8
1 INTRODUCTION
sediments. Using this information, facies analysis can delineate the optimum stratigraphic and geographic extent of coal-bearing facies. Detailed environmental studies
can then be used to map the distribution of individual coal seams. Coal can form in various deltaic subenvironments, such as interdistributary bays, within, or on the crests of
channel sands, as well as regionally uniform beds. The coals that form in these various
subenvironments may be different both in composition and areal geometry.
Evaporite deposits are another sedimentary rock of great economic importance,
forming the basis for chemical industries in many parts of the world. The main evaporite minerals, by bulk, are gypsum (CaSO4"2H20) and halite (NaC1). Many other salts
are rarer but of equal or greater economic importance. These include carbonates, chlorides, and sulfates. The genesis of evaporite deposits has been extensively studied both
in nature and experimentally in the laboratory. The study of evaporites is important,
not just because of the economic value of the minerals, but because of the close relationship between evaporites and petroleum deposits (Melvin, 1991). It is appropriate
to turn now from the applications of sedimentology to the extraction of rock, to consider those uses where only the pore fluids are sought and removed.
Porosity and permeability are typically found in sediments, rather than in igneous and
metamorphic rocks. Thus hydrogeology is principally concerned with evaluating the
water resources of sedimentary aquifers (Ingebritsen and Sanford, 1998). The world
shortage of potable water may soon become more important than the quest for energy.
It has been argued that hydrogeology is "merely petroleum geology upside down." This
is a shallow statement, yet it contains much truth. Many sedimentary rocks are excellent aquifers and sedimentology and stratigraphy may be used to locate and exploit
these. Hydrogeology, like petroleum geology, is largely concerned with the quest for
porosity and permeability. It is necessary for an aquifer, like an oil reservoir, to have
both the pore space to contain fluid and the permeability to give it up. Whereas an oil
reservoir requires an impermeable cap rock to prevent the upward dissipation of oil and
gas, an aquifer requires an impermeable seal beneath to prevent the downward flow
of water. Despite these fundamental differences, there are many points in common between the search for water and for petroleum. Both use regional stratigraphic and structural analyses to determine the geometry and attitude of porous beds. Both can use
facies studies and environmental analysis to fulfill these objectives.
1.3.1 Petroleum
As mentioned earlier, the search for petroleum has been the major driving force behind
the rapid expansion in sedimentology during the last half century. Almost all commercial petroleum accumulations are found within sedimentary rocks. The majority of petroleum geoscientists believe, therefore, that petroleum originates in sedimentary rocks.
Many Russians, however, from Mendele'ev (1877) to Porfir'ev (1974) and Pushkarev
(1995), argue that petroleum comes out of the mantle, a view championed in the west
by Gold (1979, 1999). Petroleum geology is beyond the scope of this volume, but Chapter 7 provides an introduction before embarking such texts as Selley (1998) and Gluyas
and Swarbrick (1999). Hydrocarbons are complex organic compounds that are found
in nature within the pores and fractures of rocks. They consist primarily of hydrogen
and carbon compounds with variable amounts of nitrogen, oxygen, and sulfur, together
1 INTRODUCTION
sediments. Using this information, facies analysis can delineate the optimum stratigraphic and geographic extent of coal-bearing facies. Detailed environmental studies
can then be used to map the distribution of individual coal seams. Coal can form in various deltaic subenvironments, such as interdistributary bays, within, or on the crests of
channel sands, as well as regionally uniform beds. The coals that form in these various
subenvironments may be different both in composition and areal geometry.
Evaporite deposits are another sedimentary rock of great economic importance,
forming the basis for chemical industries in many parts of the world. The main evaporite minerals, by bulk, are gypsum (CaSO4"2H20) and halite (NaC1). Many other salts
are rarer but of equal or greater economic importance. These include carbonates, chlorides, and sulfates. The genesis of evaporite deposits has been extensively studied both
in nature and experimentally in the laboratory. The study of evaporites is important,
not just because of the economic value of the minerals, but because of the close relationship between evaporites and petroleum deposits (Melvin, 1991). It is appropriate
to turn now from the applications of sedimentology to the extraction of rock, to consider those uses where only the pore fluids are sought and removed.
Porosity and permeability are typically found in sediments, rather than in igneous and
metamorphic rocks. Thus hydrogeology is principally concerned with evaluating the
water resources of sedimentary aquifers (Ingebritsen and Sanford, 1998). The world
shortage of potable water may soon become more important than the quest for energy.
It has been argued that hydrogeology is "merely petroleum geology upside down." This
is a shallow statement, yet it contains much truth. Many sedimentary rocks are excellent aquifers and sedimentology and stratigraphy may be used to locate and exploit
these. Hydrogeology, like petroleum geology, is largely concerned with the quest for
porosity and permeability. It is necessary for an aquifer, like an oil reservoir, to have
both the pore space to contain fluid and the permeability to give it up. Whereas an oil
reservoir requires an impermeable cap rock to prevent the upward dissipation of oil and
gas, an aquifer requires an impermeable seal beneath to prevent the downward flow
of water. Despite these fundamental differences, there are many points in common between the search for water and for petroleum. Both use regional stratigraphic and structural analyses to determine the geometry and attitude of porous beds. Both can use
facies studies and environmental analysis to fulfill these objectives.
1.3.1 Petroleum
As mentioned earlier, the search for petroleum has been the major driving force behind
the rapid expansion in sedimentology during the last half century. Almost all commercial petroleum accumulations are found within sedimentary rocks. The majority of petroleum geoscientists believe, therefore, that petroleum originates in sedimentary rocks.
Many Russians, however, from Mendele'ev (1877) to Porfir'ev (1974) and Pushkarev
(1995), argue that petroleum comes out of the mantle, a view championed in the west
by Gold (1979, 1999). Petroleum geology is beyond the scope of this volume, but Chapter 7 provides an introduction before embarking such texts as Selley (1998) and Gluyas
and Swarbrick (1999). Hydrocarbons are complex organic compounds that are found
in nature within the pores and fractures of rocks. They consist primarily of hydrogen
and carbon compounds with variable amounts of nitrogen, oxygen, and sulfur, together