1. Field of the Invention
This invention relates to a steam flooding process for the recovery of hydrocarbons from a subterranean formation. More particularly, this invention relates to a recovery process in which hydrocarbons driven toward a production well by means of a fluid, such as steam or a mixture of steam and carbon dioxide, which is injected into the formation via an injection well are coproduced from a lower horizon of the formation via the production well along with water introduced into the upper horizon of the formation.
2. Prior Art and Background
The production of hydrocarbon products is usually achieved by drilling into a hydrocarbon-bearing formation and employing one of the art-recognized recovery methods for the recovery of hydrocarbons therein. Present recovery techniques, however, usually result in the recovery of only a minor portion of the petroleum materials present in the formation and this is particularly true with reservoirs of viscous crudes. Even when employing improved secondary recovery practices as much as 50-75 percent of the original hydrocarbon may be left in place and even more in the case of viscous hydrocarbon reservoirs.
A variety of processes well known in the art, such as water flooding, steam flooding, miscible flooding, etc. have been employed after natural drive of the reservoir has been depleted in order to recover additional oil from the formation. The application of these techniques which are sometimes referred to as secondary recovery methods permits additional hydrocarbons to be removed from the partially depleted formations. One of the more widely practiced secondary recovery methods is that of the so-called steam flooding process. Steam flooding is notably well-suited for secondary recovery operations since the energy contained in the fluid effectively reduces the viscosity of the hydrocarbons and permits production thereof. In order to realize the maximum viscosity reduction of the hydrocarbons, the injected steam should impart the maximum heat to the formation, as is consistent with economical steam generator design, and provide a uniform penetration of the formation.
Despite the advantages of steam flooding operations, under certain circumstances present-day steam flooding techniques fail in many instances to permit recovery of large quantities of hydrocarbons contained in the formation. As a result, a number of modified steam injection processes have been proposed including a "push-pull" technique and throughput methods which have resulted in some instances in additional significant recoveries of crude oil from the reservoirs.
One of the main problems faced in the recovery of hydrocarbons by steam flooding is early breakthrough of steam into the production well since at that time no more oil is produced. Breakthrough generally is caused by the tendency of the steam to move updip and to flow only through the upper part of the formation.
There is a definite need in the art, therefore, for a steam flooding process in which steam breakthrough into the production well is prevented thus greatly increasing the amount of oil recovered.
Another disadvantage of steam flooding is that some distillation in the formation takes place with the result that lighter, more volatile solutions of the in-place hydrocarbons are recovered leaving behind the more viscous oil with an increased asphaltene and aromatic content. Thus, the nature of the residual oil left behind after an initial period of steam flooding of a formation is probably different from that of the original oil composition in place because of distillation effects, etc. and the efficiency of the removal process gradually declines.
Accordingly, it is an object of the present invention to overcome the disadvantages of the prior art steam flooding process by providing an efficient, improved steam flooding method for hydrocarbon recovery.