Undiscovered Oil and Gas Resources An Evaluation of the Department of the Interior's 1989 Assessment Procedures (1991) / Chapter Skim
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B Adequacy of the Data Base for Hydrocarbon Estimates of the Georges Bank Area of the North Atlantic Outer Continental Shelf
B Adequacy of the Data Base for Hydrocarbon Estimates of the Georges Bank Area of the North Atlantic Outer Continental Shelf
Pages 125-158
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From page 125... ...
AppendLx B Adequacy of the Data Base for Hydrocarbon Estimates of the Georges Bank Area of the North Atlantic Outer Continental Shelf Committee on Undiscovered Oil and Gas Resources Board on Earth Sciences and Resources Commission on Physical Sciences, Mathematics, and Resources National Research Council National Academy Press Washington, D.C.
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From page 126... ...
. Because of its particular expertise, this group, the Committee on Undiscovered Oil and Gas Resources, was assigned the subtask of evaluating the data base for the estimates of hydrocarbon resources in the Georges Bank basin made by MMS in conjunction
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From page 127... ...
Because the MMS uses the same statistical methodology and applies the same economic considerations for its regional resource evaluation as it did for the national assessment, the panel of the full committee that reviewed the Georges Bank data base was unable to address the issue of the quantitative statistical methodology in its report. Besides reviewing the data base according to the charge to the committee, however, the report also addresses aspects of the MMS's approach to assessing the resource potential of the Georges Bank basin, such as how the MMS used the geological, geophysical, and geochemical data base, the validity of the MMS's extrapolations to areas lacking data, the MMS's practice of basing estimates of critical parameters on single numbers (point estimates)
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From page 128... ...
This report on the adequacy of the data base used by the MMS to estimate the hydrocarbon potential of the Georges Bank basin and on the credibility of that estimate is based mainly on the panel's meeting with the MMS's North Atlantic Region office staff, but it also draws on information and deliberations relating to the national assessment, because the MMS's methods and procedures have been essentially the same for both activities. The Committee on Undiscovered Oil and Gas Resources expresses its appreciation to the MMS and its officials, whose cooperation and organized efforts resulted in a productive and informative meeting that led to the observations and evaluations described in this report.
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From page 131... ...
wells and eight unsuccessful industry exploratory wells have provided a large amount of stratigraphic, geochemical, and geophysical data, those data do not necessarily hold for the other four play types. The MMS has a vast amount of seismic reflection data ranging in quality from poor to excellent and covering a wide area of the Georges Bank portion of the OCS.
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From page 132... ...
Also, because it is highly unlikely that all the prospects have been identified in any play type in this frontier province, the fact that the MMS's estimate of the total prospects is approximately equal to the number of identified prospects indicates that the MMS has underestimated severely the true number of prospects in the basin. The lack of success in the one explored area of the Georges Bank basin appears to have led to low estimates of potential resources for the rest of the area.
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From page 133... ...
steps to ensure careful reconsideration of the resource estimation. To enhance the data base and to reduce uncertainty in the estimates of oil and gas resources in the Georges Bank basin, the panel recommends the following: 1.
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From page 134... ...
5. Reevaluate the lower limit for the range of acreage assigned to each The Committee on Undiscovered Oil and Gas Resources concurred with the panel's findings and in its forthcoming report will elaborate further on the MMS's resource estimation methodologies and procedures, which, in the committee's judgment, tend to produce overly conservative estimates of undiscovered oil and gas resources.
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From page 135... ...
Geological Survey (USGS) in their most recent joint national assessment of undiscovered conventional oil and gas resources of the United States (U.S.
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From page 136... ...
and establishing exploration plays2 were examined and typical prospects within exploration plays were reviewed. After reviewing information relating to the factors that cause hydrocarbon accumulations, the panel examined the procedures by which the potential resources of the basin were determined and made a judgment as to the adequacy of the assessment of undiscovered oil and gas resources assigned by the MMS to the Georges Bank basin.
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From page 137... ...
Geologic History The Georges Bank area provides evidence for a generally accepted geologic history that includes the entire North Atlantic region. Older sedimentary strata, accumulated prior to the rifting and separation of a large continental mass into the present-day continents, lie below younger marine and terrigenous deposits formed in the Triassic and Jurassic Periods during and after continental rifting.
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From page 138... ...
SOURCE: Minerals Management Service, Atlantic Region.
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From page 139... ...
Therefore, Cretaceous and Tertiary sedimentary strata are nearly all sandstones, shales, and siltstones with some thin, interbedded limestones. A pronounced shelf edge was established by the middle of Late Jurassic time as the ocean basin continued to subside (Fig.
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From page 141... ...
The seismic grid, ranging from 1/8 mile by 1/8 mile in the lease sale areas to 3 miles by 3 miles outside, as well as other geophysical parameters, were chosen by the industry using standard, state-of-the-art geophysical practice adequate for locating potential oil-bearing structures. The seismic grid for the Georges Bank basin is spaced sufficiently to identify significant structures that may contain hydrocarbons, but the processing of some lines may not be adequate to identify all of the existing structures in a particular play.
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From page 142... ...
High concentration of seismic lines in vicinity of 41°N latitude/68°W longitude is location of two COST wells and several industry exploratory wells. SOURCE: Minerals Management Service, Atlantic Region.
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From page 143... ...
The seismic data were integrated with the available geologic data taken from a small number of wells in an effort to relate seismic reflection events to specific geologic horizons. Only ten wells have been drilled in a limited area of the basin (see Fig.
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From page 144... ...
it must be noted that the use of geophysical data alone for estimating oil and gas resources has limitations. Any procedure that relies solely on such information is beset by uncertainties that affect estimates of the undiscovered oil and gas resources estimates of the area.
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From page 145... ...
Upper Jurassic and Lower Cretaceous sedimentary wedgeouts against the slope and seaward edge of the reef trend, and (5) structural traps seaward of the continental shelf in Upper Jurassic and Lower Cretaceous strata.
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From page 146... ...
The MMS has defined the geological parameters that could produce hydrocarbon accumulations in this frontier province. As with any frontier province lacking established production, the initial efforts to locate hydrocarbon accumulations have been focused on the most obvious structural traps, which has resulted in the less obvious stratigraphic and combination-type traps initially remaining unrecognized.
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From page 147... ...
This deficiency is particularly relevant to the resource assessment, because prospects seaward of the reef edge are likely to exhibit an organic content much higher than that observed on the shelf and should become more sapropellic. The oil- and gas-generating potential seaward of the reef edge, and consequently the probable hydrocarbon resources, should be greater than the resources on the shelf because of the presence of more favorable organic source material (Bayliss, 1985, Figs.
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From page 148... ...
As the source rocks associated with the carbonates of the area are more oil-prone than are the deeper elastic rocks, the carbonate reef trend should have a greater potential for liquids than for gas.
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From page 149... ...
Approximately 79 percent of the risked4, economically recoverable resources reported by the MMS are assigned to two play types: anticlines on the continental shelf and structures within Triassic rift basins. The former play type 4 Risk is the probability that no commercial oil or gas field exists.
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From page 150... ...
and structural traps seaward of the continental shelf may not be given proper consideration. Only 21 percent of the hydrocarbon resources in the Georges Bank basin are expected to come from the five other play types.
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From page 151... ...
The panel considers the range of acreage assigned to prospects to be too wide. For example, the acreage assigned for the shelf anticline play ranges from 6 to 36,780 acres for 90 prospects; the area assigned for the anticline play seaward of the reef trend ranges from 18 to 12,590 acres; the Triassic rift basin play is assigned a range from 2 to 16,583 acres.
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From page 152... ...
the combined effects several practices in r ~ MMS's approach to resource estimation result in very conservative estimates of the potential oil and gas resources in the Georges Bank basin of the North Atlantic OCS.
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From page 153... ...
The estimates produced by the MMS for oil and gas resources in the Georges Bank basin are judged by the panel to be overly conservative because of the following MMS practices in its resource assessments: 1. Using single-number estimates instead of ranges of key quantities; Assuming that the total number of prospects in a play is equal to the number of identified prospects; 3.
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From page 154... ...
B-30 APPENDIX B Ignoring the potential of stratigraphic traps in favor of the more obvious structural traps; and 6. Inadequately incorporating expressions of uncertainty in the estimation process, a necessary step given the lack of drill information for four of the five play types in the basin.
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From page 155... ...
steps to ensure careful reconsideration of the resource estimation. Data Needs With additional investigative resources, much needed information essential to a credible estimate of the hydrocarbon resources could be obtained that would reduce the uncertainty and lead to more realistic estimates.
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From page 156... ...
2. Obtain reprocessed seismic data for portions of the carbonate reef trend to evaluate more fully the reservoir characteristics of these strata.
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From page 157... ...
APPENDIX B =-~o ~ ~0 Two, fir ~ and About John ad, edit 1980. Ceo~c and O~mbonal Summary COW Ad.
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