Summary
Prospects in a common basin are likely to share geologic features. For
example, if hydrocarbons are found at one location, they may be more likely to
be found at other nearby locations. When making drilling decisions, we should
be able to exploit this dependence and use drilling results from one location
to make more informed decisions about other nearby prospects. Moreover, we
should consider these informational synergies when evaluating multiprospect
exploration opportunities. In this paper, we describe an approach for modeling
the dependence among prospects and determining an optimal drilling strategy
that takes this information into account. We demonstrate this approach using an
example involving five prospects. This example demonstrates the value of
modeling dependence and the value of learning about individual geologic risk
factors (e.g., from doing a postmortem at a failed well) when choosing a
drilling strategy.
Introduction
When considering a new prospect, it is important to consider its probability
of success. In practice, this assessment is often decomposed into success
probabilities for a number of underlying geologic factors. For example, one
might consider the probabilities that the hydrocarbons were generated, whether
the reservoir rocks have the appropriate porosity and permeability, and whether
the identified structural trap has an appropriate seal [see, e.g., Magoon and
Dow (1994)]. The overall probability of success is the product of these
individual probabilities. Although these assessments may be difficult, for a
single prospect, this risk analysis process is straightforward.
When considering multiple prospects in a common basin or multiple target
zones in a single well, in addition to considering the probability of success
for each prospect, we need to consider the dependence among prospects. For
example, if hydrocarbons are found at one location, they may be much more
likely to be found at another nearby location. Conversely, if hydrocarbons are
not found at the first location, they may be less likely to be found at the
other. When evaluating opportunities with multiple prospects, we should
consider decision processes and workflows that exploit this dependence and use
results from early wells to make more informed decisions about other locations.
For example, if a postmortem analysis of core samples from a failed well
reveals that there were no hydrocarbons present, then we may not want to
continue drilling at nearby sites. On the other hand, if the postmortem
analysis reveals that hydrocarbons were present, but the reservoir lacked a
seal, then we may want to continue to explore other nearby sites. In this
paper, we describe an approach for modeling dependence among prospects and
developing a drilling strategy that exploits the information provided by early
drilling results.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
27 June 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
27 May 2007
- Manuscript approved:
19 October 2007
- Version of record:
25 April 2008
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