METHOD AND APPARATUS DETECTING AND ANALYZING OIL AND GAS COMPOSITIONS USING DUAL SENSORS
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] Detection of Oil and Gas in the ocean is relevant from both an exploration and production viewpoint. On the exploration side, oil and gas is located in some instances under the seafloor, or in the case of methane ice or condensed hydrocarbons, at the seafloor. Extracting and selling that oil and gas can constitute a lucrative business. However, locating sub-seafloor oil and gas is difficult and expensive, with a typically marginal chance of success.
[0002] Oil and gas located below the seafloor can in some instances move toward the seafloor and exit into the water column through vents, seeps or other faults in the seafloor, or by moving through seafloor sediments. It is apparent to one skilled in the art that identifying locations where such "plumes" of oil and gas occur in the water column can allow indication of seafloor locations where subsurface oil and gas is present.
[0003] Furthermore, monitoring such plumes once identified will allow oceanographers and industry to further understand the flux or concentration gradients around these areas. Such knowledge and information will assist in identify other sources of plumes and forecast reservoir potential.
[0004] On the production side, oil and gas is typically transported from production platforms or ships to onshore holding and refining facilities. Transportation lines can extend several miles offshore to the production platforms or ships. The prompt identification of leaks in the transfer lines and around the drilling platforms is necessary to prevent system and delivery failures. Furthermore there is a need for a preventive maintenance tool-
where minor (or micro) leaks are identified and rectified as part of a wider maintenance and repair program, or where a leakage check is included in the equipment installation protocols.
[0005] Efforts to use hydrocarbon "sniffers" and chemical analyzers to locate oil and gas plumes and leaks in seawater have had limited success to date. Most sensors, such as the METS sensor, have inappropriate dynamic ranges or too slow response times to be of use by themselves. Some other sensors, such as Raman spectroscopy, have suitable response time but only limited sensitivity.
[0006] The first part of this invention relates to a method of using two sensors.
[0007] One sensor which is very sensitive to oil and gas in the water column but having some drawback, such as being less sensitive to chemical composition, being slower in response time, etc. is used, and a second sensor which is less sensitive to oil and gas in the water column but having other advantages such as being more sensitive to chemical composition of the water samples, being faster in response, etc.
[0008] These two sensors are then used in concert to locate and characterize oil and gas plumes in oceanic or other water columns or leaks in oil production and transfer facilities.
[0009] For example, in the Gulf of Mexico the background concentration of methane is only a few micromolar. This may be less than that detectable by a fast response sensor such as Raman spectroscopy. However, it may be detectable using a highly sensitive technique such as fluorescence spectroscopy. Furthermore, micro leaks in oil and gas pipelines may be difficult to detect with Raman spectroscopy due to a limited detection limit, but the leaks may be localized with a more sensitive, and non-reversible
sensor such as METS. Thus, the Raman spectroscopy may be used to pinpoint the location of micro-leaks once the leak area is localized.
[0010] Conversely, the concentration of methane in oil and gas plumes from deep-sea vents in the Gulf of Mexico can reach up to 100 micromolar. A highly sensitive technique such as fluorescence spectroscopy may not provide the amount or quality of chemical specific data desired by the observer. However, a less sensitive technique such as Raman spectroscopy may be able nonetheless to detect those relatively high levels of methane AND provide chemical specific data regarding the methane and other chemicals present to an extent not provided by the more sensitive technique.
[0011] In this way, plumes of oil and gas in the oceanic water column can be detected from a substantial distance using a highly sensitive sensor and then characterized thoroughly using a less sensitive sensor.
[0012] An aspect of the invention also relates to an apparatus that can be used to perform the disclosed method.
[0013] For example, a dual optical spectrometer equipped with a pixilated detector such as a charge-coupled device, one or more light sources such as lasers, and one or more optical paths containing appropriate filters and other optical elements could be constructed such that: the spectrometer employs one laser chosen to be at a wavelength near the expected fluorescence excitation wavelength of the water column-interred oil and gas, one optical path with appropriate optical elements, and one portion of the detector to perform fluorescence spectroscopy; and the spectrometer employs one laser chosen to be at a wavelength away from the expected fluorescence excitation wavelength of the water column-interred oil and gas, one optical path with appropriate optical elements, and one portion of the detector to perform Raman spectroscopy.
[0014] Thus, this apparatus could be used to monitor "background" fluorescence of oil and gas in seawater. When that fluorescence is increased in intensity to some pre -determined level, the apparatus could be used to perform Raman spectroscopy of oil and gas in seawater. Alternately, both spectroscopies could be employed concurrently at all times, and the data merely viewed in light of the environmental conditions.
[0015] Another aspect of this invention relates the use of a method to increase the sensitivity of the second sensor, as described above, via amplification, pre-concentration, or multiple pass spectroscopic methods. Such methods include, for example, surface enhanced Raman spectroscopy methods and apparatus via use of plasmon amplification; ion-selective membrane pre-concentration methods and apparatus; and multiple pass spectroscopic methods via use of appropriate grazing angle, fiber, waveguide or other optics. In this embodiment, the invention would comprise a method and apparatus using a single sensor, e.g. a Raman spectrometer equipped with a liquid core waveguide and/or an optic coated with metal nanocrystallites, to detect and analyze chemicals in seawater.
[0016] The invention also relates to the use of an optical spectrometer to analyze materials dissolved or suspended in water columns at depths greater than 100 meters. The spectrometer is equipped with a special housing in order to withstand the pressures, temperatures, and corrosive fluids encountered at such depths. In one embodiment, the invention relates to using a Raman spectrometer packaged into a stainless steel housing. The spectrometer is used to analyze the quantity and type of hydrocarbons in the oceanic water column at 300 meters. From that data, hypotheses and conclusions regarding the geology, geochemistry, biochemistry, and other physicochemical properties of the surrounding water column, biological
communities residing therein, the seafloor below, and the subsurface sediments can be drawn.
[0017] Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 shows a schematic of a towed sensor platform with two sensors having different sampling paths in a housing; and
[0019] Figure 2 shows a schematic of a group of sensors attached to a remotely operated vehicle (ROV), the sensor housing may also be attached to a manned submersible or used by a diver to locate leaks near oil & gas platforms and pipelines; and
[0020] Figure 3 shows a schematic view of another embodiment where the sensors use one detector.
DETAILED DESCRIPTION OF THE DRAWINGS
[0021] In Figure 1 a towed array sensor platform is shown. In order to detect minute quantities of oil and gas in a plume, a fluorescent spectrometer 2 or the like is provided in the platform housing 1. The fluorescent spectrometer 2 is highly sensitive and can detect the minute quantities from a plume. Also provided in the sensor platform is a second sensor 3 which is less sensitive but provides greater detail in a chemical composition. The first sensor may be used to find the plume, while the second sensor 3 may be used to analyze the plume. The second sensor may be a Raman Spectrometer which can more readily characterize the chemical composition of the plume than the fluorescence sensor or spectrometer 2. In the platform shown in
Figure 1, the two sensors have different sampling paths to the platform housing. These sensors may also be used to monitor oil & gas plumes over time. As such they would be moored from a buoy or stationed in a sub-sea ocean platform.
[0022] Figure 2 shows another embodiment wherein several sensors may be located inside or outside a remotely operated vehicle (ROV) for leak- detection. The sensors may be accommodated into the same instrument housing and signals are stored in an onboard PC or sent to the surface through telemetry. The sensors may also have their own individual housings due to sample-instrument interactions or space constraints. The sensors may be rack mountable onto a manned submersible or designed with a smaller form factor and weight for use by divers. A sensor housing 11 may be located outside the ROV. Depending on the type of sensor a second sensor housing 12 may be located inside the ROV and communicate with a sample via an optical window or membrane 13 on the ROV. The ROV housing 14 can contain power supplies, an embedded PC memory and telemetry equipment 15.
[0023] Figure 3 shows another embodiment wherein one detector 4 is used. In this embodiment there are advantages to having a single flow path 5 through the platform housing. The two sensors employ two light sources 6, 7 of different frequencies. The first sensor may employ a fluorescence laser which may be chosen by wavelength to excite fluorescence in the sample. The second laser light source is chosen to have greater sensitivity to chemical compositions in the sample. Appropriate filters 10 and optical path elements 9 can be provided in order to manipulate the optical paths. One detector may be employed in the instrument which detects signals from the sample from each light source. This configuration may be used for the identification of plumes or leak detection.
[0024] As shown in figure 3 the sample pathway may contain filters 8 and/or adjustments in order to prepare the sampled water.
[0025] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.