Secondary Recovery

In primary natural resource recovery, the initial approach to produce oil, natural reservoir pressure or simple mechanical pumps are used to raise oil to the surface.  Most oil wells today have to be pumped.

Further oil production can be obtained by injecting water, 'waterflooding', to maintain reservoir pressure and push oil out of the rock. Prolonged oil production can be achieved effectively once the primary production has tapered off.  This is called secondary recovery.

Primary oil recovery can only produce a small fraction of the oil in a reservoir.  The need for secondary oil recovery methods arise from this fact.  Waterflooding can be both effective and economical and a well planned oil field can even diminish these costs.

By forcing water into the crevices around an oil reserve, oil can be 'moved' toward the production zone. Work is underway to improve the technology for use with heavy, more viscous crudes, once thought to be impractical.  The addition of a base, a soap like substance, can help free oil reserves currently attached to reservoir rock. This method can recover an additional 10 to 20 percent of the reservoirs original oil. Another method involves increasing the viscosity of the water, allowing for drillers to gain 'control' over where the water flows.  This allows for the introduction of water into areas of the reservoir in which it naturally wouldn't flow.

A well planed oil field can go a long way toward the reliability and overall cost effectiveness of a waterflooding project. One method uses centrally located  wells that, once primary and secondary production declines, will be used as injection wells. These injection wells use water to force the remaining oil reserves toward the extremities of the oil field.  Such techniques can raise production on these outer wells to near initial production numbers as well as allow for the recovery of up to 80% of the remaining reserves.

Oil reservoirs suitable for secondary recovery projects have been produced for several years. It takes time to inject sufficient water to fill enough of the void spaces to begin to move very much oil. In the months after the start of a waterflood, significant production increases take place and the flood will probably have maximum recoveries during the second, third, fourth, and fifth years after injection of water has commenced. The average waterflood usually lasts 6 to 10 years.

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