36 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
then migrated through adjacent rock layers until they were trapped
underground in porous rock formations, or reservoirs. Hydrocarbon
accumulations in a reservoir require that the reservoir rock has the
capacity of transmit fluids (permeability) and to store fluids (porosity) as well as an impermeable basement rock and an impermeable
cap rock to prevent their escape.
The arguments against the abiotic theory involve various biomarkers which have been found in all samples of all the oil and gas
accumulations found to date. The prevailing view among geologists and petroleum engineers is that this evidence provides irrefutable proof that the oil and gas accumulations found up to now have
a biologic origin.
The composition of the precursors has a major influence on the
composition of petroleum and the relative amounts of these precursors (dependent upon the local flora and fauna) that occurred in the
source material added another variable to the composition of the
produced oil. Hence, it is not surprising that petroleum composition can vary with the location and age of the field, in addition to
any variations that occur with the depth of the individual well. Two
adjacent wells are more than likely to produce petroleum with very
different characteristics.
2.2 Reservoirs
Reservoir location and structure plays an important role in crude
oil economics — some would even say the most important role.
A reservoir is any porous and permeable stratum that will store
crude oil and a very common reservoir rock is a porous or fractured
limestone (especially of the reef, bioherm type); several such reservoir structures are found throughout the earth. Most reservoir rocks
are sedimentary rocks, almost always the coarser grained of the sedimentary rocks: sand, sandstone, limestone, and dolomite. A less common reservoir is a fractured shale or even igneous or metamorphic
rock. It is only rarely that shale acts as a reservoir rock, and again
fractures and other relatively wide openings are believed to confer
the required reservoir properties on an otherwise unsuitable rock.
2.2.1 Reservoir Structure
Petroleum accumulations are usually found in structural highs
(an anticline), where reservoir rocks of suitable porosity and
then migrated through adjacent rock layers until they were trapped
underground in porous rock formations, or reservoirs. Hydrocarbon
accumulations in a reservoir require that the reservoir rock has the
capacity of transmit fluids (permeability) and to store fluids (porosity) as well as an impermeable basement rock and an impermeable
cap rock to prevent their escape.
The arguments against the abiotic theory involve various biomarkers which have been found in all samples of all the oil and gas
accumulations found to date. The prevailing view among geologists and petroleum engineers is that this evidence provides irrefutable proof that the oil and gas accumulations found up to now have
a biologic origin.
The composition of the precursors has a major influence on the
composition of petroleum and the relative amounts of these precursors (dependent upon the local flora and fauna) that occurred in the
source material added another variable to the composition of the
produced oil. Hence, it is not surprising that petroleum composition can vary with the location and age of the field, in addition to
any variations that occur with the depth of the individual well. Two
adjacent wells are more than likely to produce petroleum with very
different characteristics.
2.2 Reservoirs
Reservoir location and structure plays an important role in crude
oil economics — some would even say the most important role.
A reservoir is any porous and permeable stratum that will store
crude oil and a very common reservoir rock is a porous or fractured
limestone (especially of the reef, bioherm type); several such reservoir structures are found throughout the earth. Most reservoir rocks
are sedimentary rocks, almost always the coarser grained of the sedimentary rocks: sand, sandstone, limestone, and dolomite. A less common reservoir is a fractured shale or even igneous or metamorphic
rock. It is only rarely that shale acts as a reservoir rock, and again
fractures and other relatively wide openings are believed to confer
the required reservoir properties on an otherwise unsuitable rock.
2.2.1 Reservoir Structure
Petroleum accumulations are usually found in structural highs
(an anticline), where reservoir rocks of suitable porosity and