Abstract

Prospect appraisal in the Shell Group uses a flexible system with options applicable to areas with different hydrocarbon habitat and data availability.

The system is probabilistic and quantifies uncertainties and risks. Volumetric estimates are given as expectation curves. It is applicable to single prospects or leads, structural or stratigraphic, to single, multi-layered or stacked reservoirs.

In the most sophisticated option, PAQC (Prospect Appraisal by Quantitative Calibration), the following processes are quantified by simulation using simplified numerial models.

Generation     )
Primary migration/explusion ) Charge
Secondary migration   )
Accumulation
Retention

The models for charge volumes and retention capacity (with standard deviation) as well as the probabilities of HC charge (oil and/or gas) and retention are based on a worldwide calibration.

There are additional options for areas with excess charge and for areas where quantification of charge parameters is tenuous.

In a different branch of Shell's sytem, PADE (Prospect Appraisal by Direct Estimate), charge and retention are quantified by a probabilistic estimate of the length and composition of the HC column. It is especially designed for areas where statistical data on HC columns are available and can serve as a local calibration set. There are additional PADE options for drilled prospects and for prospects with direct hydrocarbon indicators.

For a consistent and systematic approach, appraisals are preferably made using specialised interview teams of experienced geologists. An annual review of predictions versus actuals for all exploration wells drilled in the Group, monitors the validity of the appraisals especially as regards the geologist's quantification of the geological/geophysical parameters and risks.