Table IV-13. The Proposed Action (Alternative-1) - Exploration and Development Scenario

'Gulf of Mexico Region - shore facilities; 1 Gas processing plant, 4 oil pipeline shore facilities and 1 waste disposal facility.

'Gulf of Mexico Region - shore facilities; 4 oil pipeline shore facilities and 3 waste disposal facilities.

various factors are considered when developing the exploration and development infrastructure: geology of the area, costs associated with exploration and development, the presence of existing infrastructure to transport oil or gas to market, and environmental conditions in the area. Because these factors vary from region to region, the infrastructure required to find and develop similar volumes of hydrocarbons differs among the regions. For example, the number of wells assumed for the scenarios in the Western and Central Gulf of Mexico Planning Areas is greater than in other regions. The western and central Gulf are mature areas with proven prospects and multiple traps for hydrocarbons. Numerous wells would be needed to explore, delineate, and develop these prospects. On the other hand, in frontier areas such as the Alaska Region, only the largest prospects can be explored because of the high costs involved and the unproven geologic potential of the area. Therefore, significantly fewer exploration wells would be drilled.

These same conditions also influence the number of development wells required. Because of several factors in the Gulf of Mexico, especially the existing infrastructure, many relatively small prospects can be developed in the region. Additional scenario elements specific to the Gulf of Mexico region can be found in table IV-13a. Similar size prospects in the Alaska Region could not be developed at this time because of higher costs and the lack of existing infrastructure. Therefore, more development wells are assumed for the scenarios in the western and central Gulf than in Alaska and other regions.

Estimates of the level of offshore and onshore activities which may result from the exploration, the delineation of possible hydrocarbon bearing formations, and the establishment of production platforms are also based on the following assumptions:

The areas under consideration for lease are assumed to be leased and developed.

The amount of oil and natural gas assumed to be discovered, developed, and produced is based on the condition that economically recoverable amount of hydrocarbons are present in the planning areas.

The level of infrastructure for each area under consideration for lease is based on the assumption that all of the conditional resources allocated to each sale will be produced independent of the likelihood of finding hydrocarbons.

TRANSPORTATION and MARKET ASSUMPTIONS: The exact mode of transport of oil and gas cannot be determined until the amount of recoverable reserves is known and judgments are made as to what is environmentally preferable and technically and economically feasible. Therefore, the assumptions listed below were made concerning how oil and gas production will be transported to shore and whether production will be transported by tanker or pipeline to markets inside or outside of the areas being considered for lease. Assumptions for all the planning areas are provided. However, only eight planning areas are being considered for lease sales in the proposed program. These assumptions are limited to the transport of crude oil and gas to existing infrastructure and among domestic market areas. In developing these assumptions, the current and proposed transportation networks to demand areas were reviewed.

Assumptions whether to use pipelines, barges, or tankers to transport OCS oil and gas to shore take into consideration technological and environmental constraints and economic considerations. Although pipelines were generally preferred, in some instances where economics and other considerations did not justify their construction, tankers or barges were assumed.

Gulf of Mexico Region:

Approximately 90 percent of the oil from the Western and Central Gulf of Mexico Planning Areas would be transported to shore by the extension and expansion of the existing offshore pipeline system.

Less than 1 percent of the oil from the Western and Central Gulf of Mexico Planning Areas in nearshore areas would be transported by barge; approximately 10 percent of the oil produced in deepwater would be transported to shore by shuttle tanker.

Gas from the Western and Central Gulf of Mexico Planning Areas would be transported to shore by pipeline through the extension and expansion of the existing pipeline system. Gas from the Eastern Gulf of Mexico would be transported to shore by pipeline to the Central Gulf of Mexico Planning Area.

One hundred percent of the oil from the Eastern Gulf of Mexico Planning Area would be transported by pipeline to existing facilities in the Central Gulf of Mexico Planning Area.

New onshore facilities would include marine terminals and pipeline yards.

Alaska Region:

Oil from the Beaufort and Chukchi Sea Planning Areas would be transported by new subsea and overland pipelines to the Trans-Alaska Pipeline System (TAPS). TAPS would carry the oil south to the marine terminal facilities in Valdez where it would be loaded on tankers and shipped to West Coast.

Oil from the Hope Basin Planning Area would be transported by tanker from an offshore production/loading platform to West Coast ports.

Oil from the Cook Inlet Planning Area would be transported from production platforms to onshore facilities in Nikiski using new subsea and overland pipelines. Refined oil products would largely be utilized in Alaska markets.

Oil from the Gulf of Alaska Planning Area could either be transported by new subsea pipeline to onshore facilities in the Yakutat area from which it would be shipped by tankers to West Coast ports; or, it could be loaded on tankers from floating production/storage platforms for shipment to West Coast ports.

Natural gas will not be economic to develop and produce in the Alaska Region with the possible exception of Cook Inlet. Present natural gas supplies are adequate for the local market in southcentral Alaska. If natural gas is produced in Cook Inlet, it would be transported to shore by pipeline. An analysis of the types of impacts that could occur if natural gas is discovered and produced in the Alaska Region is presented in section IV.A.2. and in the final EIS for proposed Cook Inlet Lease Sale 149 (USDOI, MMS, 1996).

New onshore facilities would include tank farms, docks, air bases, utilities, supply depots, and personnel quarters.

Pacific Region:

Alaska OCS oil transported by tanker to West Coast ports would be handled by existing onshore facilities.

Some of the large spills from Alaska OCS tankers could occur along the U.S. West Coast, offshore Mexico, or in the Gulf of Mexico.

OIL-SPILL ASSUMPTIONS:

Oil Spills Greater Than or Equal to 1,000 BBL. To provide a framework for the impact analysis of oil spills, assumptions are made concerning the likelihood of oil spills of 1,000 bbl or greater occurring. Since the accidental discharge of oil can occur during almost any stage of exploration, development, or production, MMS uses spill rates based on historical accidents to estimate the mean number of spills assumed to occur.

Several revisions of the spill rates have been made (Lanfear and Amstutz, 1983; Anderson and LaBelle, 1990; and Anderson and LaBelle, 1994). Oil spills of 1,000 bbl or greater (and 10,000 bbl or greater) from platforms and pipelines were most recently analyzed in Anderson and Labelle (1994). These platform and pipeline spill rates were derived from U.S. OCS spill data from 1964 to 1992. Anderson and LaBelle (1994) introduced spill rates for crude oil spills from tankers in U.S. waters derived from U.S. coastal and offshore tanker spill data from 1974 to 1992. In the same article, spill rates were introduced for spills from tankers transporting North Slope crude from Valdez to the U.S. west coast (and points beyond) based on data from

1977 (when the TAPS began operation) through 1992. Also introduced were spill rates for crude oil spills from barges in U.S. coastal, offshore, and inland waters based on U.S. data from 1974 to 1992.

Table IV-14 presents the number of oil spills estimated to occur as a result of the production and transportation of oil from the planning area. The source and number of assumed spills were based on the volume of anticipated oil production listed in table IV-13, on the assumed mode of transportation (pipeline and/or tanker), and on the spill rates for spills 1,000 bbl or greater. It is also assumed that these spills would occur with uniform frequency over the life of the proposed action.

The probability of one or more spills occurring in a given production period was estimated using the mean number of spills in a Poisson distribution. Table IV-14 presents the probabilities of one or more spills of 1,000 bbl or greater and 10,000 bbl or greater. These probabilities are based on the total estimated mean number of spills assumed to occur as a result of oil production from the planning areas.

Assumptions regarding the location of spills are based on the source of the spill, the transportation and market assumptions, location of existing infrastructure, and the location of the resources being analyzed. Platform spills were assumed to occur in the area proposed for consideration for lease. Pipeline spills were assumed to occur between the proposed area for consideration for lease and the existing infrastructure. Tanker and barge spills were assumed to occur along the tanker and barge routes. Additional assumptions concerning oil spills may be stated by the analyst within the impact analysis of their resource.

Spills from tankers carrying oil produced in the Beaufort and Chukchi Sea Planning Areas are assumed to occur outside of those planning areas. Oil produced in the Beaufort and Chukchi Sea Planning Areas would be transported by the TAPS to the Valdez terminal facilities and then transported by tanker to west coast ports. Based on the destination and amount of the TAPS oil shipped from Valdez to west coast ports (Puget Sound, Washington, San Francisco, and Los Angeles, California), it is reasonable to assume that tanker spills could occur along the tanker routes to these ports.