--> A Multiple Model Technique for Evaluating the Potential Hydrocarbon Volumes and Risk of an Exploration Prospect, by Chris Swarbrick, Robert Kimmel, Steve Jenkins, Peter Leiggi, and P.M. (Mitch) Harris, #40291 (2008)

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A Multiple Model Technique for Evaluating the Potential Hydrocarbon Volumes and Risk of an Exploration Prospect*


Chris Swarbrick1, Robert Kimmel2, Steve Jenkins3, Peter Leiggi4, and P.M. (Mitch) Harris4


Search and Discovery Article #40291 (2008)

Posted July 21, 2008


*Adapted from oral presentation at the 2006 AAPG International Conference and Exhibition, Perth, Australia, November 5-8, 2006.

Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.


1 Chevron Australia Pty Ltd, Perth, Australia.

2 Chevron International Exploration & Production Bellaire, TX ([email protected])

3 Chevron Corporation, San Ramon, CA ([email protected])

4 Chevron Energy Technology Company, San Ramon, California, USA ([email protected])



The potential hydrocarbon volumes and geologic risk of an exploration prospect are usually assessed by constructing a single geological model describing the likely structure, reservoir, seal and hydrocarbon charge. However, a single model often does not adequately capture the wide range of alternate geological models which could exist within the constraints of available data. Though the probability of these other models occurring may be relatively small, their impact on the probabilistic distribution of potential hydrocarbon-in-place volumes may be large.

To assess potential hydrocarbons volumes and geologic risk of a Paleozoic carbonate buildup in the southern PreCaspian Basin, Kazakhstan, suites of possible reservoir and possible seal models were developed in an attempt to adequately describe the full spectrum of potential reservoir and seal scenarios which could exist within the data constraints. A workflow was then followed comprising a) estimation of the probabilities for each reservoir-seal combination, b) calculation of volumes for each combination, and c) generation of a cumulative probability curve relating resource volumes to their probability of occurrence. Model probabilities were used to calculate the appropriate geologic risks for reservoir and seal failure.

We found the multiple model technique is very effective in capturing, evaluating, and ranking a wide range of geologic concepts and divergent expert opinions. The technique has the additional advantage that the calculated risk incorporates all possible outcomes, not just the risk associated with a single geologic model. We believe the multiple model technique can be applied to other prospects which have a wide range of geologic outcomes for two or more key play elements.



Selected Figures

The prospect.

Why use the multiple model approach? a) Prospect evaluation has reached the “Drill/No Drill” decision point; b) differences of opinion regarding potential resource size and geologic risk; c) alignment needed on seals and potential column heights, reservoir parameters and their spatial distribution.

Range of seal models. Potential HWC is controlled by saddle stratigraphy.

Probability ranking of seal models incorporating local and regional field data and analogs.

Range of reservoir properties. Selected regions of nearby fields were used to capture the likely range of depositional facies, diagenesis, porosity, and permeability.

Probability ranking of reservoir models incorporating local, regional, and analog data.

Scenario volumetrics, as a cumulative probability distribution plot.



  • Use of multiple conceptual models recognizes the uncertainty common in geological interpretations.
  • Probability weighting of volumetric outcomes provides a representative resource distribution curve which incorporates intermediate success cases.
  • Model probabilities can be used to estimate geologic risks.
  • Geologic risking is based on a range of possible outcomes, not just the chance of success for a single model.
  • The Multiple Model approach can help achieve alignment among groups with diverse interpretations.


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