Looking for Hydrocarbons in Dry Holes - Application of Fluid Inclusion Chemistry in North Africa/Mediterranean

Fluid inclusions can provide hard evidence for the presence of hydrocarbons in a ‘dry’ hole and fluid inclusion screening of cuttings forms a routine part of a dry hole analysis in many oil companies. Subsequent microscopic and chemical analyses provide additional compositional information via cryo-optical and quantitative fluorescence techniques, constrain the timing of migration or reservoir filling (from paired analyses of coeval petroleum and aqueous inclusions) and can identify the source of the hydrocarbons via GCMS and/or isotopic methods. A particularly useful technique is compound specific isotope analyses (CSIA) of the gas components of the fluid inclusions. For instance, in many basins in North Africa and the Mediterranean, there is uncertainty about the presence of the Silurian Tannezuft (Qusaiba) source rock. This source rock was deposited after the Silurian deglaciation and source rock quality depends on the anoxia and stratification of the water column, which varied regionally with the topography at that time of deposition. With CSIA analyses of fluid inclusions, the presence of Silurian generated gas is easily recognized from the carbon isotopes that are characteristic for the Silurian generated gases. In this presentation, we describe recent applications of the fluid inclusion geochemistry from Libya, Syria and Oman.