Wells – Processes – Distinct – separate injection and producing wells
Reexamination Certificate
1999-04-13
2001-07-24
Neuder, William (Department: 3672)
Wells
Processes
Distinct, separate injection and producing wells
C166S303000, C166S369000
Reexamination Certificate
active
06263965
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to in situ recovery of oil from tar sand located in a subsurface formation. More particularly, the invention provides a method for recovering oil from a subsurface tar sand formation by means of a unique steam injection system.
There are many methods for recovering a resource, such as tar sand, from beneath the earth surface. Where there is little overburden, surface mining techniques have been widely employed. However, when the overburden is thick or the ratio of overburden to tar sand formation thickness is high, then surface mining is no longer economical. Many in situ recovery methods have been proposed over the years. Typically, wells are drilled from the earth surface down into the tar sand formation. These tar sand formations in their normal or undisturbed state are very viscous and immobile. Many different techniques have been developed to establish both a communication path through the heavy, highly viscous bitumen-filled sand and an efficient method to recovery the bitumen from the sand. These methods include such things as steam injection, solvent flooding, gas injection, etc. Such processes generally involve the heating of the tar sand formation to reduce the viscosity of the formation, thereby allowing removal of the resource from the formation in flowable form by hydraulic means or gravity flow.
U.S. Pat. No. 4,160,481 uses a plurality of bore holes radially extending from a central bore hole to inject steam into the tar sand formation. Steam is injected into some bore holes to drive the oil into the remaining bore hole where it is collected.
In Turk et al., U.S. Pat. No. 4,160,481, a method is described in which perforated radial tubes extend laterally into the formation from a central bore hole. That system uses a cyclic steam injection procedure. After a number of steam injection/production cycles, the process can be converted to a continuous steam drive where steam is continuously injected into one radial and oil is produced from another radial.
Bouck et al., U.S. Pat. No. 4,463,988, describes an in situ recovery system for a tar sand deposit in which a network of horizontal production tunnels and connecting horizontal bore holes are provided. This is a complex structure and a difficult and expensive one to install and operate.
Bielstein et al., U.S. Pat. No. 3,386,508, describes a system for recovering oil in which a plurality of directional (slant) wells are drilled from the surface to intersect a central vertical well within an oil bearing formation. Both the directional wells and the vertical well bore communicate fluidly with the oil bearing formation.
In Renard et al., U.S. Pat. No. 5,016,710, another system for recovering oil is described having a plurality of slant wells drilled from the surface to cooperate with a central vertical well within an oil bearing formation. With this design, steam may be injected into the oil bearing formation either from the central vertical well or from the plurality of slant wells.
It is an object of the present invention to provide an improved system for recovering normally immobile hydrocarbon oil from a subsurface tar sand formation by steam injection.
SUMMARY OF THE INVENTION
This invention in its broadest aspect relates to a thermal method for recovering normally immobile hydrocarbon oil from a subsurface tar sand deposit comprising: (a) establishing at least one substantially vertical production bore hole extending from the surface of the earth to at least the bottom of said subsurface formation; (b) providing a plurality of bore holes extending downwardly from the surface of the earth through the tar sand formation to substantially the bottom thereof and then substantially horizontally at or near the bottom of the tar sand formation and converging radially inward to each said bore hole, each said radial bore hole containing a perforated or slotted tube; (c) continuously injecting steam downwardly through said perforated or slotted tubes whereby the steam discharges through the perforations or slots and into the tar sand formation to reduce the viscosity of the normally immobile oil, with a substantial proportion of the steam being injected into the formation via the portion of each tube extending downwardly through the tar sand formation whereby the steam reduces the viscosity of the normally immobile oil over an area extending substantially between the perforated tube and the top of the tar sand formation with this viscosity reducing area expanding radially and moving axially inwardly toward the vertical production bore hole thereby creating an expanding generally conical-shaped production chamber; and (d) draining the less viscous oil and steam condensate thus obtained downwardly by gravity to the bottom of the production chamber and then through the horizontal tubes into the bottom of the vertical production bore hole for collection.
An important feature of this invention is that the steam is injected into the radially converging perforated or slotted bore holes from the surface. In this manner, the injected steam is able to contact the entire vertical section of the tar sand deposit during the initial stages of steam injection, and the maximum steam pressure is at the greatest distance away from the vertical production bore hole. Also, each radially converging bore hole is continuous from the surface to the vertical production bore hole and is simultaneously used for both steam injection and oil production.
This provides important advantages. Firstly, because the greatest heat and pressure from the steam is provided at the greatest distance from the vertical production bore hole and this heat and pressure gradually decrease along the length of each converging radial tube, the result is that oil is removed from the tar sand formation in such a manner that the greatest amount is removed nearest the steam injection end (the furthest distance away from the vertical production bore hole) with decreasing amounts being removed inward along the length of each converging radial tube. As a result, the production areas within the tar sand formation develop a generally conical shape which conforms to the shape of the tar sand formations between the radial tubes thereby maximizing the amount of oil that can be extracted from a tar sand formation by means of a central bore hole with laterally converging radial tubes.
It is also advantageous according to this invention to have a major proportion of the perforated or slotted tubes within the tar sand formation travel horizontally along the bottom of the formation. Thus they sit immediately above an impervious underlayer. This provides a greatly improved extraction efficiency. The injected steam tends to rise within the formation and the use of tubes arranged in both a radial and horizontal configuration means that the maximum possible oil production is achieved within a production area.
The generally conical expanding production zone extends down to the horizontal perforated or slotted pipe and becomes a steam chamber. Thus, the oil of reduced viscosity that is being released from the tar sand formation flows by gravity downwardly through this production zone or steam chamber and into the horizontal perforated or slotted pipe. Because of the higher steam pressure at the outer ends of the perforated tubes, this pressure gradient assists gravity flow in driving the extracted oil within the perforated tubes to the central vertical production bore hole for recovery. A plurality of these central vertical production bore holes with inwardly converging radial tubes may be arranged as an array in a tar sand formation, and by operating such installations in a simultaneous manner, an entire tar sand field can be drained in a systematic manner.
The central vertical production bore hole preferably extends a distance down into an impervious formation underlying the tar sand formation to thereby form a sump for collecting the less viscous (flowable) oil. This flowable oil is pumped from the sump to the surface by conventional oil field p
Jespersen Paul J.
Kristoff Brian J.
Schmidt Brian H.
Neuder William
Tecmark International
Walker Zakiya
LandOfFree
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