Production

After drilling has located a reservoir of oil or natural gas, the resource has to be brought to the surface. Oil is not drawn from underground lakes. Rather, oil is contained in the pores and fractures of certain sedimentary rocks in the same way that water is held in a sponge. In mature producing areas such as the North Sea, recovering more oil and gas from old wells is a demanding job. Getting the most petroleum, at the least cost, is also a key challenge in new production areas such as the Caspian Sea offshore projects.

The vast hydrocarbon deposits of the Canadian oil sands pose additional, unique problems for scientists and engineers as they seek more efficient and economical ways to recover the tar-like bitumen (petroleum in semi-solid or solid forms).

The primary method in extracting oil is to use simple mechanical pumps to raise oil to the surface. There are a number of methods that are used to improve primary recovery. The most common is infill drilling, which involves drilling more wells into the same pool so the oil does not have to travel as far through the rock to reach a wellbore. Directional wells are often used for infill drilling. More than one directional well can be drilled from a common platform.  Horizontal drilling, which extends the wellbore into a much larger portion of the oil-bearing formation, has been employed since the late 1980s to improve production and enhance recovery.

Further oil production can be obtained by injecting water ("waterflooding") or natural gas to maintain reservoir pressure and push oil out of the rock. This is called secondary recovery.
More advanced methods are referred to as tertiary recovery. The most common tertiary recovery method for light and medium crude oil is miscible flooding. In this procedure, natural gas liquids (ethane, propane and butane) are injected into special injection wells. When dissolved, these liquids reduce surface tension and viscosity to help release the oil from the reservoir rock.

In heavy oil and in-situ bitumen production, enhanced recovery generally involves the application of heat, most commonly by steam injection. Major improvements in heavy oil and bitumen recovery have been achieved by steam assisted gravity drainage (SAGD) which uses parallel pairs of horizontal wells for steam injection and oil recovery.

Even with all these techniques, the average recovery in the light oil fields is a little more than 30% of the original oil. The remaining resource represents billions of cubic metres of oil that has been discovered but cannot be produced economically with existing technology.