Evaluating Conceptual Plays
107
an exploration risk that measures the probability of a prospect being
a pool. Estimating exploration risk in petroleum resource evaluation
is important. Methods for quantifying exploration risks are described
later.
Geological factors that determine the accumulation of hydrocarbons include the presence of closure and of reservoir facies, as well as
adequate seal, porosity, timing, source, migration, preservation, and
recovery. For a specifi c play, only a few of these factors are recognized
as critical to the amount of fi nal accumulation. Consequently, if a prospect located within a sandstone play, for example, were tested, it might
prove unsuccessful for any of the following reasons: lack of closure,
unfavorable reservoir facies, lack of adequate source or migration
path, and/or absence of cap rock.
The frequency of occurrence of a geological factor can be measured
from marginal probabilities. For example, if the marginal probability
for the presence-of-closure factor is 0.9, there is a 90% chance that prospects drilled will have adequate closure. For a prospect to be a pool, the
simultaneous presence of all the geological factors in the prospect is
necessary. This requirement leads us to exploration risk analysis.
Methods for Estimating Marginal Probability
When we assess a conceptual play, we begin by formulating a play defi -
nition. At this stage, a number of questions emerge:
Does the play in question exist?
•
Does the play have an adequate source?
•
Can we recover oil or gas from a play that lies under deep water?
•
Is the timing of hydrocarbon generation adequate for the play?
•
Table 5.1. Types of Evaluation Methods
Type of data available
Evaluation method
No data
Comparative geology
Types of source rock (conceptual
plays)
Types of expected products (oil, gas,
or heavy oil)
Stratigraphic columnar section
(conceptual or real)
Burial history, oil or gas window; timing
of generation
Areal extent and volume of source
rock
Petroleum system, material balance
107
an exploration risk that measures the probability of a prospect being
a pool. Estimating exploration risk in petroleum resource evaluation
is important. Methods for quantifying exploration risks are described
later.
Geological factors that determine the accumulation of hydrocarbons include the presence of closure and of reservoir facies, as well as
adequate seal, porosity, timing, source, migration, preservation, and
recovery. For a specifi c play, only a few of these factors are recognized
as critical to the amount of fi nal accumulation. Consequently, if a prospect located within a sandstone play, for example, were tested, it might
prove unsuccessful for any of the following reasons: lack of closure,
unfavorable reservoir facies, lack of adequate source or migration
path, and/or absence of cap rock.
The frequency of occurrence of a geological factor can be measured
from marginal probabilities. For example, if the marginal probability
for the presence-of-closure factor is 0.9, there is a 90% chance that prospects drilled will have adequate closure. For a prospect to be a pool, the
simultaneous presence of all the geological factors in the prospect is
necessary. This requirement leads us to exploration risk analysis.
Methods for Estimating Marginal Probability
When we assess a conceptual play, we begin by formulating a play defi -
nition. At this stage, a number of questions emerge:
Does the play in question exist?
•
Does the play have an adequate source?
•
Can we recover oil or gas from a play that lies under deep water?
•
Is the timing of hydrocarbon generation adequate for the play?
•
Table 5.1. Types of Evaluation Methods
Type of data available
Evaluation method
No data
Comparative geology
Types of source rock (conceptual
plays)
Types of expected products (oil, gas,
or heavy oil)
Stratigraphic columnar section
(conceptual or real)
Burial history, oil or gas window; timing
of generation
Areal extent and volume of source
rock
Petroleum system, material balance