Deep Seismic Exploration of the South Caspian Basin: Lithosphere-Scale Imaging of the World’s Deepest Basin
James H. Knapp, Camelia C. D. Knapp, John A. Connor, John H. McBride, Mike D. Simmons, 2007. "Deep Seismic Exploration of the South Caspian Basin: Lithosphere-Scale Imaging of the World’s Deepest Basin", Oil and Gas of the Greater Caspian Area, Pinar O. Yilmaz, Gary H. Isaksen
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The Caspian Sea basins of central Eurasia constitute one of the major petroleum provinces of the world. The tectonic setting and geological evolution of the South Caspian Basin remain enigmatic, particularly with respect to the generation of such significant hydrocarbon resources. Situated in the Alpine–Himalayan collisional zone, the Caspian Sea separates the locus of young continental collision in the Caucasus to the west from large-scale strike-slip faulting in the Kopeh-Dagh system to the east. Although the basin is thought to have originated in the Mesozoic, as much as 8–10 km (4.8–6 mi) of Pliocene–Pleistocene strata have accumulated, representing average depositional rates of greater than 1.5 km/m.y. (0.9 mi/m.y.) for the last 5 m.y. The presence of numerous gas-driven mud volcanoes and active oil and gas seeps suggests that hydrocarbons areforming and migrating within the basin today. Furthermore, active seismicity in the region attests that structures and associated hydrocarbon traps in the shallow section are forming now.
New deep normal-incidence seismic reflection data from the South Caspian Basin provide the firstfull crustal and upper mantle image of this basin. Collected as part of a 1998 acquisition program directed by Chevron Overseas Petroleum Inc., two roughly perpendicular deep seismic reflection profiles were acquired offshore Azerbaijan (Figure 1). These profiles, in the vicinity of the Apsheron Ridge, are each about 70 km (43 mi) in length and are recorded to 20 s in a key area for understanding the regional tectonics of the enigmatic Caspian Basin system. The main aim of collecting deep seismic data in this important petroliferous basin was to (1) reveal the deep structure and tectonics of the Alpine–Himalanyan continent– continent collisional zone beneath the South to Central Caspian Sea; (2) portray the full Mesozoic(?)– Quaternary section of the sedimentarybasin that is inferred to be, in places, thicker than 20 km (12 mi); and (3) elucidate the thickness and nature of the crust, providing critical information for subsidence and thermal modeling, with implication for source rock maturation. These new reflection data provide a pseudo-three-dimensionalarchitecture of the South Caspian Basin in the vicinity of the Apsheron Ridge. Although recorded with standard industry parameters (airgun source of 52,111 cm3 [3180 in.3] at 1900 psi [13 MPa], 25 m [82 ft] hydrophone spacing, 5100 m [17,716 ft] streamer length, 4 ms sample rate), the two deep seismic lines provide an image of the basin down to the upper mantle depths.
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Throughout time, the greater Caspian area has maintained its position as one of the major petroleum provinces in the world. Its early history as a prolific producer of oil is well known. Caspian region exploration dates to the seventh century B.C., during the time of the Median Kingdom in today's southern Azerbaijan. Oil played an important role in the everyday lives of these ancient tribes of the region, and it is still a very important commodity today. The past two decades have seen many important advances in our knowledge of the geological evolution of hydrocarbon-bearing sedimentary basins. The success of modern exploration is, to a large extent, based on new advances in both deep and 3-D seismic imaging, as well as improved pressure-prediction and pre-drill oil and gas quality predictive methodologies, to mention just a few. Nevertheless, large areas of the greater Caspian region have remained unexplored due to a variety of factors such as deep-water conditions and zones with high pore-pressures in the South Caspian Sea and The Black Sea, and vast shallow-water regions with harsh winter ice conditions in the North Caspian Sea. This publication contains 12 extended abstracts and 6 full-length papers that discuss technology development, challenges in estimating proven and potential reserves, outcrop-based studies of potential reservoirs, regional tectonics and geodynamic evolution, and source rock and stratigraphic analyses of the greater Caspian area.