Paleothermal Study of Triassic Formation in Syria by Using Fluid Inclusion

Ahmad Bilal

The last 10 years have seen great strides in applying fluid inclusions to many different fields, particularly oil prospecting, development of organic material, oil formation and migration, and determining thermal gradient. The Triassic sequence in Syria has not been observed on the surface, but deep-well data indicate it is a pyritic dolomite and radiolarian formation 1,200 m thick.

This study of fluid inclusions examined several hundred samples collected from different wells distributed throughout Syria. The results show the existence of aqueous, carbon, and hydrocarbon inclusions. Since aqueous inclusions vary in their common (form, distribution) and physicochemical properties (fusion temperature, homogeneity temperature, density, etc), a chronological relation could be made giving the following results: aqueous inclusions in the detritic minerals (type q₁) are prediagenesis, and aqueous inclusions related to overgrowth minerals (type q₂) are contemporary with diagenesis. But type q₃ aqueous inclusions in the secondary fractures that cross many minerals are postdiagenesis. Therefore, type q₃ inclusions are used to det rmine the temperature of Triassic formations, taking into consideration their saltiness (NaCl content is 10%, according to applied data). Carbon and hydrocarbon inclusions are postdiagenesis according to aqueous inclusion type q₂.

By using both the density of type q₂ aqueous inclusions and the heaviness of the rock overburden according to the depth of the samples studies, thermal gradient can be determined. It ranges between 5 and 7% and increases from the north-northeast toward the west-southwest, i.e., in the direction of tectonic anomaly and volcanic activity connected with the Great Syrian Rift, which is a continuation of the Great African Rift. In addition, thermal gradient increases with depth in every well but is mainly related to the location of the well according to the common trend mentioned above.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.