The role of a production engineer

The role of a production engineer is to maximize oil and

gas production in a cost-effective manner. Familiarization

and understanding of oil and gas production systems are

essential to the engineers. This chapter provides graduat-ing production engineers with some basic knowledge

about production systems. More engineering principles

are discussed in the later chapters.

As shown in Fig. 1.1, a complete oil or gas production

system consists of a reservoir, well, flowline, separators,

pumps, and transportation pipelines. The reservoir sup-plies wellbore with crude oil or gas. The well provides a

path for the production fluid to flow from bottom hole to

surface and offers a means to control the fluid production

rate. The flowline leads the produced fluid to separators.

The separators remove gas and water from the crude oil.

Pumps and compressors are used to transport oil and gas

through pipelines to sales points.

1.2 Reservoir

Hydrocarbon accumulations in geological traps can be clas-sified as reservoir, field, and pool. A ‘‘reservoir’’ is a porous

and permeable underground formation containing an indi-vidual bank of hydrocarbons confined by impermeable rock

or water barriers and is characterized by a single natural

pressure system. A ‘‘field’’ is an area that consists of one or

more reservoirs all related to the same structural feature. A

‘‘pool’’ contains one or more reservoirs in isolated structures.

Depending on the initial reservoir condition in the phase

diagram (Fig. 1.2), hydrocarbon accumulations are classi-fied as oil, gas condensate, and gas reservoirs. An oil that

is at a pressure above its bubble-point pressure is called an

‘‘undersaturated oil’’ because it can dissolve more gas at

the given temperature. An oil that is at its bubble-point

pressure is called a ‘‘saturated oil’’ because it can dissolve

no more gas at the given temperature. Single (liquid)-phase

flow prevails in an undersaturated oil reservoir, whereas

two-phase (liquid oil and free gas) flow exists in a sat-urated oil reservoir.

Wells in the same reservoir can fall into categories of

oil, condensate, and gas wells depending on the producing

gas–oil ratio (GOR). Gas wells are wells with producing GOR

being greater than 100,000 scf/stb; condensate wells are those

with producing GOR being less than 100,000 scf/stb but

greater than 5,000 scf/stb; and wells with producing GOR

being less than 5,000 scf/stb are classified as oil wells.

Oil reservoirs can be classified on the basis of boundary

type, which determines driving mechanism, and which are

as follows:

.Water-drive reservoir

.Gas-cap drive reservoir

.Dissolved-gas drive reservoir

In water-drive reservoirs, the oil zone is connected by

a continuous path to the surface groundwater system (aqui-fer). The pressure caused by the ‘‘column’’ of water to the

surface forces the oil (and gas) to the top of the reservoir

against the impermeable barrier that restricts the oil and gas

(the trap boundary). This pressure will force the oil and gas

toward the wellbore. With the same oil production, reservoir

pressure will be maintained longer (relative to other mech-anisms of drive) when there is an active water drive. Edge-water drive reservoir is the most preferable type of reservoir

compared to bottom-water drive. The reservoir pressure can

remain at its initial value above bubble-point pressure so that

single-phase liquid flow exists in the reservoir for maximum

well productivity. A steady-state

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