Мурманская МИЛЯ. 2018 г. №4.

EXPLORATIONS Fig. 4 The map of 2D -4C survey performed by JSC MAGE in transition zone of the Priyamal part of the South Kara Shelf (left) and in the Pechora Sea (right) Рис. 4 Схемы расположения профилей 2D- 4C, выполненных ОАО «МАГЭ» в транзитной зоне Приямальской части Южно-Карского шельфа (левый рисунок) и Печорском море (правый) 54 vertical angles of inclination of the geophone axes with an accuracy of at least ± 2°. The maximum allowed depth of the station is 700 m which ensures its universal use. The tech­ nique of 2D-4C field seismic survey on the Arctic Shelf implies the use of three vessels: a base vessel, an arrangement vessel and a source vessel (Fig. 5). Array geometry depends on the CMP in­ terval specified by the project and the de­ signed nominal fold. In this case, the CMP interval was 25 m, and the interval of both source stake and receiver stake was 50 m. The shooting line was displaced by 50 m paral­ lel to the receiving line as at shallow depths the vessel could not move directly along the receiving line. The seismic survey was per­ formed via CMP method using centrally-sym- metric and single-ended spreads systems combined. The shooting was performed via air gun array designated for transit zones. The array consisted of one line composed of 5 GI-Gun 210 air guns with a total volume of 930 cu.in . (15 l). Navigation and hydrographic support of the works consisted in providing the naviga­ tor with navigational information during the deployment and shooting, surveying, and navigational data processing. The horizontal positioning of the geophysical survey points was carried out by means of the NAVSTAR navigation satellite system in the WGS 84 coordinates. C-Nav 3050 DGPS receivers in differential mode were used as receivers of satellite information on the vessels. To deter­ mine the vessels course, Geus gyrocompass and Trimble SPS-461DGPS receivers with a course determination option were used. Navi­ gation on the lines was carried out using the HYDROpro Navigation software. Daily changes in sea level fluctuations were measured by the MiniTide gauge. To tie the readings of the tide-gauge to the level of the geoid, the data of the level gauging stations were used. The horizontal accuracy of the geophysi­ cal survey points is ± 5 m; the RMS error of depths measurements is not more than 1% of the measured depth. As a result of the works, reliable seismic data were obtained for the four recording components. The H and Z components quality control was car­ ried out by the ProMAX R5000 and SeisWin QC software. The seismic survey performed by JSC MAGE allowed solving the geological tasks and obtaining new information on converted waves for reliable determination of the litho- logical properties of the sedimentary cover. The first results of the works carried out in the transit zone of the Pechora Sea and the Priyamal Shelf were proved success­ ful and provided us with high quality seis­ mic data (Fig. 6). The sections clearly show that the quality of the field data for the tran­ sit zone is comparable to the results of the standard shipboard seismic surveys. More­ over, the results of the work on the Priyamal shelf showed a high degree of informative value of the data for both the transit zone and coastal areas onshore work (Fig. 7). At the present time, at the time of “sanctions and import substitution”, our Company at its own expense is carrying out design and de- Fig. 5. Seismic survey technique using 4-component bottom systems in the shelf transition zone Рис. 5. Технология выполнения сейсмических работ с 4-компонентными донными станциями в транзитной зоне шельфа MURMANSK MILE • 4-2018