AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geochemical Characterization of Outcrop Samples from the South Caspian Basin, Eastern Azerbaijan: The Value of a Multidisciplinary Approach in Understanding Petroleum Source Intervals
(1) Subsurface Technology, ConocoPhillips, Houston, TX.
(2) Geology and Geophysics, University of Utah, Salt Lake City, UT.
(3) Azerbaijan National Academy of Sciences Geology Institute, Baku, Azerbaijan.
Fine-grained Paleocene-Miocene strata of eastern Azerbaijan record the evolution of the South Caspian Basin from an open marine system, which was well-connected to the Tethys Sea, to an isolated epicontinental sea. Additionally, these strata form the main source interval for the major hydrocarbon accumulations locally and throughout the Caspian region. Four hundred Paleocene-Miocene samples collected within eastern Azerbaijan demonstrate spatial and temporal geochemical heterogeneity within the predominately mudstone succession. This study compares our previously published inorganic geochemical evaluation of these samples using trace metals, bulk composition, and stable isotopic ratios to newly aquired organic geochemical data in order to better understand the basin evolution and hydrocarbon generation potential of this interval. Sample TOC values range from 0.3 to 6.3%, with Oligocene-Miocene Maikopian samples showing average values of 1.4%, compared to lower TOC values found in Paleocene-Eocene strata (average = 0.3%). Rock-Eval pyrolysis of 79 samples shows that the majority of strata are organic lean, immature, and mixed oil/gas to gas prone, with a smaller group of latest Eocene-Early Miocene samples having better oil prone source potential. The majority of strata, even within the Oligocene-Miocene Maikopian interval, are not classic Type II oil-prone source rocks. The majority of oil generation appears to come from thin, discrete intervals of good oil-prone source character, while the large remaining volume of organic-lean, Type II/III to Type III source rock facies makes it a potentially significant gas source. Analysis of the often discounted Paleocene-Eocene source interval suggests that further gas generation may have come from this older, more thermally mature interval. Gas chromatography and biomarker analysis of 24 samples reinforces the thermal immaturity of most samples, shows varying levels of terrestrial input, and suggests that well-oxygenated waters prevailed with periodic suboxic to dysoxic/anoxic events depositing more oil-prone strata. The pairing of inorganic and organic geochemical data highlights gross differences between the Paleocene-Eocene and Oligocene-Miocene stratigraphic intervals, and show that, although chemostratigraphic correlations can be made across the study area on the large scale, spatial variation in source rock character is significant.