Page 239 - Hydrocarbon Exploration and Production Second Edition

226 Enhanced Oil Recovery

cumulative oil production and the logarithm of the water cut. These assumptions
become more robust when based on a fit to measured production data.
The most reliable way of generating production profiles, and investigating the
sensitivity to well location, perforation interval, surface facilities constraints, etc., is
through reservoir simulation.
Finally, external constraints on the production profile may arise from

production ceilings (e.g. The Organization of the Petroleum Exporting Countries
(OPEC) production quotas)
host government requirements (e.g. generating long period of stable income)
customer demand (e.g. gas sales contract for 10 year stable delivery)
production licence duration (e.g. limited production period under a PSC).

9.8. Enhanced Oil Recovery

EOR techniques seek to produce oil which would not be recovered using the
primary or secondary recovery methods discussed so far. Three categories of EOR
exist

thermal techniques
chemical techniques
miscible processes.

Thermal techniques are used to reduce the viscosity of heavy crudes, thereby
improving the mobility, and allowing the oil to be displaced to the producers. This
is the most common of the EOR techniques, and the most widely used method of
heat generation is by injecting hot water or steam into the reservoir. This can be
done in dedicated injectors (hot water or steam drive), or by alternately injecting into,
and then producing from the same well (steam soak). A more ambitious method of
generating heat in the reservoir is by igniting a mixture of the hydrocarbon gases
and oxygen, and is called in-situ combustion.
Chemical techniques change the physical properties of either the displacing fluid,
or of the oil, and comprise of polymer flooding and surfactant flooding.
Polymer flooding aims at reducing the amount of by-passed oil by increasing
the viscosity of the displacing fluid, say water, and thereby improving the mobility
ratio (M ).
Recall that

k rw =m w
Mobility ratio ðMÞ¼
k ro =m o
This technique is suitable where the natural mobility ratio is greater than 1.0.
Polymer chemicals such as polysaccharides are added to the injection water.
Surfactant flooding is targeted at reducing the amount of residual oil left in the
pore space, by reducing the interfacial tension between oil and water and allowing
the oil droplets to break down into small enough droplets to be displaced through