Patent Publication Number: US-2017371071-A1

Title: Towed remote controlled vehicle for seismic spread intervention and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority and benefit from U.S. Provisional Patent Application No. 62/353,644, filed on Jun. 23, 2016, entitled “Towed ROV for interventions in the spread,” the entire disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for using a towed remotely operated vehicle (ROV) under water for performing various operations on a streamer spread. 
     Discussion of the Background 
     Marine seismic data acquisition and processing generate a profile (image) of the geophysical structure (subsurface) under the seafloor. While this profile does not provide an accurate location for the oil and gas, it suggests, to those trained in the field, the presence or absence of oil and/or gas. Thus, providing a high-resolution image of the subsurface is an ongoing process for the exploration of natural resources, including, among others, oil and/or gas. 
       FIG. 1  illustrates a marine seismic data acquisition system  100 . In this vertical view, a vessel  110  tows seismic sources  112   a  and  112   b  and a streamer spread  114  having plural streamers (only one streamer  115  is shown in the figure) at predetermined depths under the water surface  111 . Although only one streamer  115  is visible in this vertical view, plural streamers are typically spread in a three-dimensional volume. Streamer  115 , which has a tail buoy  118  and likely other positioning devices attached, houses seismic receivers/sensors  116 . 
     The seismic sources generate seismic waves such as  120   a  and  120   b  that propagate through the water layer  30  toward the seafloor  32 . At interfaces (e.g.,  32  and  36 ) between layers (e.g., water layer  30 , first layer  34 , and second layer  38 ) inside which the seismic waves propagate with different wave propagation velocities, the waves&#39; propagation directions change as the waves are reflected and/or transmitted/refracted/diffracted. Seismic waves  120   a  and  120   b  are partially reflected as  122   a  and  122   b  and partially transmitted as  124   a  and  124   b  at seafloor  32 . Transmitted waves  124   a  and  124   b  travel through first layer  34 , are then reflected as waves  126   a  and  126   b , and transmitted as  128   a  and  128   b  at interface  36 . At the surface of reservoir  40 , waves  128   a  and  128   b  are then partially transmitted as waves  130   a  and  130   b  and partially reflected as waves  132   a  and  132   b . The waves traveling upward may be detected by receivers  116 . Maxima and minima in the amplitude versus time data recorded by receivers carry information about the interfaces and traveling time through layers. 
     A bird view of this configuration is illustrated in  FIG. 2 , which shows the seismic acquisition system  100  including the vessel  110 , which tows two super wide tow ropes  142  provided at respective ends with deflectors  144 . Plural lead-in cables  146  are connected to streamers  115  (for simplicity, only a few streamers are illustrated). The plural lead-in cables  146  also connect to the towing vessel  110 . Streamers  115  are maintained at desired separations from each other by separation ropes  148 . Plural sources  112  are also connected to the vessel  110  through corresponding umbilicals  113 . The streamers, deflectors, various ropes and lead-ins, wide tow ropes and birds for a streamer spread  140 . 
       FIG. 2  offers a better understanding of the complexity of the streamer spread than  FIG. 1 . The operator of the seismic survey is faced not only with the complexity of the streamer spread (e.g., maintaining all these elements untangled), but also with the fact that the streamer spread needs constant maintenance due to the various issues that it encounters during a seismic survey (e.g., barnacle deposits, obstacle management, spread monitoring, spread inspection). 
     Traditionally, these issues associated with the streamer spread require workboat operations, i.e., an additional boat is launched from the towing vessel  110  and this workboat approaches the streamer that needs attention, and one or more persons on this workboat manually perform the work necessary to address the specific issue. Alternatively, if the issue cannot be solved from a workboat or workboat operations are not allowed, due to local regulations, the seismic survey is halted and the streamer spread is recovered on the towing vessel for performing the necessary work. Both operations may lead to certain down time for the seismic survey, which is undesirable and costly. 
     Moreover, workboat operations are complex and tricky. In addition, these operations are weather dependent (i.e., bad weather prevents the launch of a workboat) and they must occur during the day so that the working personnel can see the streamer spread whereas the seismic survey is performed day and night without pause. 
     Because of these dependencies, the workboat or recovery operations are not as efficient as needed by the operator of the seismic survey. 
     Thus, there is a need for another approach to these issues, that is capable to perform various operations as soon as needed, irrespective of the time of day or night and irrespective of the weather conditions. 
     SUMMARY 
     According to an embodiment, there is a seismic data acquisition system that includes a streamer spread including (i) a streamer having receivers for recording seismic data and (ii) a connecting cable connecting the streamer to a towing vessel; a collar device configured to move along the connecting cable, between the towing vessel and the streamer; and a remotely operated vehicle, ROV, attached to the collar device with an umbilical and configured to carry an interchangeable payload. 
     According to another embodiment, there is a payload system for performing various operations on a streamer spread of a marine seismic data acquisition system. The payload system includes a collar device to be attached to a connecting cable, which extends between a towing vessel and a streamer of the marine seismic data acquisition system; and a remotely operated vehicle, ROV, attached to the collar device with an umbilical and configured to carry an interchangeable payload. 
     According to still another embodiment, there is a method for performing various operations on a streamer spread of a marine seismic data acquisition system. The method includes attaching a collar device to a connecting cable, which extends between a towing vessel and a streamer; connecting a remotely operated vehicle, ROV, to the collar device with an umbilical; attaching a desired interchangeable payload to the ROV; and operating the collar device along the connecting cable and controlling a length of the umbilical to position the ROV at a desired position of the streamer spread for performing one operation of the various operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings: 
         FIG. 1  is a side view of a conventional marine seismic acquisition system; 
         FIG. 2  is a top view of the conventional marine seismic acquisition system; 
         FIG. 3  illustrates a marine seismic acquisition system having an ROV for performing various functions on the streamer spread; 
         FIG. 4  illustrates a connection between the ROV and a vessel that tows the streamer spread; 
         FIG. 5  illustrates a marine seismic acquisition system having an ROV controlled by a collar device for performing various functions on the streamer spread; 
         FIG. 6  illustrates a marine seismic acquisition system having an ROV controlled by two collar devices for performing various functions on the streamer spread; 
         FIG. 7  illustrates a first configuration of the collar device that controls the ROV; 
         FIG. 8  illustrates a second configuration of the collar device that controls the ROV; 
         FIG. 9  illustrates a third configuration of the collar device that controls the ROV; 
         FIG. 10  illustrates a fourth configuration of the collar device that controls the ROV; 
         FIG. 11  illustrates a fifth configuration of the collar device that controls the ROV; 
         FIGS. 12A and 12B  illustrate an ROV being controlled with two collar devices; 
         FIGS. 13A and 13B  illustrate how a depth of the ROV may be controlled with the collar device; 
         FIGS. 14A and 14B  illustrate the use of a float attached to the collar device or the Roy; 
         FIG. 15  illustrates a configuration of the Roy; 
         FIG. 16  illustrates the use of plurality ROVs with a streamer spread; and 
         FIG. 17  is a flowchart of a method for performing various operations with an ROV on a streamer spread. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of a streamer spread. However, the embodiments to be discussed next are not limited to this structure, but they may be applied to other structures that are towed under water. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner with other features or structures in one or more embodiments. 
     According to an embodiment illustrated in  FIG. 3 , a seismic data acquisition system  300  includes, in addition to a towing vessel  310  and a streamer spread  340 , at least one ROV  350  that is towed by the towing vessel  310 . ROV  350 , as discussed later, may have various systems for controlling its position relative to spread. For example, the ROV  350  may have wings and/or a buoyancy system for adjusting its position along a vertical direction Z, and/or it may have wings for adjusting its position along a cross-line direction Y, which is perpendicular to the inline direction X and the vertical direction Z. 
       FIG. 3  shows the ROV  350  being towed by vessel  310  with a towing mechanism  360 . This towing mechanism allows to adjust the position mainly in X direction. Towing mechanism  360  may be as simple as a cable as illustrated in  FIG. 3  and a winch located on the towing vessel. However, the towing mechanism  360  may be more sophisticated as discussed later. A position of the ROV  350  may be adjusted along the inline direction X, cross-line direction Y and/or the depth direction Z with the towing mechanism  360 . 
       FIG. 4  illustrates a side view of the ROV  350 , being deployed in water and located under the streamer  315 . This figure also shows a head of the streamer being held at a given depth by a head float  315 A. Note that head float  315 A may float at the water surface  311 , or under this surface. A winch  362  is shown installed at the back of the towing vessel  310  and connecting to one end of the towing mechanism  360 . 
     ROV  350  is shown having vertical wings  352 , for controlling its location along the cross-line direction Y, and also having a payload  354 . Payload  354  can be a plug and play payload, i.e., an interchangeable load that is attached to the ROV  350  as needed. In other words, an interchangeable load is a load from a plurality of loads that may be attached to a given port of the ROV and any of these plural loads that can be interchanged with one another and be attached to the given port, depending on the operation to be performed by the ROV. Payload  354  may fulfill various objectives, for example, it may be a cleaning device for cleaning the streamers and other cables, a deployment payload that hosts a cleaning device, an inspection payload that performs video data gathering and/or connects to various elements of the streamer spread for collecting recorded data, an operating payload that may include a controllable arm for removing debris that sticks to the various elements of the streamer spread, an operating payload that activates or communicates with an equipment on the spread. This means that the ROV  350  is compatible with various payloads. 
     The embodiments of  FIGS. 3 and 4  indicate that ROV  350  has the following characteristics: can be towed by a vessel (towing vessel  310  or another vessel), can be steerable, can be controlled from the mother vessel, can be supplied with power from the mother vessel, can sent information about the streamer spread to the mother vessel in real time, and can connect to various payloads as needed. One skilled in the art would note that this ROV can operate day or night, in good or bad weather and thus, the health and safety of the personnel operating the device is not at risk. 
     More details about the ROV and its connection to the mother vessel are now discussed with regard to the figures.  FIG. 5  shows an embodiment in which a seismic data acquisition system  500  includes a towing vessel  510  and a streamer spread  540 . The streamer spread includes plural streamers  515  connected to the vessel through corresponding lead-ins  546 . Two wide tow ropes  542  are shown sandwiching the plural lead-ins  546 . 
     In this embodiment, the ROV  550  is connected to the vessel  510  through a towing mechanism  560 , which includes a collar device  564  attached either to the lead-in  546  or the wide tow rope  542 . The towing mechanism  560  also includes a first cable  563  that connects the collar device  564  to the towing vessel, and a second cable  566  that connects the collar device to the ROV  550 . In one application, the first and second cables may be the same cable, as discussed later. 
     Collar device  564  may move up and down along the lead-in or wide tow rope when controlled by a global controller  510 A located on the vessel. By adjusting the position of the collar device  564  along the lead-in or wide tow rope, a cross-line position of the ROV  550  along the Y axis can be adjusted. By adjusting a length of the second cable  566  with the controller  510 A, an inline position of the ROV  550  along the X axis can be adjusted. Thus, the position of the ROV  550  in the XY plane is adjustable. By adjusting the various wings located on the ROV, as the ROV is towed by the vessel  510  with a given speed, its depth position along the Z axis can be adjusted. This means that the ROV&#39;s position is fully controllable by controller  510 A and thus, the ROV can be moved along the streamer or any other component of the streamer spread for performing the desired function. 
     Another configuration of the ROV is illustrated in  FIG. 6  in which seismic data acquisition system  600  includes a towing vessel  610  and a streamer spread  640 . In this case, the ROV  660  is connected to two sliding collar devices  664 A and  664 B, each capable of sliding on a corresponding lead-in  646  or wide tow rope  642 . Two cables  666 A and  666 B connect the ROV  660  to the two collar devices  664 A and  664 B, respectively. According to this embodiment, the length of cables  666 A and  666 B is controlled independently from the controller  610 A so that both the inline and cross-line position of the ROV can be controlled with these two cables. 
       FIG. 7  illustrates a seismic data acquisition system  700  in which a collar device  764  is located on a lead-in  746  (or wide tow rope  742 , generically called herein connecting cable), which is connected between the towing vessel  710  and a corresponding streamer  715 . Streamer  715  includes seismic receivers  716  (only one is illustrated for simplicity). A single cable  763  (ROV umbilical) extends from the vessel  710  to the ROV  750  through collar device  764 . ROV  750  is shown in the figure having a payload  754 . The collar device, ROV umbilical and the ROV may be called herein a payload system because this system carries a payload for performing various operations on the streamer spread. ROV umbilical  763  may be a conduit for exchanging electric power, pressurized air, data, and/or commands between the vessel or the collar device and the ROV. As shown in the enlarged detail of the collar device  764 , ROV umbilical  763  passes a pulley  768  attached to a frame  770  of the collar device  764 . Frame  770  also has an orifice  772  through which the lead-in  746  extends. A swivel  774  is attached to the frame  770  and can swivel relative to the frame. A collar control cable  776  connects the swivel  774  to a winch  762  (similar to winch  362  in  FIG. 3 ) located on vessel  710 . Collar control cable  776  is used to adjust the position of the collar device  764  along the corresponding lead-in  746  or wide tow rope  742 . A winch  762 ′, located on the vessel, may also be used to control a length of the ROV umbilical  763 , and thus, the inline position of the ROV. 
     With this arrangement, the position of the ROV may be controlled relative to the streamer spread  740  anywhere between the source  712  and deflector  744 . One skilled in the art would understand that a similar arrangement may be used on the other side of the source  712  for controlling the other half of the streamer spread. 
     Instead of having the control winch  762  on board the vessel  710  as in the embodiment of  FIG. 7 , it is possible to place it on the collar device as illustrated in  FIG. 8 . In this case, the collar control cable  776  is configured to transmit power, data and/or commands so that the controller  710 A can remotely control the winch  762 . 
     To reduce the number of cables used to control the ROV  750  and collar device  764 , the embodiment illustrated in  FIG. 9  has the ROV umbilical  763  extending only from the collar device  764  to the ROV  750  and not from the vessel  710 . For this configuration, the winch  762 ′ is present on the collar device  764  and not on the vessel  710 . Thus, for this embodiment, both winches  762  (for controlling the position of the collar device along the lead-in or wide tow rope) and  762 ′ (for controlling the position of the ROV along the inline direction) are located on the collar device. For this situation, the power, data and/or commands are exchanged between the vessel and the collar device via the collar control cable  776 . 
     A further embodiment illustrated in  FIG. 10  shows the collar device  764  being completely autonomous, i.e., not being tethered to the vessel with either collar control cable  776  or ROV umbilical  763 . In this case, the collar device  764  has an actuation device  780  attached to frame  770  and the actuation device  780  is capable to move along lead-in  746  or wide tow rope  742 . The actuation device  780  may include caterpillars or gripping wheels  782  actuated by a motor  784  for moving along the lead-in. In one embodiment, motor  784  is a linear magnetic motor that uses the lead-in as a magnetic core. For such configuration, commands and/or data can be exchanged with the controller  710 A via a transceiver  786  mounted on the collar device. Transceiver  786  may be an acoustic modem or another electronic device that is capable to transmit and receive signals along a cable, for example, the lead-in  746 . Collar device  764  may also include a local processor  788  for coordinating the actuation mechanism, the transceiver and the various winches located on the frame  770 . 
     The collar device  764  illustrated in  FIG. 10  also requires a power source. This power source  790  may be implemented as a battery, fuel cell, hydrogenator, and be either located on the collar device as illustrated in  FIG. 10 , or on the ROV itself. In this regard,  FIG. 11  shows an embodiment in which the collar device  764  has a hydrodynamic mechanism  783 , e.g., a wing, for moving the collar device along the lead-in or wide tow rope. An orientation of the wing may be controlled by the local controller  788  to achieve the desired movement of the collar device. 
     The embodiments illustrated in  FIGS. 7-11  suggest that the ROV&#39;s position can be controlled in the XY plane only on one half of the streamer spreader.  FIGS. 12A and 12B  show that by using two collar devices  764 A and  764 B, implemented as any of the configurations discussed above with regard to  FIGS. 7-11 , and corresponding ROV umbilicals  763 A and  763 B, it is possible to control the position of the ROV over the entire streamer spread in the XY plane.  FIG. 12A  shows the collar devices  764 A and  764 B located on corresponding lead-ins  746  while  FIG. 12B  shows the collar devices being located on corresponding wide tow ropes  742 . 
     Regarding the vertical positioning of the ROV,  FIG. 13A  shows the ROV  750  having vertical fins  752  for controlling a position in the XY plane and horizontal fins  754  for controlling a vertical position along the Z axis.  FIG. 13A  is a side view of the seismic data acquisition system, with the streamer  715  being connected to a head buoy  715 A that floats at the water surface  711 . Collar device  764  is shown being attached to the vessel  710  with collar control cable  776  and ROV  750  is attached to ROV umbilical  763 . Although this embodiment shows the collar control cable and the ROV umbilical as in the embodiment of  FIG. 7 , any of the configurations discussed in  FIGS. 8-11  may be implemented in the embodiment of  FIG. 13A .  FIG. 13B  shows that by moving the collar device  764  closer to vessel  710 , the vertical position H of the ROV can be adjusted, even if no fins are used. Those skilled in the art would understand that the vertical position of the ROV may also be adjusted with a buoyancy mechanism similar to that of a submarine. 
     According to another embodiment illustrated in  FIG. 14A , a collar device float  790  may be connected to a winch  792  attached to the collar device  764 . In this case, either the local controller  788  of the collar device, or the global controller  710 A of the vessel, may actuate the winch  792  for adjusting a length of the link  796  connecting the winch  792  to the collar device float  790 . Optionally, the link may be attached to the ROV umbilical  763 . 
       FIG. 14B  shows a similar embodiment in which both a winch  792 ′ and a float  790 ′ are located at the ROV and not at the collar device as in the embodiment of  FIG. 14A . The winch  792 ′ is attached to the ROV while the float  790 ′ floats at the water surface  711 . In one embodiment, the float is configured to float under the water surface. 
     The embodiments discussed above disclose various ways for positioning the ROV in a horizontal plane (XY), substantially parallel to the water surface, but also in a vertical direction. However, to know where the ROV is and to adjust its position accordingly, the ROV may include one or more sensors for determining its position. For example, as illustrated in  FIG. 15 , the ROV  1500  may have a depth sensor  1502  for determining its vertical position. The depth sensor  1502  may be connected, via a bus  1504 , to a processor  1506 . Processor  1506  is configured to receive data from the depth sensor and other sensors or mechanisms of the ROV, and process them. The processor  1506  is connected to a memory  1508  for storing associated information. 
     As previously discussed, the ROV may include a buoyancy system  1510  for regulating its depth. Buoyance system  1510  may be controller by processor  1506 . Processor  1506  may communicate with the global controller  710 A located on the vessel  710  either in a wired manner, through the ROV umbilical  1512 , or in a wireless manner, through a modem or transceiver  1514 . A power source  1516  may supply with power all these components or the power may be supplied from the ROV umbilical  1512 . 
       FIG. 15  also shows one or more motors  1520  capable of actuating vertical wings  1522  and/or horizontal wings  1524 . Motor  1520  is controlled by processor  1506 . A port  1530  shown on the top of ROV  1500  (it may be located on the bottom of the ROV, on its side, on its nose or tail) is configured to connect to a desired interchangeable payload. 
     The position of the ROV when under water may be detected with various systems. In one application, a seismic spread acoustic network triangulation system (i.e., various sensors located on the streamers generate acoustic waves and other sensors record the acoustic waves for determining the positions of the streamers) that is used for determining the positions of the streamers may be extended to cover the ROV and determine its position. Alternatively, an ultra-short base line (USBL) system installed on the vessel or one or more of the floats (e.g., streamer floats) may determine the position of the ROV. Still another possibility is to make the ROV to emit a noise in the seismic bandwidth of the receivers of the streamers and to use the data collected by the streamers to determine the position of the ROV. Still another possibility is to use magnetic coding along the cables and streamers for determining the position of the ROV. Those skilled in the art, based on this disclosure, would be able to come with other ways to monitor the position of the ROV under water. 
     To improve the efficiency of the ROV when under water, in one application, is possible to deploy plural ROVs. The ROVs may be deployed in parallel or in series. For example, while  FIG. 7  shows a single ROV on the right hand side of the streamer spread, it is possible to have an additional ROV on the left hand side of the streamer spread, with the same configuration as the ROV on the right hand side. Alternatively, the ROVs may be deployed in series as illustrated in  FIG. 16 . Having plural ROVs increases the efficiency of their operations.  FIG. 16  also shows each ROV having a cleaning mechanism as payload, e.g., ROV  750  has cleaning mechanism  754  and ROV  1650  has cleaning mechanism  1654 . Although this figure shows the ROVs moving in between the streamers, in one application, the ROV(s) may attach with their payloads to the streamers and move along them for example, for cleaning operations. 
     The payload may be used to execute various operations. For example, the payload may be used to (1) clean the seismic spread from barnacles, e.g., using a scraper type tool, from fishing and debris caught in the spread, e.g., using mechanical means as cutter, pliers, (2) do preventive/curative maintenance on the spread as for example, changing batteries or parts (bird, compass, acoustics, etc.), refilling anti-barnacle devices (chemical or one that uses a scrapper), calibrate sensors, e.g., hydrophone, acoustic, depth sensors, perform visual inspection of the streamer spread, and/or detect air leaks on sources, and/or (3) execute specific tasks as deploying a PAM system on the spread, performing CTD (conductivity, temperature vs Depth) measurements, measuring currents everywhere on the spread, deploying mechanical sensors along the spread, assisting in cable separation operations in case of a crash (if motorized ROV), assist in streamer operation handling (for example, connect the ROV to the middle of the streamer, transfer a tension on the ROV umbilical, recover a first part of the streamer with the ROV supporting tension, release the ROV and recover a second part of the streamer), or assist or even perform section change (streamer reconfiguration). Those skilled in the art, based on this disclosure, would find other ways of using the ROV described herein. 
     Based on the above discussed embodiments, a method for performing various operations on a streamer spread of a marine seismic data acquisition system is now discussed with regard to  FIG. 17 . The method includes a step  1700  of attaching a collar device  764  to a connecting cable  746 ,  742 , which extends between a towing vessel and a streamer, a step  1702  of connecting an ROV  750  to the collar device  764  with an umbilical  763 , a step  1704  of attaching a desired changeable payload  754  to the ROV, and a step  1706  of operating the collar device along the connecting cable and controlling a length of the umbilical to position the ROV at a desired position of the streamer spread for performing one operation of the various operations. 
     Those skilled in the art would understand that although the above embodiments disclose a collar, any device that functions as the collar may be used. For example, the collar may be replaced with a pulley or sheave attached to the lead-in and the position of the ROV is controlled by adjusting the length of the ROV umbilical. 
     The above-discussed embodiments provide a system and a method for positioning an ROV about a streamer spread and performing at least one operation with the ROV on at least one component of the streamer spread. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details. 
     Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. 
     This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.