Assessmemt of hydrocarbon potential of uplift structures in sedimentary basins from their geological history (Ateshgah structure in Baku Archipelago)

Abstract

The accumulated content of organic matter in a sedimentary basin strongly depends on the geological conditions of its formation, in particular, on the deposition rate according to geological epochs. Lithological and stratigraphical cross sections and other available relevant geological data allow us to reconstruct paleographic profiles of a structure, for example, a fold or uplift, for different time periods. From the reconstructed paleoprofiles (backstripping technique), the rates of the fold development and deposition rates for past geological epochs can be approximately assessed. We try to establish the potential of relevant lithological units as source rocks for hydrocarbon deposits, determining the rates of sedimentation for several time spans of the geological history of a hydrocarbon-bearing structure. As case study, Ateshgah uplift is considered as a large offshore anticline structure in the central part of Baku archipelago in the Caspian Sea. Fold growth rates for this structure steadily increased throughout the time from the rate of 0.3¾0.4 km/mln yr by the beginning of Paleocene eventually reaching the values of 0.5¾1.3 km/mln yr. This result is in agreement with similar paleographic reconstructions, recently reported for other prospective structures in the region. The deposition rate of sediments generally increased with time with certain variations following the changes in the paleogeography. There is a certain threshold value of the deposition rate, below which the structure is not capable of producing/accumulating hydrocarbon matter in substantial or commercially interesting amounts. This observation can be used as a rule of thumb for linking the reconstructions of the structure development with the anticipations about its hydrocarbon potential. With the exception of Paleocene and Eocene, the remaining stratigraphic intervals in the structure were favorable for the accumulation of organic matter in potential mother rock at least exceeding the Clarke number.