70 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
3.2 Drilling
Drilling is the final stage of the exploratory program and is in fact
the only method by which a petroleum reservoir can be conclusively
identified. However, in keeping with the concept of site specificity,
drilling may be the only option in some areas for commencement of
the exploration program. The risk involved in the drilling operation
depends upon previous knowledge of the site subsurface. Thus,
there is the need to relate the character of the exploratory wells at a
given site to the characteristics of the reservoir.
Generally the first stage in the extraction of crude oil is to drill a
well into the underground reservoir. Often many wells called multilateral wells will be drilled into the same reservoir, to ensure that
the extraction rate will be economically viable. Also, some wells
known as secondary wells may be used to pump water, steam,
acids, or various gas mixtures into the reservoir to raise or maintain
the reservoir pressure, and so maintain an economic extraction rate.
Drilling for oil is a complex operation and has evolved considerably over the past 100 years. The older cable tool method, used
almost extensively until 1900, involves raising and dropping a
heavy bit and drill stem attached by cable to a cantilever arm at
the surface. It pulverizes the rock and earth, gradually forming
the hole. The cable tool system is generally preferred only for penetrating hard rock at shallow depths and when oil reservoirs are
expected at the shallow depths. The weight of the column is usually
enough to attain penetration but can be augmented by a hydraulic
pressure cylinder at the surface.
3.2.1 Preparing to Drill
Once the site has been selected, it must be surveyed to determine
its boundaries, and environmental impact studies may need to be
performed. Lease agreements, titles, and right of way accesses for
the land must be obtained and evaluated legally. For offshore sites,
legal jurisdiction must be determined and drilling can only commence when these issues have been settled.
Once the land has been prepared, several holes must be dug to
make way for the rig and the main hole. A rectangular pit, or cellar, is dug around the location of the actual drilling hole. The cellar
provides a workspace around the hole, for the workers and drilling
accessories. The crew then begins drilling the main hole, often with
a small drill truck rather than the main rig. The first part of the hole
3.2 Drilling
Drilling is the final stage of the exploratory program and is in fact
the only method by which a petroleum reservoir can be conclusively
identified. However, in keeping with the concept of site specificity,
drilling may be the only option in some areas for commencement of
the exploration program. The risk involved in the drilling operation
depends upon previous knowledge of the site subsurface. Thus,
there is the need to relate the character of the exploratory wells at a
given site to the characteristics of the reservoir.
Generally the first stage in the extraction of crude oil is to drill a
well into the underground reservoir. Often many wells called multilateral wells will be drilled into the same reservoir, to ensure that
the extraction rate will be economically viable. Also, some wells
known as secondary wells may be used to pump water, steam,
acids, or various gas mixtures into the reservoir to raise or maintain
the reservoir pressure, and so maintain an economic extraction rate.
Drilling for oil is a complex operation and has evolved considerably over the past 100 years. The older cable tool method, used
almost extensively until 1900, involves raising and dropping a
heavy bit and drill stem attached by cable to a cantilever arm at
the surface. It pulverizes the rock and earth, gradually forming
the hole. The cable tool system is generally preferred only for penetrating hard rock at shallow depths and when oil reservoirs are
expected at the shallow depths. The weight of the column is usually
enough to attain penetration but can be augmented by a hydraulic
pressure cylinder at the surface.
3.2.1 Preparing to Drill
Once the site has been selected, it must be surveyed to determine
its boundaries, and environmental impact studies may need to be
performed. Lease agreements, titles, and right of way accesses for
the land must be obtained and evaluated legally. For offshore sites,
legal jurisdiction must be determined and drilling can only commence when these issues have been settled.
Once the land has been prepared, several holes must be dug to
make way for the rig and the main hole. A rectangular pit, or cellar, is dug around the location of the actual drilling hole. The cellar
provides a workspace around the hole, for the workers and drilling
accessories. The crew then begins drilling the main hole, often with
a small drill truck rather than the main rig. The first part of the hole