Overview
	Geophysical Surveys
	Geological Surveys
	Maps of Surveys in the Gulf of Mexico
	G&G Publications

Geophysical Surveys

Geological surveying on the OCS consists of bottom sampling, shallow coring, and deep stratigraphic tests. These data are useful in determining the general geology of an area and whether the right types of rocks exist for petroleum formation and accumulation.

Bottom samples are obtained by dropping a weighted tube to the ocean floor and recovering it with an attached wire line. Depending upon the nature of the ocean floor, penetration is normally limited to a few tens of feet. Bottom samples can also be obtained from dredging.

Shallow coring is performed by conventional rotary drilling equipment to obtain a near-surface sample of the rocks of the seabed. Choice of location is carefully controlled to avoid any shallow (geological and manmade) hazards, for example, faults or environmentally sensitive areas. Penetration is limited to 50 feet of consolidated rock.

In any planning area, deep stratigraphic test wells, commonly known as continental offshore stratigraphic test (COST) wells, can be drilled to determine the geological character of rock strata. The location of such wells is carefully controlled by a permit issued by the MMS. These tests, which may be more than 20,000 feet deep, provide information that can be used by the Government and industry to evaluate tracts to be offered in a lease sale. Basically, an operator sets up a consortium of other companies where drilling costs are shared. The wells are drilled in accordance with MMS regulations. All stratigraphic tests must be completed 60 days before the sale and the information is released to the public 10 years after completion of the well or 60 calendar days after the issuance of the first oil and gas lease within 50 miles (80.6 km) of the well site. The last COST well was drilled in 1989, in the Central Gulf of Mexico. A discussion of the cost well program is described by Dellagiarino (1991).

The Resource Evaluation specialists at MMS have been using workstations with modern 3-D seismic and geological  interpretation software to:

	Determine the hydrocarbon potential of each of the OCS blocks
	Determine fair market value for the OCS tracts being offered for lease
	Determine fair market value for the OCS tracts being offered for lease;
	Assess undiscovered amounts of natural gas and oil;
	Quantify reserves of natural gas and oil on the OCS; and
	Perform post lease comparative analyses of company submitted bids for acceptance or rejection.

It has been of interest to compare the data acquisition statistics for the oil industry with those of MMS.

Industry has tended to acquire more data than the MMS. However, of the data shot by industry in the Alaska OCS, the MMS has acquired approximately 90 percent. Alaska remains a large frontier area with limited data coverage by industry, a fact that necessitates the MMS to acquire as much of these data as feasible. In recent years, the Gulf of Mexico has acquired most 3-D surveys and most large 2-D surveys. However, the MMS does not acquire the volume that industry obtains to reprocess.

The MMS acquired more data in the Atlantic Region than industry in 1976 and 1983. Before 1976, the MMS database was limited because industry had shown very little interest in leasing this frontier area, although industry had been acquiring geophysical data.

During the period 1976 to 1984, the MMS not only acquired most of the industry data, but purchased much of the pre-1976 data. Since 1985, there has been less activity, reflecting a decrease in industry interest.

Some of the reasons the MMS does not acquire all the data held by industry are as follows:

	Redundancy of data, because industry does not share it,
	Difference in data quality,
	Budgetary constraints,
	Personnel limitations for data reduction and interpretations, and
	Data storage, retrieval and display limitations.

In conclusion, totals for mileage acquired, permits issued, and expenditures reflect the overall trends of oil and gas pricing, limitations of areas due to offshore moratoria, and a shift of industry emphasis to foreign theatres.