EXPLORATION, RECOVERY, AND TRANSPORTATION 77
to the flow of fluids in reservoirs and lead to high residual oil saturation. Reservoirs containing crude oils with low API gravity often
cannot be produced efficiently without application of enhanced oil
recovery (EOR) methods because of the high viscosity of the crude
oil. In some cases, the reservoir pressure was depleted prematurely
by poor reservoir management practices to create reservoirs with
low energy and high oil saturation.
Recovery of oil when a well is first opened is usually by natural
flow forced by the pressure of the gas or fluids that are contained
within the deposit. There are several means that serve to drive
the petroleum fluids from the formation, through the well, and to
the surface, and these methods are classified as either natural or
applied flow.
3.3.1 Primary Recovery (Natural Methods)
If the underground pressure in the oil reservoir is sufficient, then
the oil will be forced to the surface under this pressure. Gaseous
fuels or natural gas are usually present, which also supplies needed
underground pressure. In this situation it is sufficient to place a
complex arrangement of valves (the Christmas tree) at the wellhead to connect the well to a pipeline network for storage and processing. This is called primary oil recovery.
Thus, primary oil production (primary oil recovery) is the first
method of producing oil from a well and depends upon natural reservoir energy to drive the oil through the complex pore network to
producing wells. If the pressure on the fluid in the reservoir is great
enough, the oil flows into the well and up to the surface. Such driving energy may be derived from liquid expansion and evolution of
dissolved gases from the oil as reservoir pressure is lowered during
production, expansion of free gas, or a gas cap, influx of natural
water, gravity, or combinations of these effects.
Crude oil moves out of the reservoir into the well by one or more
of three processes. These processes are: dissolved gas drive, gas
cap drive, and water drive. Early recognition of the type of drive
involved is essential to the efficient development of an oil field.
In dissolved gas drive, the propulsive force is the gas in solution in the oil, which tends to come out of solution because of the
pressure release at the point of penetration of a well. Dissolved gas
drive is the least efficient type of natural drive as it is difficult to
control the gas-oil ratio; the bottom-hole pressure drops rapidly,
to the flow of fluids in reservoirs and lead to high residual oil saturation. Reservoirs containing crude oils with low API gravity often
cannot be produced efficiently without application of enhanced oil
recovery (EOR) methods because of the high viscosity of the crude
oil. In some cases, the reservoir pressure was depleted prematurely
by poor reservoir management practices to create reservoirs with
low energy and high oil saturation.
Recovery of oil when a well is first opened is usually by natural
flow forced by the pressure of the gas or fluids that are contained
within the deposit. There are several means that serve to drive
the petroleum fluids from the formation, through the well, and to
the surface, and these methods are classified as either natural or
applied flow.
3.3.1 Primary Recovery (Natural Methods)
If the underground pressure in the oil reservoir is sufficient, then
the oil will be forced to the surface under this pressure. Gaseous
fuels or natural gas are usually present, which also supplies needed
underground pressure. In this situation it is sufficient to place a
complex arrangement of valves (the Christmas tree) at the wellhead to connect the well to a pipeline network for storage and processing. This is called primary oil recovery.
Thus, primary oil production (primary oil recovery) is the first
method of producing oil from a well and depends upon natural reservoir energy to drive the oil through the complex pore network to
producing wells. If the pressure on the fluid in the reservoir is great
enough, the oil flows into the well and up to the surface. Such driving energy may be derived from liquid expansion and evolution of
dissolved gases from the oil as reservoir pressure is lowered during
production, expansion of free gas, or a gas cap, influx of natural
water, gravity, or combinations of these effects.
Crude oil moves out of the reservoir into the well by one or more
of three processes. These processes are: dissolved gas drive, gas
cap drive, and water drive. Early recognition of the type of drive
involved is essential to the efficient development of an oil field.
In dissolved gas drive, the propulsive force is the gas in solution in the oil, which tends to come out of solution because of the
pressure release at the point of penetration of a well. Dissolved gas
drive is the least efficient type of natural drive as it is difficult to
control the gas-oil ratio; the bottom-hole pressure drops rapidly,