Sub-surface model predictions and regulatory requirements*

Abstract

In recent years, the construction of sub-surface models to understand complex systems has become almost ubiquitous. At the same time, societies have become more litigious and governments in the Asia-Pacific region have become more demanding in their technical requirements for exploration and development approvals. But most experienced geoscientists that really understand the capabilities of these models are much more sceptical about the predictive capability of reservoir modelling and acknowledge that even their best models are either highly subjective or quantified guesses.

If reservoir models provide technical justification for investment decisions or, especially in the case of CO₂ sequestration, decisions that may face future litigation, then it is important to be able to quantify their capabilities and to place reasonable limits on the expectations of these models. The simple question, ‘What is a good reservoir model?’ raises many different answers from a group of geoscientists, and yet if we are not clear on what a good model is, how can we conceptualise better models as distinct from worse models? Without clear guidelines for good models it is difficult to determine who is qualified to build a model or who is qualified to audit a model. In this situation, if authorities continue to increase their demands for models to support reservoir management decisions, then many months of effort will continue to be wasted in the construction of models with no numerical validity or predictive capability.

One of the aims of this paper is to open discussion on these issues and to suggest areas where clear consensus needs to be established for the benefit of the industry, the Government and our society. Uncertainty in structural interpretation and uncertainty in deposition have a significant impact on good reservoir management for individual companies and on the wise management of national resources. The application of good modelling practices and appropriate validation by regulatory authorities is a sensible aim for our industry and one that has been overlooked for too long.