CA2173414C

CA2173414C - Oil production well and assembly of such wells

Info

Publication number: CA2173414C
Application number: CA 2173414
Authority: CA
Inventors: Bruce Martin Escovedo; Menno Hartemink; Willem Marinus Schulte
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1995-04-07
Filing date: 1996-04-03
Publication date: 2007-11-06
Anticipated expiration: 2016-04-03
Also published as: CN1079887C; EA199600016A3; EA000057B1; CN1140227A; CA2173414A1; EA199600016A2

Abstract

An oil production well comprises an upwardly dipping or substantially horizontal inflow section such that a J--or L-shaped well is created. Hot fluid, such as steam, is injected in the region of the toe of the well such that the injected hot fluid is induced to flow together with the produced crude oil into the well, thereby heating up the inflow section of the well and stimulating the flow of crude oil into and through said inflow section.

Description

OIL PRODUCTION WELL AND ASSEMBLY OF SUCH WELLS

The invention relates to an oil production well and to an assembly of such wells.
It is known in the art to stimulate the recovery of viscous oil from underground oil bearing formations by injecting a hot fluid, such as steam, into the formation, thereby reducing the in-situ viscosity of the crude oil.
Thermally enhanced oil recovery processes where steam is employed to reduce the in-situ viscosity of the crude oil within the pores of a oil bearing formation are disclosed in US patent specification Nos. 3,994,340;
4,344,485; 4,465,137 and 5,046,559.
A problem encountered with steam drive methods is that the injected steam has a much lower viscosity than the crude oil, even after heating thereof, so that once there is a break-through of steam into the production well, this well will produce mainly steam and water stemming from condensed steam together with very little crude oil.
Steam has a lower density than crude oil. Therefore, steam injection will create a pocket of steam at the top of the oil bearing formation. Hence, if oil is produced via a conventional vertical well the break-through of steam will typically occur at the top of the inflow section of the well and the operator will plug off the upper part of the inflow section such that fluids will only flow into the lower part thereof.
US patent specification No. 4,344,485 discloses in Figure 6 a steam injection method where steam is injected into a tar sand deposit above a horizontal inflow section of a production well such that there are separate steam and oil flow paths within the pores of the formation and mobilized heavy oil is induced to drain from the formation towards the horizontal inflow section of the well.

It is an object of embodiments of the present invention to provide an oil production well in which oil production is stimulated by injection of a hot fluid, such as steam, but which is less sensitive to the detrimental effects of a break-through of the injected hot fluid than the prior art production systems.

Accordingly, in on aspect of the invention, there is provided an oil production well comprising an upwardly dipping or substantially horizontal inflow section via which crude oil flows from an oil bearing formation into the well and an injector well or conduit for injecting a hot fluid in the region of a toe of the inflow section such that the injected hot fluid is induced to flow through at least part of said inflow section, thereby transferring heat to the crude oil which is present in said inflow section and the surrounding formation.

In a preferred embodiment of the well according to the invention the well is substantially J-shaped and the inflow section forms a foot of the well.

In the well according to the invention the flow of the hot injection fluid together with the produced crude oil through the inflow section of the well has the advantage that primarily the inflow section and surrounding formation are heated which will stimulate the inflow of crude oil into and through the well. A J-shaped well configuration is attractive since the updip orientation of the toe of the well will provide a natural barrier against a steam break-through.

- 2a -In many wells for the production of viscous crude oils a pump is present for pumping the crude oil to the surface.

In that case the pump in the well according to the invention will be present in the region of a heel of said inflow section and the hot fluid injection means comprise a steam injection system which is adjustable to inject steam in such a quantity and at such a pressure and temperature that the steam condenses before the entry of the pump and the resulting mixture of hot water and crude oil has a pressure below the steam flash point at the conditions at the entry of the pump.
In order to allow heating of the inflow section along its whole length it is furthermore preferred that the hot fluid is injected via an injection well in the region of the toe of the inflow section of the production well.
The invention also relates to a well assembly for producing viscous oil from an underground oil bearing formation.
The assembly comprises a hot fluid injection well and a plurality of oil production wells. The toes of the inflow sections of these production wells are located at substantially equal distances from the injection well and extend in a substantially radial direction away from the injection well. This star-shaped well configuration ensures an uniform distribution of the injected hot fluid over the horizontal sections of the production wells and creates an efficient stimulation system. In the system a single injection well is able to warm-up the inflow sections of a plurality of production wells that extend a substantial distance away from the injection well.
These and other objects, advantages and embodiments of the well and well system according to the invention will become apparent from the accompanying claims, abstract and drawing in which Fig. 1 shows a schematic vertical cross-section of a well system and wells according to the invention.

In Fig. 1 there is shown a central injection well 1 for injecting hot fluid in the form of steam into an underground viscous oil bearing formation 2 as illustrated by arrows I. Apart from the injection well 1 there are two J-shaped production wells 3 according to the invention which comprise substantially horizontal or inclined inflow sections 3A. The sections 3A are perforated or equipped by a slotted liner to allow the inflow of fluids from the surrounding formation as illustrated by arrows II.
The injected steam will form a pocket of steam against the top of the oil bearing formation 2 thereby heating up the formation 2, decreasing the viscosity of the crude oil within the pores of the formation 2 and driving the thus mobilized crude oil towards the inflow sections 3A of the production wells 3.
The present invention is based on the insight that if steam or still hot condensate is permitted to flow together with the mobilized crude oil into the regions of the toes 4 of the inflow sections 3A it will warm-up the inflow sections 3A and stimulate the inflow of crude oil into the wells 3.
The flow rate and pressure of the injected steam are adjusted such that at the entry of the downhole pump 5, which is located in the elbow of each well 3, the produced mixture of crude oil and condensate has a pressure below the steam flash point in order to avoid that the condensate would re-evaporate at the entry of the pump and create a vapour lock.
In the event that steam would tend to bypass the crude oil in one of the wells 3 and this well would produce a mixture with a too high water cut and/or at a too high temperature the toe of the inflow section 3A is plugged to reduce the steam intake. Instead of or in addition to such plugging back of the toe 4 of a well 3 the quantity and pressure of injected steam may be reduced in order to reduce the water cut of the produced mixture.
It will be understood that the presence of an upwardly dipping toe 4 in each well 3 will considerably reduce the risk of a steam break-through in the event that steam or condensate is permitted to flow into the well 3.
However, if necessary, substantially horizontal inflow sections could be employed if these sections are of sufficient length to ensure that the steam will condensate within these horizontal sections and the pressure of the produced mixture of crude oil and condensate has a pressure below the steam flash point at the intake of the downhole pump.

Claims

1. An oil production well comprising an upwardly dipping or substantially horizontal inflow section via which crude oil flows from an oil bearing formation into the well and an injector well or conduit for injecting a hot fluid in the region of a toe of the inflow section such that the injected hot fluid is induced to flow through at least part of said inflow section, thereby transferring heat to the crude oil which is present in said inflow section and the surrounding formation.

2. The oil production well of claim 1, wherein the well is substantially J-shaped and the inflow section forms a foot of the well.

3. The oil production well of claim 1 or 2, wherein a pump for pumping crude oil to the earth surface is present in the region of a heel of said inflow section and the hot fluid injection means comprises a steam injection system which is adjustable to inject steam in such a quantity and at such a pressure and temperature that the steam condenses before the entry of the pump and the resulting mixture of hot water and crude oil has a pressure below the steam flash point at the conditions at the entry of the pump.

4. The oil production well of claim 1, 2 or 3, wherein an injection well is present for injecting hot fluid into the oil bearing formation in the region of the toe of the inflow section of the oil production well.

5. A well assembly for producing viscous oil from an underground oil bearing formation, the assembly comprising a central injection well and a plurality of oil production wells according to claim 4, wherein the toes of the inflow sections of the production wells are located at substantially equal distances from the injection well and said inflow sections extend in a substantially radial direction away from the injection well.