Timing as a Vital Element of the Petroleum System: Use of Thermal History Reconstruction Using AFTA® and VR as a Route to More Efficient Exploration

Abstract The timing of hydrocarbon generation with respect to trap formation is clearly a vital element which can critically affect the prospectivity of a region. Understanding timing issues is also important in evaluating factors controlling the destruction and preservation of oilfields. Curiously, this aspect of timing in the petroleum system often seems ignored, perhaps because conventional techniques typically cannot provide a direct estimate of the timing of a thermal episode or in some cases, of multiple events. Using a series of case studies in different tectonic settings, we show how Thermal History Reconstruction (THR) using Apatite Fission Track Analysis (AFTA®) and vitrinite reflectance (VR) can be used to identify, quantify and characterise the major thermal episodes (related either to deeper burial, increased heat flow, hot fluid movements or igneous activity, or some combination of these processes) which have affected a sedimentary basin. Application of THR results in a reconstructed maturation history constrained by measured data, in particular with firm definition of the timing at which hydrocarbon generation ceased. In basins where maximum maturity levels were reached some time in the past, this vital information, which plays a crucial role in determining hydrocarbon prospectivity, may not be available from other methods. Using this approach, more efficient exploration is possible, by focussing on the most viable plays.