Heavy Oil

heavy oil and tar sand, crude oils below 20° on the American Petroleum Institute (API) gravity scale that require mining or thermal recovery. Although the lighter conventional crudes are often waterflooded to enhance recovery, this method is essentially ineffective for heavy crudes between 20° and 10° API gravity, and thermal recovery becomes necessary. Heavy crude oils have enough mobility that, given time, they will be producible through a well bore in response to thermal recovery methods. Tar sands, which are less than 10° API gravity and contain immobile bitumen, will not flow into a well bore even under thermal stimulation and thus require mining.