Abstract An oil miscible gas such as carbon dioxide is injected into a subterranean oil reservoir to maintain a reservoir pressure near the critical pressure of the gas. Under predetermined conditions of temperature and pressure the miscible gas-crude oil mixture exhibits a three-phase vapor-liquid phenomena which enhances the recovery of oil from the subterranean reservoir. A miscible gasrich liquid phase is formed between the oil-rich liquid phase and miscible gas-rich vapor phase and exhibits a density and viscosity intermediate between that of the oil and gas regions. This phenomenon creates a unique fluid distribution and mobility relationship which provides for a significant increase in the efficiency of the displacement of the oil from the gas-swept reservoir.
The process of claim 1 further comprising: a. introducing an inert fluid after a bank of carbon dioxide has been formed; and b. driving the three-phase region and bank of carbon dioxide through the reservoir with the inert fluid.
Claim 2
Dependent Claim
215 words
In a miscible displacement process for the recovery of oil, of the type wherein miscible gas is introduced into a subterranean oil reservoir under pressure so as to form a bank of miscible gas which dissolves in and renders mobile the oil contained therein and drives the contacted oil to a point wherein it is removed to the earth''s surface, the improvement which comprises introducing the miscible gas, consisting essentially of a gas selected from the group consisting of ethane and a mixture of ethane and carbon dioxide, under the conditions of pressure and temperature so that a three-phase equilibrium is formed between the miscible gas and the reservoir fluid, comprising a vapor phase rich in the miscible gas being formed at the furthest extent of the leading front of the bank of miscible gas injected, a second phase being a liquid phase rich in the miscible gas and exhibiting a density and viscosity intermediate to the two other phases and formed therebetween, and a third phase being a liquid phase rich in the components of the reservoir fluid and in contact therewith so that as further miscible gas is introduced into the reservoir, the three-phase region moves through the reservoir, thereby contacting virgin oil, dissolving therein, lowering its viscosity and rendering it more mobile.
Claim 3
Dependent Claim
18 words
The process of claim 3 in which the miscible gas is a mixture of carbon dioxide and ethane.
Claim 4
Dependent Claim
39 words
The process of claim 3 further comprising: a. introducing an inert fluid after a bank of miscible gas, has been formed; and b. driving the three-phase region and bank of miscible gas through the reservoir with the inert fluid.
Claim 5
Dependent Claim
18 words
The process of claim 5 in which the miscible gas is a mixture of carbon dioxide and ethane.