Source rock: the first key element of a petroleum system

A petroleum system is the set of all the elements and processes involved in the formation of petroleum accumulations in sedimentary basins. Even if many efforts are usually made in localizing reservoirs and traps and in understanding their structure and properties, it has been proven that almost no petroleum accumulation would exist without source-rock. Source-rocks, by their distribution and properties, are directly responsible for the quantity of petroleum to be considered in the system. Source-rock reactivity also controls the timing of petroleum generation, which can lead to failure if not well accounted for due to the absence of trap at the moment of the migration of petroleum. Lastly, source-rock properties and maturity gives some insight on the quality of the hydrocarbon products which can be found in the reservoirs what is of primary importance for the economical evaluation of a prospect.

In oil and gas exploration, the petroleum potential of a source rock, generally characterized by its thickness and its total organic carbon (TOC) and hydrogen index (HI), is then of primary importance. Therefore, explorationists must estimate the distribution of source rock richness (TOC and HI) and reactivity. During operational petroleum exploration projects, estimation of source-rock distribution is generally obtained from scarce field data (e.g. well data or outcrop) and then mathematically extrapolated (e.g. simple kriging or smoothing methods) to the whole basin hardly including the available geological information. If these methods can prove to be useful, but not always satisfactory for accurately identify sweet spots, for unconventional resources as many wells target the source rocks, this is far to be the case in conventional exploration.