Multi-fault analysis scorecard: testing the stochastic approach in fault seal prediction

Abstract

AbstractMulti-fault analysis is an ExxonMobil stochastic tool for analysing the impact and sensitivities of stratigraphic uncertainty and variability on cross-fault leakage of hydrocarbons in faulted traps. This juxtaposition-based method provides quantitative prediction of hydrocarbon contact levels through a complex system of structural spills and juxtaposition leak points in traps with stacked reservoir systems and one or more faults. Validation of the Multi-fault analysis technology was carried out by comparing pre-drill predictions to post-drill results from 41 faulted exploration prospects drilled from 1994–2001. Of the 41 prospects, 29 were valid tests in which we made 22 successful predictions. Of the 22 successful outcomes, 11 were discoveries and 11 were dry wells. Some of the dry wells were drilled assuming the presence of sealing fault-zone material to trap hydrocarbons despite a Multi-fault analysis failure prediction. The seven Multi-fault failures comprise four predicted successes that were failures and three predicted failures that were successes. Most of the Multi-fault prediction failures can be attributed to data quality and uncertainty; however, some may be associated with sealing fault-zone material. Other considerations in fault seal analysis (i.e. dip leak along faults and sealing fault zone materials), model input uncertainties, and using drill-well learnings are also discussed.