensor unit (100, 304) comprises a computing device (200), wherein the computing device (200) is configured to:

calculate a difference between the first seismic survey data and the second seismic survey data; and

reconstructing measurements at locations other than where the at least two pressure sensors (H1, H2, 220, 222) are located based on the difference.

2. The sensor unit of claim 1, wherein the housing (104) is configured to be connected to a second portion of cable.

3. The sensor unit of claim 2, wherein the first portion of cable configured to be connected proximate to one end of the housing (104), and the second portion of cable connects to proximate to a second end of the housing (104).

4. The sensor unit of claim 3, wherein the housing (104) configured to be connected between and in-line with the first portion of cable and the second portion of cable.

5. The sensor unit of claim 1, wherein the housing (104) comprises a geometric shape in form of a triangular shape, a rectangular shape, a diamond shape, a circular shape, or a disk shape.

6. The sensor unit of claim 1, wherein a first pressure sensor of the at least two pressure sensors (H1, H2, 220, 222) is configured to record the first seismic data, and wherein a second pressure sensor of the at least two pressure sensors is configured to separately record the second seismic data.

7. The sensor unit of claim 1, wherein the at least two pressure sensors (H1, H2, 220, 222) comprise two or more hydrophones.

8. The sensor unit of claim 1, further comprising one or more particle motion sensors (230) disposed inside the housing.

9. The sensor unit of claim 8, wherein the particle motion sensors (230) comprise one or more geophones, one or more accelerometers, or a combination of one or more geophones and one or more accelerometers.

10. The sensor unit of claim 1, wherein the separation distance (108) is at least greater than fifteen centimeters.

11. The sensor unit of claim 1, wherein the separation distance (108) is within a range of fifteen to fifty centimeters.

12. The sensor unit of claim 1, wherein the computer device is configured to calculate one or more pressure gradients in multiple orthogonal horizontal directions based on the first seismic survey data and the second seismic survey data.

13. A system for seismic surveying of underwater features below an ocean bottom surface (22) and into strata (24) , comprising:

an ocean bottom cable (306); and

a plurality of sensor units (304) disposed along the ocean bottom cable (306), wherein each sensor unit (304) is spaced apart by a first separation distance (307), and wherein each sensor unit (304) comprises at least two pressure sensors (H1, H2, 220, 222) spaced apart by a second separation distance (108), and wherein a computing device is configured to:

calculate a difference in pressure signals between the at least two pressure sensors (H1, H2, 220, 222) in a sensor unit (304); and

reconstruct pressure signals at locations between the plurality of sensor units (304) other than where the at least two pressure sensors (H1, H2, 220, 222) are located based on the difference, wherein the at least two pressure sensors (H1, H2, 220, 222) are configured to separately record seismic survey data for calculating differences between sensed pressure gradients.

14. The system of claim 14, wherein the first separation distance (307) is within a range of twenty-five (25) to one hundred (100) meters.

15. The system of claim 14, wherein the second separation distance (108) is within a range of fifteen (15) to fifty (50) centimeters.

16. A method for processing seismic data, comprising:

receiving seismic data that has been acquired using sensor units (304) disposed along an ocean bottom cable (306), wherein each sensor unit (304) comprises at least two pressure sensors (H1, H2, 220, 222) that are spaced apart by a first separation distance (108); and

calculating a difference in pressure signals between the at least two pressure sensors (H1, H2, 220, 222) to obtain pressure signals at locations between the sensor units (304) wherein the at least two pressure sensors (H1, H2, 220, 222) are configured to separately record seismic survey data for calculating differences between sensed pressure gradients; and

reconstructing pressure signals at locations between the at least two pressure sensors (H1, H2, 220, 222) other than where the at least two pressure sensors (H1, H2, 220, 222) are located based on the difference.

17. The method of claim 16, wherein calculating the difference in pressure signals generates pressure gradients in a direction along the ocean bottom cable.

18. The method of claim 16, wherein the first separation distance (108) is within a range of fifteen to fifty centimeters.

19. The method of claim 16, wherein the sensor units (304) are spaced apart by a second separation distance (307) within a range of twenty-five to one hundred meters.