Assessing combination traps: using risk to define uncertainty

Probabilistic assessment of exploration prospects comprises two processes: estimation of risk, and estimation of uncertainty. Risk, R, is the chance of failure, while 1-R is the chance of success. Uncertainty is the range of volumes, and their associated exceedance probabilities, that we may encounter if we are successful. The chance of success is often impacted by the trap type. Fault-dependent closures are usually perceived as having lower chances of success than fault-independent closures. Combination traps, i.e., traps that are both fault-independent and fault-dependent, require a blurring of the distinction between uncertainty and risk. The chance of success for each trap type is used to define the uncertainty within the success case. In order to create the success case distribution of potential contacts in a combination trap, one must consider the chance of success for each individual trap type. Geologists who do not consider risk when assessing uncertainty may create success case distributions that cannot be technically supported.