22
Water for Energy and Fuel Production
over more porous sand or silt and the gradual compaction of these clays over years.
This compaction squeezes water and gas out of clay into more porous sand or silt.
The gas in the sand under so-called geopressure is usually found at the depth of
10,000–25,000 ft. Thus, it carries some similarity with “deep gas” [6,7,11]. A combination of high depth and high pressure makes the extraction of gas from such zones
very difficult. However, of all unconventional gas resources, geopressurized zones
hold the highest amount of gas reserve. Just like deep gas, geopressurized zones are
mostly found in the Gulf Coast region. It is estimated that the amount of natural gas
in the geopressurized zones can be anywhere between 5,000 and 49,000 Tcf. This
presents an incredible opportunity because at present the total technically recoverable gas resource is about 1100 Tcf (see the National Energy Technology Laboratory
[NETL] website for unconventional gas).
Gas in the geopressurized zones is usually dissolved in hot brine solution (about
150°C–200°C) under pressure. The high pressure makes gas recovery easy when
the gas is tapped from these zones. However, this gas is accompanied by water that
will have to be removed. The geopressurized zones contain three types of energy:
(1) the unconventional gas reserve, (2) the high-pressurized fluids that can impart
mechanical energy, and (3) the hot brine solution that may provide geothermal
energy. The recovery of these energy resources will require high investment costs
and large amount of water production, treatment, and usages [6,11,12] (see the
NETL website).
2.3 enhanCed Oil reCOVery (eOr) PrOCess
EOR is defined as the incremental ultimate oil that can be economically recovered
from a petroleum reservoir over oil that can be recovered from the same reservoir
by conventional primary and secondary methods. The intent of EOR is to increase
the effectiveness of oil removal from the pores of the rock (displacement efficiency)
and to increase the volume of the rock contacted by injected fluids (sweep efficiency)
[16,17]. The oil remaining after conventional recovery operations is retained in the
pore space of reservoir rock at a lower concentration than originally existed. This
residual oil is found as either droplets trapped in the individual pores or cluster of
pores or films partly coating the pore walls. Entrapment of this residual oil is predominantly due to capillary and surface forces as well as due to pore geometry.
Bypassing of oil in the reservoir occurs due to a number of reasons: (1) nonhomogeneity of the reservoir rock causing inefficient sweeping by the displacement
fluids; (2) simultaneous effects of viscous, gravity, and capillary forces; and (3) high
mobility of displacing fluid compared to that of oil. The net effect depends on the
conditions at individual locations. In general, gravity forces cause vertical segregation of the fluids and water tends to underrun the oil-containing rock [16,17].
The recovery of conventional oil from a reservoir requires pressure gradient to
push oil out from the reservoir to the surface. Initially, gas and water that accompany
oil provide this pressure, and because of that as indicated earlier, when oil comes out
of the ground, a significant amount of water (eight bbl of water per each bbl of oil)
accompanies it. Initially, this process may be facilitated by pumping the fluid out
of the ground by a pump. This is generally known as primary oil recovery process.
Water for Energy and Fuel Production
over more porous sand or silt and the gradual compaction of these clays over years.
This compaction squeezes water and gas out of clay into more porous sand or silt.
The gas in the sand under so-called geopressure is usually found at the depth of
10,000–25,000 ft. Thus, it carries some similarity with “deep gas” [6,7,11]. A combination of high depth and high pressure makes the extraction of gas from such zones
very difficult. However, of all unconventional gas resources, geopressurized zones
hold the highest amount of gas reserve. Just like deep gas, geopressurized zones are
mostly found in the Gulf Coast region. It is estimated that the amount of natural gas
in the geopressurized zones can be anywhere between 5,000 and 49,000 Tcf. This
presents an incredible opportunity because at present the total technically recoverable gas resource is about 1100 Tcf (see the National Energy Technology Laboratory
[NETL] website for unconventional gas).
Gas in the geopressurized zones is usually dissolved in hot brine solution (about
150°C–200°C) under pressure. The high pressure makes gas recovery easy when
the gas is tapped from these zones. However, this gas is accompanied by water that
will have to be removed. The geopressurized zones contain three types of energy:
(1) the unconventional gas reserve, (2) the high-pressurized fluids that can impart
mechanical energy, and (3) the hot brine solution that may provide geothermal
energy. The recovery of these energy resources will require high investment costs
and large amount of water production, treatment, and usages [6,11,12] (see the
NETL website).
2.3 enhanCed Oil reCOVery (eOr) PrOCess
EOR is defined as the incremental ultimate oil that can be economically recovered
from a petroleum reservoir over oil that can be recovered from the same reservoir
by conventional primary and secondary methods. The intent of EOR is to increase
the effectiveness of oil removal from the pores of the rock (displacement efficiency)
and to increase the volume of the rock contacted by injected fluids (sweep efficiency)
[16,17]. The oil remaining after conventional recovery operations is retained in the
pore space of reservoir rock at a lower concentration than originally existed. This
residual oil is found as either droplets trapped in the individual pores or cluster of
pores or films partly coating the pore walls. Entrapment of this residual oil is predominantly due to capillary and surface forces as well as due to pore geometry.
Bypassing of oil in the reservoir occurs due to a number of reasons: (1) nonhomogeneity of the reservoir rock causing inefficient sweeping by the displacement
fluids; (2) simultaneous effects of viscous, gravity, and capillary forces; and (3) high
mobility of displacing fluid compared to that of oil. The net effect depends on the
conditions at individual locations. In general, gravity forces cause vertical segregation of the fluids and water tends to underrun the oil-containing rock [16,17].
The recovery of conventional oil from a reservoir requires pressure gradient to
push oil out from the reservoir to the surface. Initially, gas and water that accompany
oil provide this pressure, and because of that as indicated earlier, when oil comes out
of the ground, a significant amount of water (eight bbl of water per each bbl of oil)
accompanies it. Initially, this process may be facilitated by pumping the fluid out
of the ground by a pump. This is generally known as primary oil recovery process.