Page 35 - Oil and Gas Production Handbook An Introduction to Oil and Gas Production

hydraulic pipes, electrical power, control and communication signals. A
control pod with inert gas and/or oil protection contains control electronics,
and operates most equipment via hydraulic switches. More complex subsea
solutions may contain subsea separation/stabilization and electrical
multiphase pumping. This may be necessary if reservoir pressure is low,
offset (distance to main facility) is long or there are flow assurance problems
so that the gas and liquids will not stably flow to the surface.

The product is piped back through pipelines and risers to the surface. The
main choke may be located topside.

3.5.2 Injection

Wells are also divided into production and injection wells. The former are for
production of oil and gas. Injection wells are drilled to inject gas or water into
the reservoir. The purpose of injection is to maintain overall and hydrostatic
reservoir pressure and force the oil toward the production wells. When
injected water reaches the production well, it is called 'injected water
breakthrough'. Special logging instruments, often based on radioactive
isotopes added to injection water, are used to detect breakthrough.

Injection wells are fundamentally the same as production wellheads The
difference being their direction of flow and therefore mounting of some
directional components such as the choke.

3.6 Artificial lift

Production wells are free flowing or lifted. A free flowing oil well has enough
downhole pressure to reach suitable wellhead production pressure and
maintain an acceptable well-flow. If the formation pressure is too low, and
water or gas injection cannot maintain pressure or are not suitable, the well
must be artificially lifted. For smaller wells, 0.7 MPa (100 PSI) wellhead
pressure with a standing column of liquid in the tubing is measured, by a
rule-of-thumb method, to allow the well to flow. Larger wells will be equipped
with artificial lift to increase production even at much higher pressures. Some
artificial lift methods are:

3.6.1 Rod pumps
Sucker rod pumps, also called donkey or beam pumps, are the most
common artificial-lift system used in land-based operations. A motor drives a
reciprocating beam, connected to a polished rod passing into the tubing via a

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