High-resolution Surveys for Geohazards and Shallow Gas: NW Adriatic (Italy) and Iskenderun Bay (Turkey) |
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| Authors: | Daniel L Orange Ana García-García Dan McConnell Tom Lorenson Gary Fortier Fabio Trincardi Emrah Can |
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| Institution: | (1) Department of Earth Sciences, University of California, Santa Cruz, California, USA;(2) Marine Geoscience Division, Moss Landing, AOA Geophysics Inc., California, USA;(3) Marine Geoscience Division, AOA Geophysics Inc., 1300 W. Sam Houston Parkway South, Suite 225, Houston, Texas 77042, USA;(4) Coastal and Marine Geology Team, U.S. Geological Survey, 345 Middlefield Road, MS-999, Menlo Park, California 94025, USA;(5) El Paso Production, Nine Greenway Plaza, Houston, Texas 77046, USA;(6) Istituto di Geologia Marina – ISMAR (CNR), Via P. Gobetti 101, I-40129 Bologna, Italy;(7) Turkish Petroleum Corporation (TPAO), Mustafa Kemal Mahallesi, 2 Cadde No:86, 06520 Esentepe, Ankara, Turkey |
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| Abstract: | The need for quantifying and understanding the distribution of shallow gas is both of academic interest and of relevance to
offshore facilities. The combination of seafloor mapping, subbottom profiling, and multi-channel seismic data can provide
information on regions of possible shallow gas, where the gas impacts the acoustic properties of the host material and the
seafloor. In this paper, we present two case studies – one academic and one industry – that evaluate the distribution of shallow
gas in two field areas in the Mediterranean. In the first case study, geophysical data from Iskenderun Bay, southeastern Turkey,
indicate the presence and distribution of shallow gas. Pockmarks on the seafloor are associated with acoustic wipeout in the
shallow subbottom data. Although deeper seismic data do not show bright spots or other indicators of possible gas, instantaneous
frequency analysis clearly shows laterally restricted anomalies indicating gas-rich zones. The interpretation of possible
shallow gas resulted in moving a proposed drilling location to a nearby area characterized by fewer (but still present) shallow
gas signatures. In the second case study, cores acquired in the Po Delta, Adriatic Sea, provide quantitative ground-truthing
of shallow gas – as suggested by geophysical data – and provide minimum estimates of the percentage of gas in the subsurface.
Cores targeted on anomalous subbottom data yielded up to 41,000 ppm methane; cores with anomalous gas content are associated
with thick recent flood deposits which may effectively isolate reactive terrigenous organic matter from biologic and physical
re-working. |
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| Keywords: | shallow gas geohazards acoustic properties Adriatic Po Delta Iskenderun Bay southern Turkey |
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