How a Puzzling Set of Geological Features Challenge Hydrocarbon Exploration in the Black Sea Basin
Abstract
The Black Sea basin is one of the last exploration frontiers close to European market; however, it is still immature one despite of 40 years of exploration efforts bearing high share of geological risk. Unfortunately, the advance of modern ultradeep drilling to the basin did not resolve the problem yet, so no one giant hydrocarbon field or equivalent trend of smaller ones is discovered to the date in the basin despite of its size and some promising characteristics. An ambiguity in understanding of the Black Sea basin tectonistratigraphic structure and evolution as well as its petroleum systems (source rocks quality and reservoir rocks areal distribution) coupling with socio-economic factors hampers timely development of this petroleum province. As to geological obstacles postponing an anticipated exploration success, these are as follows.
Most of the basin area is a deepwater domain with 1000-2200 m of water column so its exploration requires significant long-term capex investments into seismic surveying, drilling and field development;The basin lacks reservoir rocks and their spatial development is very uncertain; to find high quality reservoir is quite equal to discover a hydrocarbon field;Low heat flow is characteristic of the basin limiting due organic matter maturation at the depth testable by routine drilling using jack-up platforms; only the circum-Black Sea transition zone from continental to oceanic crust reveals suitable maturation values in some places;The Black Sea basin has dissipated its initial thermal impulse during synrift and drift stages for intense volcanic activity without secondary rejuvenation, moreover, an extra lithospheric plunging due to steady approaching of the Arabian plate to Eurasia affects its domain since Oligocene time;Except of the Maykop source rocks (and Mid-Eocene and Sarmatian ones with some limitations) all other potential intervals demonstrate suitable generation parameters only sporadically and the basin is mainly considered as predominantly gas-bearing one charged with mixed biogenic-thermogenic methane;Anomalous thickness of Pleistocene-Holocene sediments, submarine canyons and slides, as well as local presence of gas hydrates and mud volcanoes complicate geotechnical exploration conditions within the continental slope and depocentral part of the basin; an abnormally high formation pressure in many deepwater localities is a challenging factor;Mainly peripheral tectonic inversion and absence of evaporitic sequences (there is evidence for the Messinian unconformity only) have limited basinwide development of high quality sealing and entrapment for migrating hydrocarbons although the Black Sea is one of the gassiest basins in the world;Peripheral uplifts like the Marginal Terrace, Tetyaev and Shatsky swells, Polshkov and Druzhba highs as well as buried front of Pontides have captured a clastic sedimentary flux from the landmasses from time to time that limited a basinwide reservoir rocks distribution.null
It is necessary to add to this that environment of this semi-closed water basin is extremely vulnerable and unsolved problems with delimitation of economic zones in some sectors of the Black Sea retain political risks for its hydrocarbon exploration.
AAPG Datapages/Search and Discovery Article #90226 © 2015 European Regional Conference and Exhibition, Lisbon, Portugal, May 18-19, 2015
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