UNCONVENTIONAL EXPLORATION IN SE TURKEY - AN EXECUTIVE SUMMARY
The unconventional exploration idea in Dadaþ hot shale and in Bedinan tight sandstone is new for Turkey. The subject is also new in the world as well!
In SE Turkey, 745 exploration wells have been drilled by TPAO alone (till 2008), all the wells were focused mainly on Conventional Exploration in the Cretaceous Mardin Carbonates or younger formations not in the Paleozoic Formations, however nearly 75 wells in Districts-X &-XI have reached the Lower Paleozoic rocks of Bedinan tight sandstone and/or Dadaþ shale. Some well tested oil/gas in the in those formations but due to low permeability and porosity problems they were non productive. Since 2010 TransAtlantic, Valurea and Shell-TPAO JV companies are working on unconventional exploration in SE Turkey. Only one well (Göksu-1R well) re-entered and fractured in the Dadaþ-I hot shale, some non economical gas was tested by TransAtlantic.
In 1985, several wells had been fractured in the Eocene aged Hamitabat Sandstone (not in the shale) in the Hamitabat Gas Field by TPAO in the Thrace Basin. The gas production in the Hamitabat sandstone was folded 5-10 times. Also since 2010, TransAtlantic has been fracturing Mezardere and older shales in the southern Thrace Basin, in some wells gas production has been increased 4-7 folds.
The main Lower Paleozoic formations are good candidates for unconventional exploration those are; Ordovician; Bedinan tight sands and Lower to Upper Silurian Dadaþ shale, mainly in Dadaþ-I hot shale member.
Bedinan tight sandstone is the most widely distributed Lower Paleozoic rocks in the basin. The formation covers entire northern extension of the Arabian Plate, except over the Mardin high. The Formation has been divided in four members by TPAO; Bedinan-I (at the bottom), -II,-III, and – IV (at the top), the thickness of those are 160-850m, 435-645m, 613-790m and 230-290m, respectively
Bedinan-I: made of dark shale, has gas generation potentials, only few wells penetrated the member.
Bedinan-II: made of siltstones and tight ss and some shale have limited gas generation potential, only few wells penetrated the member.
Bedinan-III: made of sandstones and shale alternates, sand porosities reach up to 20%, only few wells penetrated the member.
Bedinan-IV: made of sandstones, siltstones and shale, sands have some reservoir potentials. More than 72 wells have penetrated the member.
In SE Turkey nobody has studied or published the Bedinan tight sandstone in detail enough for the tight sand (basin center gas) unconventional purposes. It has been reported that the lower members of I and II has good shale and the upper members III and IV interbedded with tight sandstones and shale members that may be good candidates for basin center gas. See the figure below:
Paleozoic Section In SE Turkey
After Bozdoðan at all, 1994, 10th Petroleum Congress
Dadaþ Formation was only deposited on the northern areas of Districts- X I& –X. Only Dadaþ-III member has exposed west of Hazro Town, north of Diyarbakýr. The formation has limited subsurface extension around Diyarbakýr; 75km in N-S direction and 150km in E-W direction. It covers of an area of 11,250km2 (2.8 million acres). Dadaþ extension is shown in the below figure.
Paleozoic Units Stratigraphy and Correlation in SE Turkey
The Dadaþ Formation has been divided three members by TPAO, which is based on lithological and biostratigraphic characterizations; Dadaþ-I (the lowest member) the hot shale member, Dadaþ-II and Dadaþ-III. GR logs have unique responses for the members and can be easily identified. Dadaþ deposits filled the irregular topography of the older Bedinan basin. It is a regressive section and generally thickness towards to the North. Within the Dadaþ there are some several small sub-basins.
Dadaþ-III member is the top member and made of shale, marl, sandstone, dolomite and limestone. It was deposited in high energy shallow marine environment. Maximum thickness was recorded 112m. Dadaþ-III may have limited source rock potential in District-X, near the town of Hazro.
Dadaþ-I member is mainly deposited on the eroded Bedinan surfaces in the low areas. The member is not exposed anywhere in SE Turkey and is only cut in the wells. It is best hot shale, high TOC and matures towards to lower section.
About 72 wells penetrated Dadaþ and Bedinan Formations however, only few wells cut the full section of the Dadaþ Formation. The Dadaþ-I member is the best source rock potential (hot shale) in SE Turkey. It was deposited in deep marine, low energy anoxic environment. The TOC values run between 0.5-10% and VRo value runs 0.7-5%. The thickness ranges between 0-250m.
Time Oil Migration
In SE Turkey one of the most important factors affecting the HC generation is the thickness of the overburden formations and the maturation of the source rock (hot shale). When the Dadaþ hot shale is minimum 25m of thickness and covered by 2,500m thick of over burden rocks for a longer period it can potentially be a mature source rock. It has been proved that H-C generation started immediately after the emplacement of Cretaceous thrusting over the Dadaþ source rocks and H-C generation may have started from the end of Early Cretaceous to Paleocene.
Dr. Sezgin Aytuna
Consulting Unconventional Exploration Geologist, Ankara