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Detection and localization of seafloor hydrocarbon and related fluid seeps using Ocean Acoustic Waveguide Remote Sensing ( OAWRS)

IP.com Disclosure Number: IPCOM000218078D
Publication Date: 2012-May-18
Document File: 3 page(s) / 34K

Publishing Venue

The IP.com Prior Art Database

Abstract

In the oil and gas industry, modeling of the subsurface is typically utilized for visualization and to assist with analyzing the subsurface volume for potential locations for hydrocarbon resources. Accordingly, various methods exist for estimating the geophysical properties of the subsurface volume (e.g., information in the model domain) by analyzing the recorded measurements from receivers (e.g., information in the data domain) provided that these measured data travel from a source, then penetrate the subsurface volume represented by a subsurface model in model domain, and eventually arrive at the receivers. The measured data carries some information of the geophysical properties that may be utilized to generate the subsurface model. However, in certain measurements in marine or artic environments, other objects may introduce interference with the measured data. For example, a survey may include a source that generates a signal, which is transmitted through the subsurface, and receivers that are positioned to detect the reflected signals. As the signal travels through the body of water, it may have various sources of interference that disrupt the signal. For example, schools of fish, whales, submarines, nets or other objects within the body of water may interfere with the measurements and introduce noise into the survey data. These surveys may include seismic surveys, electromagnetic surveys or others data types. To address such interference, ocean acoustic waveguide remote sensing (OAWRS) technology has been developed and used to rapidly detect schools of fish and other objects in the body of water at distances of hundreds to thousands of kilometers. An acoustic waveguide can be formed in a layer with sufficient impedance differences from its surrounding media due to the coupling of waves reflected at the boundaries. In the ocean environment, the water surface, water bottom, and any kind of sound speed change due to temperature, pressure, or salinity difference naturally provide waveguides. Waveguides can propagate acoustic energy within the layer for long distances with small attenuation. In comparison, seismic p-wave amplitudes decrease rapidly because of spherical divergence (and attenuation). Thus, ocean waveguides can be used to scan a large water volume. OAWRS was developed by academia and has been successfully utilized to monitor fish schools (Makris et al. 2006) and oceanic ridges (Makris et al. 1995) in oceanographic research. Beneficially, this (OAWRS) technology may be utilized in a variety of other processes. For instance, this method can be adapted to detect and map hydrocarbon seafloor seeps over wide areas, from shallow to deep ocean environments. Similar to fish schools, the seep-caused impedance changes relative to the surrounding water body could possibly be captured on the waveguide image. For example, see the following website that proposes the detection of CO2 bubbles by using. See, e.g., OAWRS.http://www.ieaghg.org/co2tool_v2.2.2_product_joomla/ technique_descriptions/bubble_stream_detection.html. Further, the method may include calibrating the survey parameters of OAWRS for it to be better suited for detection of the hydrocarbon seeps. For example, one may tune high-frequency sound waves to the resonance frequency of the 0.1 – 1.0 centimeter (cm) bubbles typically observed in seafloor seeps plumes, to increase the target strength. One may also change the directivity pattern of the sound transmitters depending on the characteristics of the specific waveguides in the survey area. Because OAWRS can provide continuous monitoring over large areas, it should be possible to find and locate intermittent seeps from the seafloor. Other conventional technologies used to detect ocean bottom seeps, such as multibeam sonar, may fail in this situation because the seep may be intermittent (e.g., the seep is inactive when such data are acquired). Backscattering from water disturbances unrelated to seeps could also be monitored to discriminate against such features. The steps required to detect hydrocarbon and related fluid seeps using OAWRS are summarized below. 1. Survey a target area using the OAWRS method. To optimally detect hydrocarbon seeps, several components such as transmitter and receiver equipment, acquisition geometry, waveforms (e.g., frequency) transmitted for sensing, etc., may need to be modified or adjusted, as is known to those skilled in the art. 2. Process the acquired data using the OAWRS method to obtain an image of the water column (typically impedance changes) over the acquisition area. 3. Recognize the bubble plumes (vertical direction dominated scattering energy) on the water column image. 4. Track this anomaly down to sea floor to identify the seep location. Note that even when the water column conditions are not conducive to form a waveguide, the OAWRS technology could be employed to detect impedance changes caused by hydrocarbon seeps. However, due to larger spreading losses, the scanning range of the technology would be much smaller. Based on the identified seeps, the various actions may be performed. As an example, the composition of the seeps may be identified to enhance models of the subsurface associated with the seeps. This identification may be utilized to enhance hydrocarbon recovery or production. The seep may be utilized as an input into a subsurface model, which may be utilized to provide the location of subsurface resources. With this information, a wellbore may be drilled to provide a flow path from a region of the subsurface volume to a hydrocarbon processing facility to further process the hydrocarbons recovered from the subsurface volume. Also, with the seep location, different means of recovering the hydrocarbons may be utilized. Key References: Makris, N. C., Avelinio, L. Z. and Menis, R., 1995. Deterministic reverberation from ocean ridges. J. Acous Soc. Am., 95, 3547-3574. Makris, N. C., Ratilal, P., Symonds, D. T., Jagannathan, S., Lee, S. and Nero, R. W., 2006. Fish population and behavior revealed by instantaneous continental shelf–scale imaging. Science 311, 660-664. Makris, N. C., Ratilal P., Jagannanathan, S., Gong, Z., Andrews, M., Bertsatos, I., Godø, O. R., Nero, R. W., and Jech., J. M., 2009. Critical population density triggers rapid formation of vast cceanic fish shoals. Science 323, 1734-1737.

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Detection and localization of seafloor hydrocarbon and related fluid seeps using Ocean Acoustic Waveguide Remote Sensing (OAWRS)

In the oil and gas industry, modeling of the subsurface is typically utilized for visualization and to assist with analyzing the subsurface volume for potential locations for hydrocarbon resources.  Accordingly, various methods exist for estimating the geophysical properties of the subsurface volume (e.g., information in the model domain) by analyzing the recorded measurements from receivers (e.g., information in the data domain) provided that these measured data travel from a source, then penetrate the subsurface volume represented by a subsurface model in model domain, and eventually arrive at the receivers.  The measured data carries some information of the geophysical properties that may be utilized to generate the subsurface model.

However, in certain measurements in marine or artic environments, other objects may introduce interference with the measured data.  For example, a survey may include a source that generates a signal, which is transmitted through the subsurface, and receivers that are positioned to detect the reflected signals.  As the signal travels through the body of water, it may have various sources of interference that disrupt the signal.  For example, schools of fish, whales, submarines, nets or other objects within the body of water may interfere with the measurements and introduce noise into the survey data.  These surveys may include seismic surveys, electromagnetic surveys or others data types. 

To address such interference, ocean acoustic waveguide remote sensing (OAWRS) technology has been developed and used to rapidly detect schools of fish and other objects in the body of water at distances of hundreds to thousands of kilometers.  An acoustic waveguide can be formed in a layer with sufficient impedance differences from its surrounding media due to the coupling of waves reflected at the boundaries.  In the ocean environment, the water surface, water bottom, and any kind of sound speed change due to temperature, pressure, or salinity difference naturally provide waveguides. Waveguides can propagate acoustic energy within the layer for long distances with small attenuation. In comparison, seismic p-wave amplitudes decrease rapidly because of spherical divergence (and attenuation). Thus, ocean waveguides can be used to scan a large water volume. OAWRS was developed by academia and has been successfully utilized to monitor fish schools (Makris et al. 2006) and oceanic ridges (Makris et al. 1995) in oceanographic research.

Beneficially, this (OAWRS) technology may be utilized in a variety of other processes.  For instance, this method can be adapted to detect and map hydrocarbon seafloor seeps over wide areas, from shallow to deep ocean environments.  Similar to fish schools, the seep-caused impedance changes relative to the surrounding water body could possibly be captured on the...