Changes

#: If the map shows an antithetic fault closure, then what is the probability that such a structural configuration will actually turn out to be present?

#: If the map shows an antithetic fault closure, then what is the probability that such a structural configuration will actually turn out to be present?

#: This geological chance factor is formulated to apply to stratigraphic as well as structural traps, and in tacit acknowledgment that the structural map is ordinarily the single most important map involved in most prospects and many development projects. Also, structural "busts" are a common reason for dry holes.<ref name=Rose_1987>Rose, P. R., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0001/0000/0001.htm Dealing with risk and uncertainty in exploration--how can we improve?]: AAPG Bulletin, v. 71, n. 1, p. 1-16.</ref>

#: This geological chance factor is formulated to apply to stratigraphic as well as structural traps, and in tacit acknowledgment that the structural map is ordinarily the single most important map involved in most prospects and many development projects. Also, structural "busts" are a common reason for dry holes.<ref name=Rose_1987>Rose, P. R., 1987, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0071/0001/0000/0001.htm Dealing with risk and uncertainty in exploration--how can we improve?]: AAPG Bulletin, v. 71, n. 1, p. 1-16.</ref>

#: The geological structure chance factor, in combination with the reservoir requirement, focuses on the geometry of the envisioned oil or gas accumulation and on the volumes of fluids necessary to sustain a production test or prudent drill stem test.

#: The geological structure chance factor, in combination with the reservoir requirement, focuses on the geometry of the envisioned oil or gas [[accumulation] and on the volumes of fluids necessary to sustain a production test or prudent drill stem test.

# ''What is the probability (or confidence) that hydrocarbons are present in the subsurface geological environment such that the prospect has had access to them in some quantity to provide at least some modicum of '''hydrocarbon charge?'''''

# ''What is the probability (or confidence) that hydrocarbons are present in the subsurface geological environment such that the prospect has had access to them in some quantity to provide at least some modicum of '''hydrocarbon charge?'''''

#: This geological chance factor deals with such questions as the volumetric adequacy of petroleum source rocks, the generation of oil and/or gas, the migrational pathways to the site of the prospect, and the concentration of hydrocarbons in the reservoir fluid (hydrocarbon saturation of at least 50% is required). The question of timing is ''not'' addressed here. In most frontier basins, the hydrocarbon charge issue is very important. In established basins and producing trends, however, its significance tends to be slightly diminished. Obviously, for development projects, the hydrocarbon charge requirement has ordinarily been satisfied.

#: This geological chance factor deals with such questions as the volumetric adequacy of petroleum source rocks, the generation of oil and/or gas, the migrational pathways to the site of the prospect, and the concentration of hydrocarbons in the reservoir fluid (hydrocarbon saturation of at least 50% is required). The question of timing is ''not'' addressed here. In most frontier basins, the hydrocarbon charge issue is very important. In established basins and producing trends, however, its significance tends to be slightly diminished. Obviously, for development projects, the hydrocarbon charge requirement has ordinarily been satisfied.

==Probability of completion==

==Probability of completion==

The key question for most development geologists is, "What is the probability that this well will be completed?" Thus, the ''probability of success,'' or ''P''_s, is really the ''probability of completion.'' The probability of geological success (as defined and derived above) can be made to approximate the probability of completion (or the probability of success) by two linked measures:

The key question for most development geologists is, "What is the probability that this well will be completed?" Thus, the ''probability of success,'' or ''P''_s, is really the ''probability of completion.'' The probability of geological success (as defined and derived above) can be made to approximate the probability of completion (or the probability of success) by two linked measures:

# Minimum but finite dimensions are required for all reserves parameters, such as area, net pay, and hydrocarbon recovery factor. The concept here is that a small but finite volume of oil or [[natural gas]], and some minimum reservoir thickness and quality, must be present for an accumulation even to be ''detected'' by an operator. In other words, the lower limit of an ''accumulation'' thus defined is substantially larger than 1 bbl of oil!

# Minimum but finite dimensions are required for all reserves parameters, such as area, net pay, and hydrocarbon recovery factor. The concept here is that a small but finite volume of oil or [[natural gas]], and some minimum reservoir thickness and quality, must be present for an [[accumulation]] even to be ''detected'' by an operator. In other words, the lower limit of an ''accumulation'' thus defined is substantially larger than 1 bbl of oil!

# The four geological chance factors are defined so as to include the concept of the ''practical'' lower limit, that is, a modicum of [[porosity]], [[permeability]], and thickness of reservoir rock; a closure sufficient to contain an accumulation large enough to sustain a production test (or even a prudent drill stem test); and a hydrocarbon charge and sealing capability sufficient for at least 50% hydrogen saturation.

# The four geological chance factors are defined so as to include the concept of the ''practical'' lower limit, that is, a modicum of [[porosity]], [[permeability]], and thickness of reservoir rock; a closure sufficient to contain an accumulation large enough to sustain a production test (or even a prudent drill stem test); and a hydrocarbon charge and sealing capability sufficient for at least 50% hydrogen saturation.

==Probability of commercial success==

==Probability of commercial success==

For exploration ventures, the recommended method to assess the chance of commercial success is to first identify the minimum field size associated with your firm's definition of the threshold of commerciality, and then to determine what proportion of such fields occur in the natural population of counterpart accumulations in the subject trend, play, or basin. This requires the geologist or engineer to construct a field size distribution, as previously discussed.

For exploration ventures, the recommended method to assess the chance of commercial success is to first identify the minimum field size associated with your firm's definition of the threshold of commerciality, and then to determine what proportion of such fields occur in the natural population of counterpart [[accumulation]]s in the subject trend, play, or basin. This requires the geologist or engineer to construct a field size distribution, as previously discussed.

===Example===

===Example===

==Applications to development projects==

==Applications to development projects==

In development projects, just as in exploration projects, the geological chance factors must be derived from the study of maps, cross sections, and well data. They cannot be "pulled out of the air." However, there is an important difference: the fact that development is contemplated at all implies that a petroleum accumulation exists, so the hydrocarbon charge and seal/trap requirements have generally been satisfied. The only remaining geological risks have to do with (1) structural variations that may depress the reservoir below the [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact oil-water contact] and (2) stratigraphic variations affecting both thickness and quality of the reservoir section.

In development projects, just as in exploration projects, the geological chance factors must be derived from the study of maps, cross sections, and well data. They cannot be "pulled out of the air." However, there is an important difference: the fact that development is contemplated at all implies that a petroleum [[accumulation]] exists, so the hydrocarbon charge and seal/trap requirements have generally been satisfied. The only remaining geological risks have to do with (1) structural variations that may depress the reservoir below the [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact oil-water contact] and (2) stratigraphic variations affecting both thickness and quality of the reservoir section.

Although individual development wells have a high probability of success, some development dry holes are drilled. Naturally, the proportion of development dry holes will vary according to the geological characteristics of individual fields and trends. Nevertheless, this failure rate is significant and must be anticipated in

Although individual development wells have a high probability of success, some development dry holes are drilled. Naturally, the proportion of development dry holes will vary according to the geological characteristics of individual fields and trends. Nevertheless, this failure rate is significant and must be anticipated in