Overpressure Zones and Shale Gas Exploration in SE Turkey

Abstract

In spite of negative environmental effects, the explorations of shale gas become very important and popular in the world to day, following important shale gas productions by American oil companies with horizontal drilling and hydrolic fracturing methods. In Turkey, many shaly formations, rich in organic matter contents, exist in SE Turkey and in the Thrace basin in particular. In SE Turkey, the principal shale gas units are firstly the Bedinan ( Ordovician-Silurian ) and Dadas ( Silurian-Devonian ) and secondly the Kastel and Germav ( Upper Cretaceous ) formations. On the other hand, it is well known that, a suture zone was occurred between the Anatolian and the Arabian plates during the Late Cretaceous and Miocene ophiolitic thrusts from north to the south. This suture zone continues from Hatay-Adiyaman to the Tpao-Perenco oilfields and towards to the Hazro area in SW-NE direction, while it is in NW-SE direction between Selmo and Celikli areas. During these tectonic events, due to the compressional forces, many high and abnormal pressure zones ( overpressure-geopressure ) occurred in the shaly sections in particular. Subsurface works and evaluations of Sonic ( BHC ) logs in the already drilled wells along the Suvarlı-Alidag-Selmo-Celikli line, parallel to the northern thrust line, indicate a similarity between the elongation of the suture zone and the development of the overpressure zones in the Bedinan, Dadas, Kastel and Germav shales. It has been observed that the overpressure zones migrate, like in the case of upwards migration of reefs during the geological times, towards higher levels in the stratigraphic column when approaching, from both sides, to the so called Hazro Arch ( curvature ). These overpressure zones create faults and fractures in the shaly formations, favorising unconventional gas productions from shales. Further to the south, around the Harman-Ambarcik-Dervishani- Köcek wells, the overpressure zones in the Bedinan and Dadas shales are oriented in E-W direction. With these subsurface works and results, obtained from the evaluations of Sonic ( BHC ) logs, it has been concluded that, the southern part of the Hazro Arch, shaped during the interplate actions between the Arabian and Anatolian plates, can be considered as an important shale gas exploration zone in SE Turkey.