142
The Chemistry and Technology of Petroleum
removed as necessary to obtain a crude oil of suitable vapor pressure for transport yet retaining
most of the natural gasoline constituents.
By far the most abundant extraneous material is water. Many wells, especially during their
declining years, produce vast quantities of salt water, and disposing of it is both a serious and an
expensive problem. Furthermore, the brine may be corrosive, which necessitates frequent replacement of casing, pipe, and valves, or it may be saturated so that the salts tend to precipitate upon
reaching the surface. In either case the water produced with the oil is a source of continuing trouble.
Finally, if the reservoir rock is an incoherent sand or poorly cemented sandstone, large quantities of
sand are produced along with the oil and gas. On its way to the surface, the sand has been known to
scour its way completely through pipes and fittings.
It must also be remembered that in any field where primary production is followed by a secondary
or enhanced production method, there will be noticeable differences in properties between the fluids
produced (Thomas et al., 1983, 1987). The differences in elemental composition may not reflect these
differences to any great extent but more significant differences will be evident from an inspection
of the physical properties. One issue that arises from the physical property data is that such oils may
be outside the range of acceptability for refining techniques other than thermal options. In addition,
overloading of thermal process units will increase as the proportion of the heavy oil in the refinery
feedstock increases. Obviously there is a need for more and more refineries to accept larger proportions of heavy crude oils as the refinery feedstock and have the capability to process such materials.
In summary, the technologies applied to oil recovery involve different concepts, some of which
can cause changes to the oil during production.
Technologies such as alkaline flooding, microemulsion (micellar/emulsion) flooding, polymer
augmented water flooding, and carbon dioxide miscible/immiscible flooding do not require or cause
any change to the oil. The steaming technologies may cause some steam distillation that can augment the process when the steam distilled material moves with the steam front and acts as a solvent
for oil ahead of the steam front (Prats, 1986). Again, there is no change to the oil although there may
be favorable compositional changes to the oil insofar as lighter fractions are recovered and heavier
materials remain in the reservoir (Richardson et al., 1992).
The technology where changes do occur involves combustion of the oil in situ. The concept of
any combustion technology requires that the oil be partially combusted and that thermal decomposition occur to other parts of the oil. This is sufficient to cause irreversible chemical and physical
changes to the oil to the extent that the product is markedly different to the oil in place. Recognition
of this phenomenon is essential before combustion technologies are applied to oil recovery.
Although this improvement in properties may not appear to be too drastic, nevertheless it usually is sufficient to have major advantages for refinery operators. Any incremental increase in the
units of hydrogen–carbon ratio can save amounts of costly hydrogen during upgrading. The same
principles are also operative for reductions in the nitrogen, sulfur, and oxygen contents. This latter
occurrence also improves catalyst life and activity as well as reduces the metals content.
In short, in situ recovery processes (although less efficient in terms of bitumen recovery relative
to mining operations) may have the added benefit of leaving some of the more obnoxious constituents (from the processing objective) in the ground.
6.7 TRANSPORTATION
Most oil fields are at a considerable distance from the refineries that convert crude oil into usable
products, and therefore the oil must be transported in pipelines and tankers (Figure 6.9). However,
most crude oil needs some form of treatment near the reservoir before it can be carried for considerable distances through the pipelines or in the tankers. Railroad cars and motor vehicles are also used
to a large extent for the transportation of petroleum products.
Fluids produced from a well are seldom pure crude oil. In fact, the oil often contains quantities
of gas, saltwater, or even sand. Separation must be achieved before transportation. Separation and
The Chemistry and Technology of Petroleum
removed as necessary to obtain a crude oil of suitable vapor pressure for transport yet retaining
most of the natural gasoline constituents.
By far the most abundant extraneous material is water. Many wells, especially during their
declining years, produce vast quantities of salt water, and disposing of it is both a serious and an
expensive problem. Furthermore, the brine may be corrosive, which necessitates frequent replacement of casing, pipe, and valves, or it may be saturated so that the salts tend to precipitate upon
reaching the surface. In either case the water produced with the oil is a source of continuing trouble.
Finally, if the reservoir rock is an incoherent sand or poorly cemented sandstone, large quantities of
sand are produced along with the oil and gas. On its way to the surface, the sand has been known to
scour its way completely through pipes and fittings.
It must also be remembered that in any field where primary production is followed by a secondary
or enhanced production method, there will be noticeable differences in properties between the fluids
produced (Thomas et al., 1983, 1987). The differences in elemental composition may not reflect these
differences to any great extent but more significant differences will be evident from an inspection
of the physical properties. One issue that arises from the physical property data is that such oils may
be outside the range of acceptability for refining techniques other than thermal options. In addition,
overloading of thermal process units will increase as the proportion of the heavy oil in the refinery
feedstock increases. Obviously there is a need for more and more refineries to accept larger proportions of heavy crude oils as the refinery feedstock and have the capability to process such materials.
In summary, the technologies applied to oil recovery involve different concepts, some of which
can cause changes to the oil during production.
Technologies such as alkaline flooding, microemulsion (micellar/emulsion) flooding, polymer
augmented water flooding, and carbon dioxide miscible/immiscible flooding do not require or cause
any change to the oil. The steaming technologies may cause some steam distillation that can augment the process when the steam distilled material moves with the steam front and acts as a solvent
for oil ahead of the steam front (Prats, 1986). Again, there is no change to the oil although there may
be favorable compositional changes to the oil insofar as lighter fractions are recovered and heavier
materials remain in the reservoir (Richardson et al., 1992).
The technology where changes do occur involves combustion of the oil in situ. The concept of
any combustion technology requires that the oil be partially combusted and that thermal decomposition occur to other parts of the oil. This is sufficient to cause irreversible chemical and physical
changes to the oil to the extent that the product is markedly different to the oil in place. Recognition
of this phenomenon is essential before combustion technologies are applied to oil recovery.
Although this improvement in properties may not appear to be too drastic, nevertheless it usually is sufficient to have major advantages for refinery operators. Any incremental increase in the
units of hydrogen–carbon ratio can save amounts of costly hydrogen during upgrading. The same
principles are also operative for reductions in the nitrogen, sulfur, and oxygen contents. This latter
occurrence also improves catalyst life and activity as well as reduces the metals content.
In short, in situ recovery processes (although less efficient in terms of bitumen recovery relative
to mining operations) may have the added benefit of leaving some of the more obnoxious constituents (from the processing objective) in the ground.
6.7 TRANSPORTATION
Most oil fields are at a considerable distance from the refineries that convert crude oil into usable
products, and therefore the oil must be transported in pipelines and tankers (Figure 6.9). However,
most crude oil needs some form of treatment near the reservoir before it can be carried for considerable distances through the pipelines or in the tankers. Railroad cars and motor vehicles are also used
to a large extent for the transportation of petroleum products.
Fluids produced from a well are seldom pure crude oil. In fact, the oil often contains quantities
of gas, saltwater, or even sand. Separation must be achieved before transportation. Separation and