EP2009231A1

EP2009231A1 - Method of producing crude oil

Info

Publication number: EP2009231A1
Application number: EP07111358A
Authority: EP
Inventors: Wilhelmus Hubertus Paulus Maria Heijnen
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2007-06-29
Filing date: 2007-06-29
Publication date: 2008-12-31

Abstract

A method of producing crude oil, comprising:
a) drilling a well (1) traversing a crude oil containing formation (2);
b) creating a cavity (8) in the vicinity of the well;
c) creating a flow channel (3A,3B) between the cavity and the well;
d) inducing crude oil (20) to flow from the crude oil containing formation into the cavern the flow channel a section of the well, which is equipped with a valve (13);
e) closing the valve when a substantial portion of the cavity is filled with crude oil;
f) injecting water into the cavity, thereby inducing crude oil to flow from the cavity via the flow channel and the well to a wellhead (15) at the earth surface;
g) interrupting water injection into the cavity when a substantial portion of the cavity is filled with water;
h) pumping water from the cavity and filling at least a substantial portion of the cavity with a gaseous fluid;
i) opening the valve and repeating steps d)-h).
The method may make use of a one way valve (13) nitrogen and a salt layer (4).

Description

BACKGROUND OF THE INVENTION

The invention relates to a method of producing crude oil from a crude oil containing formation.
In many crude oil containing formations the pore pressure is too low to lift the produced crude oil to surface. In such cases artificial lift methods are often used, such as gas-lift and or electrical submersible pumps (ESP's).
Gas lift injection systems and ESP's comprise wear prone components that require regular inspection, maintenance and/or replacement, which is a time consuming and expensive procedure, which may render crude oil production unecomical, in particular if the crude oil comprises fines and/or acidic components, such as hydrogen sulphide and/or carbon dioxide.
If the produced crude oil contains more than a few weight percent of hydrogen sulphide then the estimated lifetime of an ESP may be less than 500 days, after which a work over is required to replace the pump.
During the work over the wellhead needs to be opened and extensive precautions need to be made to prevent hydrogen sulphide to flow from the well into the atmosphere.
It is an object of the present invention to provide a method of producing crude oil from a low pressure crude oil containing formation without the need for wear prone downhole artificial lift equipment, such as ESP's and/or lift gas injection valves.
It is a further object of the present invention to provide a method of producing sour crude oil from a sour crude oil containing formation, such that the risk of escape of sour gases, such as hydrogen sulphide, from the well into the atmosphere, in particular during work over operations, is reduced.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method of producing crude oil, comprising:

a) drilling a well traversing a crude oil containing formation;
b) creating a cavity in the vicinity of the well;
c) creating a flow channel between the cavity and the well;
d) inducing crude oil to flow from the crude oil containing formation into the cavern the flow channel and a section of the well, which is equipped with a valve;
e) closing the valve when a substantial portion of the cavity is filled with crude oil;
f) injecting water into the cavity, thereby inducing crude oil to flow from the cavity via the flow channel and the well to a wellhead at the earth surface;
g) interrupting water injection into the cavity when a substantial portion of the cavity is filled with water;
h) pumping water from the cavity and filling at least a substantial portion of the cavity with a gaseous fluid;
i) opening the valve and repeating steps d)-h).

The cavity may be created in one or more salt layers surrounding the well in an upper section of the well located between the crude oil containing formation and the wellhead, for example by injecting water from the upper section of the well through perforations in a well casing into one or more of the salt layers, thereby leaching salt into the injected flux of water.
The produced crude oil may be associated with gas comprising hydrogen sulphide and the associated gas may be treated in a vessel containing a hydrogen sulphide scavenger, such as a sulferox scrubber, which vessel is located in a gas transportation conduit located between the wellhead and the flare.
During step h) water may be pumped from the cavern by inserting a hose or other conduit carrying at its lower end a pump through the wellhead into the upper section of the well, and pumping water from upper section of the well until the upper section of the well and the flow channel and cavity are substantially dry.
Furthermore during step h) an oxygen depleted inert gas may be injected into the upper section of the well, which oxygen depleted inert gas may comprise at least 90 vol% nitrogen.
The valve in the wellbore between the oil containing earth layer and the salt cavern may be a one way valve, which permits fluid to flow from a lower section of the well traversing the crude oil containing earth layer, and the upper section of the well, and which inhibits fluid to flow from the upper into the lower section of the well.
These and other features, embodiments and advantages of the method according to the invention are described in the accompanying claims, abstract and the following detailed description of a preferred embodiment in which reference is made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 shows how one or more caverns are leached into one or more salt layers around an upper section of a well;
FIG.2 shows how crude oil is produced from a crude oil containing formation into a lower section of the well and transported via the well into the cavern surrounding the upper section of the well;
FIG.3 shows how after closing a valve between the lower and upper sections of the well water is pumped into the upper section of the well thereby lifting crude oil from the cavern to the wellhead; and
FIG.4 shows how after lifting substantially all crude oil from, water is pumped from and/or nitrogen is pumped into, the cavern and upper section of the well.

DETAILED DESCRIPTION OF DEPICTED EMBODIMENTS OF THE INVENTION

FIG.1 shows a wellbore 1 that penetrates a sour crude oil, methane (CH₄), hydrogen sulphide(H2S) and water containing earth layer 2. A casing 3 has been cemented within the wellbore 1 such that sour crude influx from the earth layer into the wellbore 1 is inhibited.
The casing 3 comprises a perforated section 3A, 3B that is located in a region above the crude oil containing earth layer 2 where the wellbore 1 traverses a series of salt layers 4, which are also identified as halite layers.
A water injection tube 6 has been inserted into the wellbore 1, which tube 6 carries a movable packer 7 near its lower end. The packer is located adjacent to the perforated section 3A, 3B of the casing 3, such that when fresh water is injected through the water injection tube 6, the injected water is pumped through the perforations 3A below the movable packer 7 into the lowermost salt layer 4, thereby leaching a cavity 8A in this salt layer 4 and the water and leached salt mixture returns to surface through the perforations 3B above the packer 7 and through an annular space 9 between the casing 3 and water injection tube 6, as indicated by arrows 10.
By gradually pulling the water injection tube 6 and packer 7 up through the perforated region of the casing 3 a series of three caverns 8A, 8B and 8C are leached into the salt layers 4, which caverns are then merged by placing the packer 7 adjacent to the thin impermeable earth layers 11A and 11B and injecting water at high pressure through the water injection tube 6 into the cavern 8A or 8B below the impermeable lay 11A,11B, until the impermeable layer 11A,11B collapses and a single cavity 8 is created around the perforated section of the casing 3.
Fig. 2 shows the completed wellbore 1 after retrieval of the water injection tubing 6, wherein a mixture of sour crude oil, CH₄ , H_SS and water flows through perforations 12 in the casing adjacent to the sour crude oil, CH₄ , H_SS and water containing earth layer 2. The produced mixture flows through a one way check valve 13 up through the wellbore 1 and through the perforated casing sections 3A and 3B into the cavity 8 in the salt layer(s) 4 as illustrated by arrows 14.
The gaseous components CH₄ and H₂S predominantly flow up through the wellbore 1 via the well head 15 and a gas discharge conduit 16 into a gas treating unit 17 in which H₂S is removed from the produced methane CH₄ and from which the purified methane CH₄ may be discharged into a gas production pipe or a flare 18.
The cavity 8 performs as a gravity separation vessel in which crude oil and water will be separated by gravity forces and an upper layer of crude oil 20 will float on top of a lower layer of water (H₂O) 21.
FIG.3 shows how a water injection tube 30 is inserted through the wellhead 15 into the wellbore 1 such that water is injected through the perforated sections 3A, 3B of the casing 3 into the cavity 8. The one way check valve 13 prevents that the injected water reaches the perforations 12 in the lower inflow region of the wellbore 1.
The injected flux of water pushes the crude oil layer 20 that floats on top of the water layer 21 to flow up through the wellbore 1 via the wellhead 15 into a crude oil discharge conduit 31. The discharge conduit 31 may be connected to an oil production pipeline or to a crude oil collecting tank, from which the collected crude oil may be discharged by a road tanker.
FIG.4 shows how after discharging the crude oil from the wellbore 1 water is pumped out of the wellbore 1 by a submerged pump 41, which is suspended at the lower end of a water discharge hose 42, while at the same time nitrogen (N₂) is injected into the wellbore 1 via a nitrogen feed conduit 43, such that after removal of the water the cavern is substantially filled with nitrogen (N₂) at an ambient atmospheric pressure of about 1 bar.
After removal of the submerged pump 41 and hose 42 production of sour crude oil, gas and water from the earth layer 2 is resumed in the manner as illustrated in FIG.2 until the cavern has been filled again with crude oil and water, whereupon production is interrupted and water is injected into the wellbore 1 above the one way check valve 13 and cavern 8 as illustrated in FIG.3 and subsequently water is pumped out of the wellbore 1 and cavity 8 as illustrated in FIG.4.
The cyclic production of crude oil and water into the cavern 8 and subsequent injection of water and nitrogen into the cavern 8 as illustrated in FIG.2-4 is cyclically repeated until at least a substantial part of the crude oil has been produced from the earth layer 2.
It will be understood that the method according to the invention permits production of crude oil such that a relatively low hydrostatic pressure is maintained in the wellbore 1 and a low bottom hole pressure (BHP) permits production of a large flux of crude oil from the crude oil containing earth layer 2, without using a corrosion prone permanently installed electrical submersible pump(ESP).

Claims

A method of producing crude oil, comprising:
a) drilling a well traversing a crude oil containing formation;

b) creating a cavity in the vicinity of the well;

c) creating a flow channel between the cavity and the well;

d) inducing crude oil to flow from the crude oil containing formation into the cavern the flow channel and a section of the well, which is equipped with a valve;

e) closing the valve when a substantial portion of the cavity is filled with crude oil;

f) injecting water into the cavity, thereby inducing crude oil to flow from the cavity via the flow channel and the well to a wellhead at the earth surface;

g) interrupting water injection into the cavity when a substantial portion of the cavity is filled with water;

h) pumping water from the cavity and filling at least a substantial portion of the cavity with a gaseous fluid;

i) opening the valve and repeating steps d)-h).
The method of claim 1, wherein the cavity is created in one or more salt layers surrounding the well in an upper section of the well located between the crude oil containing formation and the wellhead.
The method of claim 2, wherein the cavity is created by injecting water from the upper section of the well through perforations in a well casing into one or more of the salt layers, thereby leaching salt into the injected flux of water.
The method of claim 2, wherein during step f) water is injected into the cavern by inserting a hose through the wellhead into the upper section of the well.
The method of claim 1, wherein the wellhead is provided with a flare for flaring gas dissolved in the produced crude oil.
The method of claim 5, wherein the gas is contains hydrogen sulphide and the gas is treated in a vessel containing a hydrogen sulphide scavenger, such as a sulferox scrubber, which vessel is located in a gas transportation conduit located between the wellhead and the flare.
The method of claim 2, wherein during step h) water is pumped from the cavern by inserting a hose or other conduit carrying at its lower end a pump through the wellhead into the upper section of the well, and pumping water from upper section of the well until the upper section of the well and the flow channel and cavity are substantially dry.
The method of claim 1, wherein during step h) an oxygen depleted inert gas is injected into the upper section of the well.
The method of claim 8, wherein the oxygen depleted inert gas comprises at least 90 vol% nitrogen.
The method of claim 1, wherein the valve is a one way valve, which permits fluid to flow from a lower section of the well traversing the crude oil containing formation, and the upper section of the well, and which inhibits fluid to flow from the upper section into the lower section of the well.