(c) Solution gas drive. Crude oil has a certain percentage of gas in solution, which is the result
of great pressures under which the crude oil naturally exists. As the gas is released from the oil, it expands and
forces the oil to the production well. This principle is best illustrated by taking a can of soda and shaking it up,
then opening it. The carbon dioxide in the soda is released from the liquid and forces the soda out of the can.
(2) Enhanced Recovery.
Enhanced recovery consists of two production types: secondary and
(a) Secondary recovery. Once the natural forces are consumed in production, some outside force
must be added to allow oil production to continue. Under the category of secondary recovery there are two
methods to continue production.
1 Water flooding. In this method, water is injected into the formation through selected
wells mid oil is removed from the surrounding wells until water production in the oil-producing wells becomes
excessive. Various patterns are used for location of injection and producing wells to maintain the most efficient
2 Gas injection. In this method, gas is injected into the gas cap of the formation to
maintain pressure on the oil-bearing zone. By maintaining the pressure above the oil zone, production can
(b) Tertiary recovery. The listing of various tertiary/enhanced oil recovery techniques, which
follows, includes the more common methods, which were practiced and are being investigated. The degree to
which these methods are currently studied has been greatly reduced in view of the low cost per barrel of crude.
We will briefly discuss three thermal methods and the concept of using miscible fluids.
1 In-situ combustion produces heat energy by burning some of the oil within the reservoir
rock itself. Air is injected into the reservoir, and a heater is lowered into the well to ignite the oil. The resulting
combination of gas, steam, and hot water moves the oil from the injection well to the producing wells.
2 Steam stimulation (Huff and Puff). This thermal method used each well as both the
injection and the production well. First, high pressure steam is injected directly into the production zone for
several days or weeks. After injection, the reservoir area around the well is allowed to soak for additional days or
weeks. After the soak period, the well is brought into production to recover the heated and thinner oil and hot
3 Steam flooding uses separate injection wells and production wells to improve both the
rate of production and the amount of oil that will ultimately be produced. Heat from the injected steam reduces
the viscosity of the oil as the injected fluid drives the oil from the injection well to the production well.
4 Miscible displacement. The miscible nature of fluids refers to the ability of certain fluids
to mix together. Fluids that are miscible with oil are much more effective than either water or gas to drive in
displacing oil from the region they contact. Light hydrocarbons, carbon dioxide, and nitrogen have shown the
most promise, but these still require extensive research and field-testing.
h. Reservoir stimulation methods. After all recovery methods have been economically exhausted, the
petroleum engineer can attempt to recover any remaining oil in place through stimulation techniques. Stimulation
is altering the properties of the petroleum reservoir such that the oil is allowed to move more freely. Two means
of stimulation are: