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Risk Analysis in Unexplored Areas: Application of a Response Surface Model Based Tool on the Canadian Offshore

Abstract

Coupling the evolution of thermal and pressure regimes through time, petroleum system modeling is recognized as a key tool to estimate source rock maturity and hydrocarbon expulsion timing in unexplored basins. However, most of the data used in such basins is subject to uncertainty which becomes critical in frontier areas where very little information is available for calibration. The potential range of variation of input parameters leads to a high variability of the basin modeling simulation results and there is definitely a need for sensitivity and risk analysis in such studies. Traditionally, risk assessment is done performing multi-realizations with a Monte-Carlo sampling which requires a lot of time, sometimes months, when hundreds of simulations are required on a high resolution model. To overcome these delays unaligned to the E&P industry constraints, we here present a new workflow linking basin modeling to a dedicated uncertainty analysis tool based on response surfaces. If the later technology is commonly used in reservoir engineering, it is quite unknown in exploration. In this approach, a set of simulations – the experimental design – is used to compute response surfaces that provide very fast estimations of the simulator outputs for any parameter values. The uncertainty study is then conducted from the response surface predictions only. A limited number of simulations is generally sufficient to obtain reliable estimations. The total time required to estimate the risk associated to the model uncertainties is thus drastically reduced. The passive margin offshore Canada is used to illustrate this workflow. The focus is made on the deepest Jurassic source rock and the uncertainties linked to its maturity assessment as well as its petroleum potential: depth, surface temperature and basal heat flow variations, initial TOC and HI, etc. Two calibration wells available on the platform are used in the study. A sensitivity analysis is first performed to identify the most influential parameters in the different areas of the basin. A propagation is then realized to estimate the risk on the source rock maturity, the expulsion timing and expelled quantities. Applied to the full source rock unit and not only at a single well location, this approach provides relevant probability maps critical in the decision-making process.