| Prospects of fiber optic techniques for shelf oil-and-gas fields surveying and monitoring |
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ZHEREBTSOV V.D., VINOGRADOV YU.A. Most perspective oil-and-gas-bearing structures in the Russian Federation are in the shelf and transitional areas, and only in 14% of these structures, the reserves are reliably evaluated with the help of 3D-geological-and-geophysical models, which allows the oilfields development stage to be initiated. Due to the absence of highly-effective exploration and monitoring systems in the RF, the rate of exploration works is low, making reserves replenishment unsatisfactory and oilfield monitoring of low quality.For about fifty years, the market of measuring systems and sensors applied in prospecting and monitoring of offshore deposits, has been dominated by electronic measuring techniques based on the conversion of measured parameters to electric signals which are further treated to electrodynamic, electromagnetic, piesoceramic ones, etc. At present, fibre-optic measuring (FOM) systems based on conversion of measured parameters to optical signals which are transmitted by optical fibre, are an alternative to the traditional approach [Zherebtsov]. Since the late 1990s, the leading foreign oil-and-gas companies BP, StatoilHydro, Shell, and others, in collaboration with military-industrial complexes of the USA, England, Norway have extended the application of conversion developments for marine geophysics in order to substitute traditional measuring complexes for FOM-systems characterized by significant economical, technical and ecological advantages [Terry Knott]. Full-scale tests of the prototype FOM-systems in 4D-4C surveying carried out by Stingray Geophysical in the North sea, in 2007, have shown that FOM-systems are highly effective in oilfield prospecting and have the oil-pool efficiency increased by 50%. Introduced, in addition to prospecting systems, are control-monitoring complexes based on the FOM-systems. These are used in the well hydrodynamic studies (temperature, pressure) and in the studies of the state of underwater pipelines. The advantages of FOM-systems used in acoustic-seismic monitoring of offshore zones are stipulated by the properties of the fibre-optic instrumentation such as bandwidth-duration; negligible losses in signal transmission, small diameter and mass of cable system; flexibility, mechanical strength; resistance to electromagnetic induction (and hence, the absence of hazardous events connected with lightning discharges, proximity to electric power lines, current pulses in power networks); explosion-proof; high insulation strength; high corrosion resistance, especially to chemical solvents, oils, fresh and sea water [Okosi T, et al., Kolomiets]. The FOM-systems development is related to the sphere of high technologies, envisaging wide use of nanotechnologies in making measurements, which is recently paid a special attention to in strategic national programs aimed at the scientific-and-technical potential development in Russia. Until 1992, Russia has been a leading nation in the field of development of fibre-optic measuring (FOM) techniques envisaged to solve the defense aims and some special-purpose applications. Over the next 15 years, neither these developments nor the domestic geophysical instrument-making industry based on standard (electrical) technology, have got any support, resulting in an essential lag from the leading maritime nations in this branch. Multi-component undersea measuring systems which are necessary in high-precision seismic survaying and shelf deposits monitoring, have not been developed in the former USSR on an extensive scale [5]. The entry of modern instrumentation with precision instruments and the FOM-systems components to the Russian Federation has not been admitted due to its possibility to be double applied. Therefore, in carrying out investigations on the Russian shelf, the Russian research vessels use the obsolete foreign seismic-and-acoustic instrumentation which is of little use in 3D-4D simulation and in detailed surveying of offshore deposits. The above said predetermines the actuality of establishing, on the basis of the scientific-and-technical backlog, which is still present in specialized scientific institutions (enterprises), the domestic manufacture of the FOM-systems in Russia. Innovative technologies introduced into the undersea geological exploration, will allow the seismic-and-acoustic surveying effectiveness to be improved 8-10 times, and 3D-oilfield models created to be more detail and accurate, which, in turn, will decrease exploration-drilling costs and decrease costs of oil-and-gas exploration by hundred billions roubles. Prospects and advantages of OFMT -application in the Barents shelf oil-and-gas fields seismological and seismic-and-acoustic monitoring.In accordance with the Concept of Geodynamic Safety in the Development of the Hydrocarbon Potential of the Entrails of Russia (2000), it is necessary to control the geodynamic regime in the zones of development of the Shtokman gas-condensate field (SGCF) and oilfields in the Barents sea shelf, as well as in the sites of undersea pipeline laying. For this purpose, a Seismic Monitoring Block (SMB) should be created to implement on-line monitoring of natural and man-made earthquakes within the area of oilfield commercial development, which is of particular significance for the SGCF region, within which, according to the preliminary evaluation, the induced seismicity can be of M=8-9 [5]. The SMB should reliably locate the earthquake hypocenters within the deposit’s, and the adjacent, area. The SMB should include two types of complexes to record seismicity: 1) On-Shore Complex – composed of on-shore seismic arrays (the Barents sea coast and islands), with functions similar to those of the pilot complex SAK “Apatity” [Vinogradov A.N., et al.], operated by the Kola Branch of the Geophysical Service, RAS since 1992; 2) Undersea Complex - based on OFMT, placed in the deposit and along the undersea main pipeline (МPL) . If properly invested, the on-shore complex equipped with standard instrumentation and software (for data acquisition and processing) tested by the KB GS RAS, can come to function in 1-2 years. It should be noted that within the Shtokman project area, the on-shore complex is capable to record events of only M=2,0-2,5, the Richter scale (Fig.1). This capability is far from being sufficient for guaranteed insurance of geodynamic safety of the objects of exclusive significance. Taking into account the above said, it is reasonable to place undersea seismic monitoring complexes to record micro-earthquakes of M<2 within the SGCF area and particularly along the MPL route which is characterized by the presence of land-slide-prone sites. The undersea seismic monitoring complexes based on multi-component FOM-systems are an optimal variant. The multi-component FOM-systems are capable to operate at different depths within the Barents sea shelf for 20-30 years, i.e. over the whole period of actual development of the SGCF, ensuring recording of super-low seismic-and-acoustic events. In addition, the undersea seismic monitoring complexes can be used in generation of 3-D sections to help control the stress-strain state of rocks within the SGCF area, provide on-line control over the change of pore pressure inside the pool in order to control its efficiency.. In addition to providing highly sensitive monitoring within the industrial sites, the undersea FOM-systems can be applied as on-line MPL-state monitoring systems. The linearly-distributed FOM-systems are characterized by considerable technical, economical and ecological advantages vs the traditional electric measuring devices applied at present by OAO GasProm [Zubkov A.I.]. In particular, measuring devices based on FOM-systems, can be extend up to 300km, being comparable in length with the most risk ground section of the Shtokman MPL. The main risks for off-shore structures are the following: The systems operated at present in the Russian Federation, and at OAO “GasProm” in undersea pipeline and the SGCF-structures on-line monitoring (the operation mode), do not ensure the necessary level of control of the risks mentioned. That is why, the perspective to improve the situation by application of spatially-distributed FOM-systems seems rather reasonable. Based on the above said, the authors consider it to be necessary to launch, in the Shtokman gas-condensate field, a special project whose aims are to introduce modern measuring complexes based on nanotechnologies, and improve the ecological and industrial safety in the SGCF development area. Being implemented, the project can promote effective development of the field. The objectives of the project are to create a new technology and new technical means to be used in seismic-and-acoustic surveying in oil-and-gas fields of the Russian Federation, in the frequency range of 0.2Hz – 15kHz, with a dynamic range of at least 150dB. The undersea multi-component system includes 120-240 seismic-and-acoustic channels, with the extension of the system on the basis of the module principle (to 3000-10000 channels) being possible. The main outcome of the Project will become the creation in Russia of a competitive undersea seismic-and-acoustic measuring system to be used in surveying and monitoring of oil-and-gas fields. These allow to effectively solve the problems of fuel raw materials base replenishment, at the expense of supplementary development of the oilfields decommissioned, and of new oilfields surveying, etc. The factors above determine the strategic significance of the Project for the Russian Federation. References Zherebtsov V.D. Marine geophysical optical-fiber measuring system // Procs. Of the Conference - Oil and Gas of the Arctic Shelf - 2004, 64p. |