ADVANCES IN RISKING EXPLORATION PROSPECTS

摘要

Assessment of prospect risk is a vital exploration activity, but technical literature on the subject shows few advances in methodologies in the last 20 years. Origin Energy has found that published procedures are not always adequate. Three perceived shortcomings are examined and techniques are proposed to overcome them. 1. Cases where prospect risk is dependent on reserve size. Traditional methodologies assume the two are independent This assumption is clearly inappropriate for, say, a prospect for which the success case value is based on the mapped closure, but which has suspect seal capacity that may limit the column height to something less than full-to-spill. A way forward is to build a variable risk array for a range of column heights and calculate the incremental risked NPV for each layer. The expected monetary value (EMV) is computed for a range of column heights based on the NPV of cumulative risked reserves; 2. Cases where the estimation of chance of success (COS) based on traditional geological information needs to be combined with direct hydrocarbon indicators (DHIs) from seismic data. DHIs are not infallible indicators, however, and cannot be used to set the COS for elements such as charge to say 100%. Bayes' Theorem can be used to combine the two sets of uncertain information. 3. Cases where prospects are risked on very limited data. Traditional risking does not adequately incorporate the level of knowledge on which risk assessments are made. Inadequacies are identified in existing methodologies, but no simple and satisfactory solutions can be identified. We do suggest a way forward, however, for a related problem—testing the sensitivity of the EMV calculation for an exploration prospect for uncertainties in COS.