Methods to Koop OH Deposits Producing

Within the past few years oilmen have been giving more thought to conservation. They realize that it is cheaper to keep in operation a well that is already producing than to allow that well to go dry and drill a new one.

One way to keep a field alive is by drilling "input" wells. The waste gas left after separation is forced back under pressure down into the oil sand through input wells. Here it builds up pressure and drives the oil which is still in the pores of the rock toward the well pipes. If there is not enough gas available, water, and sometimes compressed air, is used.

Wells occasionally become blocked by pieces of asphalt, wax, or other solid material. In this case, the obstruction can be dissolved by pumping water into the well. AnotherT technique is pumping water and sand into the well under high pressure.

Thermal/recovery technique includes the injection of heated water or steam in the reservoir. This process leads to reducing oil, viscosity and improving its flow characteristics.

In this way wells are kept flowing longer. All of these techniques have greatly increased the amount of oil that can be recovered. In the early days of the industry, as much as 75% (percent) of the oil had

Oil Recovery 97

exercise

been left in the ground. With more modern methods, the figure has been reduced to 50% or even less. Many oil fields that had been abandoned have been brought back into production. When a field is reworked in this way, it is called secondary recovery.

More efficient recovery techniques have led to an increase in the proved reserves of petroleum which refers to the amount of oil in the ground that will be recovered by known technology. Ultimate reserves refers to the amount of oil that has been discovered.