Oil and Natural Gas - Energy Policy Analysis: A Conceptual Framework - page 82

panies over a period of time. Frequently companies do not share their information and seismic
methodology is constantly being upgraded to find deeper, smaller, and more subtle targets. There
appears to be no consensus about which methods are the best (MDFWP 1983).
Drilling
If preliminary exploration reveals favorable results, exploratory drilling may take place. When
an area's fossil fuel potential is unknown, the drilling operation is called a “wildcat.” Prior to
drilling, a drill pad (well site) is cleared and leveled for the drill rig and associated equipment
and structures. Only by drilling a “wildcat well” (i.e., a well drilled in unproven territory) will a
company know if subsurface strata contain oil or gas and if its quality and quantity are adequate
for profitable sale.
The depth of wildcat wells and their rig size depend on the geology of an area. Wells drilled
to a depth of 10,000 to 15,000 feet are not uncommon. For deep wells, as much as five acres may
be needed to establish a drill pad, the drill rig, mud pit, tool shack, pipe rack, and generators.
Drilling equipment may remain on-site for six months. In other areas, shallower wells up to a few
thousand feet are common and may be completed in a few weeks (USDOI 1981a). Stratigraphic
tests involve drilling relatively shallow holes (100 to several thousand feet deep) to supplement
seismic data. These holes are usually drilled by truck-mounted rotary rigs that are fairly mobile;
consequently, roads and trails to test sites on level, solid ground are temporary and may involve
minimal construction. From 50,000 to 100,000 gallons of water a day may be needed for mixing
drilling mud, cleaning equipment, and cooling engines (USDOI 1981b). A surface pipeline may
be laid to a stream or a water well, or water may be trucked to the site. Once drilling is started, it
continues twenty-four hours a day until completion.
Drilling activities can have detrimental impacts on surface and ground waters, resulting in
harm to aquatic organisms, vegetation, and humans. Exploration drill holes may penetrate several
aquifers and result in leakage between aquifers and to the surface with possible degradation of
water quality (USDOI 1981b). Lowering the groundwater level in an aquifer can result in in-
creased pumping costs at nearby wells or can cause wells to go dry. Open holes present a danger
to domestic and wild animals, as well as humans. Improperly plugged drill holes allow surface
water to enter an aquifer. This may be detrimental to groundwater, depending on the quality and
degree of contamination of surface water. Other impacts from exploration drilling include noise,
damage to archeological and historical sites, and possible contamination by drilling muds and
fluids (USDOI 1981b).
Production Facilities
If wildcatting produces commercial quantities of hydrocarbons, a development phase is initi-
ated. Additional wells are drilled to establish the extent of a field. Field size may vary from less
than 1,000 acres to several thousand acres, and some cover several townships. Generally a state
agency governs the spacing of oil and gas wells. Often oil wells less than about 6,000 feet deep
are placed one per 40 acres; wells 6,000 to 11,000 feet, one per 160 acres; wells greater than
11,000 feet deep are one per 320 acres. Gas wells are often located one well per 640 acres. If an
oil field is developed on the minimum spacing pattern of forty acres per well and if the field is a
section (640 acres) in size, at least four miles of roads will be needed (USFS 1979). In addition
to roads, other surface uses needed for development are more well drill sites, on-site processing
facilities, and storage tanks.