U.S. patent application number 10/477241 was filed with the patent office on 2004-09-16 for gas lift method with surfactant injection.
Invention is credited to Ramachandran, Sunder.
Application Number | 20040177968 10/477241 |
Document ID | / |
Family ID | 23119125 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040177968 |
Kind Code |
A1 |
Ramachandran, Sunder |
September 16, 2004 |
Gas lift method with surfactant injection
Abstract
Disclosed is a method for optimizing gas lift operations in the
production of crude oil. A surfactant is injected with the lift gas
into the an oil well such that the surface tension between the lift
gas and the formation fluid being produced is reduced and/or a lift
gas-formation fluid foam is formed. The reduction in surface
tension and/or foam formation increases the efficiency of the lift
gas for lifting the formation fluid to the surface. The surfactant
is selected to minimize corrosion. Exemplary surfactants include
those in the group consisting of ethoxylated alcohols and all salts
thereof, ethoxylated alkyl phenols and all salts thereof,
ethoxylated amines and all salts thereof, alkyl ether sulfates and
all salts thereof, all betaines and all salts thereof, all
sultaines and all salts thereof, perfluorinated polyurethanes, and
mixtures thereof.
Inventors: |
Ramachandran, Sunder;
(Sugarland, TX) |
Correspondence
Address: |
Stephen A Littlefield
Baker Petrlolite Division
Bakers Hughes Incorporated
12645 West Airport Blvd
Sugar Land
TX
77478
US
|
Family ID: |
23119125 |
Appl. No.: |
10/477241 |
Filed: |
November 10, 2003 |
PCT Filed: |
May 15, 2002 |
PCT NO: |
PCT/US02/15531 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60291160 |
May 15, 2001 |
|
|
|
Current U.S.
Class: |
166/372 |
Current CPC
Class: |
C09K 8/584 20130101;
C09K 8/594 20130101; E21B 43/122 20130101 |
Class at
Publication: |
166/372 |
International
Class: |
E21B 043/00 |
Claims
What is claimed is:
1. A method for recovering oil from a gas-lifted oil well
penetrating a subterranean oil-bearing formation, the method
comprising: A) providing a lift gas and a surfactant at an oil well
wherein the oil well penetrates a subterranean oil-bearing
formation and has formation fluids in the well bore; B) injecting a
lift gas into the oil well; and C) injecting a surfactant into the
oil well, wherein i) the surfactant functions to: (a) reduce the
surface tension between the formation fluids and the lift gas; (b)
create a lift gas-formation fluid foam; or (c) both (a) and (b);
ii) the surfactant and lift gas are injected into the oil well at a
depth sufficiently deep to lift formation fluids to the surface;
and iii) the surfactant is selected from the group consisting of
ethoxylated alcohols and all salts thereof, ethoxylated alkyl
phenols and all salts thereof, ethoxylated amines and all salts
thereof, alkyl ether sulfates and all salts thereof, all betaines
and all salts thereof, all sultaines and all salts thereof,
perfluorinated polyurethanes, and mixtures thereof.
2. The method of claim 1 wherein the lift gas is selected from the
group consisting of natural gas, carbon dioxide, methane, ethane,
propane, nitrogen, and mixtures thereof.
3. The method of claim 2 wherein the lift gas is natural gas or
nitrogen.
4. The method of claim 1 wherein the surfactant is prepared using
solvents that do not strip off at the formation temperature or well
operating temperature of gas-lifted oil well.
5. The method of claim 1 wherein the surfactant is selected to have
a temperature stability at or above the formation temperature or
well operating temperature of gas-lifted oil well.
6. The method of claim 5 wherein the formation temperature or well
operating temperature of gas-lifted oil well exceeds 250.degree. F.
and the surfactant is a betaine, alkyl betaine or a salt
thereof.
7. The method of claim 6 wherein the formation temperature or well
operating temperature of gas-lifted oil well exceeds 300.degree. F.
and the surfactant is a betaine, alkyl betaine or a salt thereof.
Description
[0001] This application takes priority from U.S. Provisional Patent
Application Serial No. 60/291,160 filed May 15, 2001, and assigned
to the assignee of this application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of producing crude
oil. The present invention particularly relates to a method of
producing crude oil using a gas lift process.
[0004] 2. Background of the Art
[0005] Oil from oil bearing earth formations is usually first
produced by the inherent formation pressure of the oil bearing
earth formations. In some cases, however, the oil bearing formation
lacks sufficient inherent pressure to force the oil from the
formation upward to the surface. In other cases, the inherent
pressure of an oil-bearing formation can be expended prior to the
recovery of all of the recoverable oil so that when the pressure of
the production zone has been reduced by continued withdrawal, the
well will stop flowing. When this occurs, artificial methods of
lifting the oil from the formation to the surface are usually
employed.
[0006] One method of continuing production is to provide mechanical
pumping operations wherein the pump is located at the surface. In
U.S. Pat. No. 3,963,377 to Elliott, et al., a pneumatically powered
submerged pump for lifting high viscosity oil from an oil well is
disclosed. Another popular method for achieving production from
wells that no longer are capable of natural flow is by the gas lift
method.
[0007] Gas injection into an oil well is a well-known artificial
lift method for facilitating oil recovery from the oil well. This
method is commonly referred to as gas lift recovery or, most often,
simply as a gas lift. A typical gas lift method provides a lift gas
at the surface that is conveyed to a surface wellhead connection
where the lift gas is injected into the casing-tubing annulus of
the well. Upon injection, the lift gas travels down the
casing-tubing annulus to a plurality of specially designed
subsurface gas injection valves that enable the lift gas to enter
the tubing string. The lift gas commingles with the formation
fluids in the tubing string, lifting the formation fluids up the
tubing string to the surface.
[0008] As is taught in U.S. Pat. No. 5,871,048 to Tokar, et al.,
there are significant operational costs associated with gas
injection. In Tokar, a method for automatically determining an
optimum gas rate is disclosed. While determining the optimum gas
flow is an important element in gas lift methods, it is by no means
the only factor that should be considered when optimizing a gas
lift method for recovering oil from an oil well.
[0009] It would be desirable in the art of producing oil from oil
wells to economically produce oil using a gas lift method. It would
be particularly desirable to reduce the cost of producing crude oil
using a gas lift method of recovery. Accordingly, it is desirable
to economically optimize the gas injection lift method such that
the operational costs for the well are balanced with the oil
production revenue from the well.
SUMMARY OF THE INVENTION
[0010] In one aspect, the present invention is a method for
recovering oil from a gas-lifted oil well penetrating a
subterranean oil-bearing formation, the method comprising: A)
providing a lift gas and a surfactant at an oil well wherein the
oil well penetrates a subterranean oil-bearing formation and has
formation fluids in the well bore; B) injecting a lift gas into the
oil well; and C) injecting a surfactant into the oil well, wherein
i) the surfactant functions to: (a) reduce the surface tension
between the formation fluids and the lift gas; (b) create a lift
gas-formation fluid foam; or (c) both (a) and (b); ii) the
surfactant and lift gas are injected into the oil well at a depth
sufficiently deep to lift formation fluids to the surface; and iii)
the surfactant is selected from the group consisting of ethoxylated
alcohols and all salts thereof, ethoxylated alkyl phenols and all
salts thereof, ethoxylated amines and all salts thereof, alkyl
ether sulfates and all salts thereof, all betaines and all salts
thereof, all sultaines and all salts thereof, perfluorinated
polyurethanes, and mixtures thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] In one embodiment, the present invention in a method for
recovering oil from a gas-lifted oil well penetrating a
subterranean oil-bearing formation. The present invention can be
used with any gas lift method known to be useful to those of
ordinary skill in the art of producing oil. For example the method
of the present invention can be used with the gas lift method
disclosed in U.S. Pat. No. 5,871,048 to Tokar, et al.
[0012] In Tokar, a method for automatically determining an optimum
gas injection rate for a gas-lifted oil well is disclosed. The
optimum gas-lift slope for the oil well is initially provided and
stored in the memory of a programmable logic controller. A lift gas
is injected into the well at an initial gas injection rate to
displace a liquid at an initial liquid production rate from the
well. The initial liquid production rate and initial gas injection
rate are stored in the memory. Thereafter, the lift gas is injected
into the well at a first incremental gas injection rate differing
from the initial gas injection rate by a first incremental value.
Additional liquid is displaced from the well at a first incremental
liquid production rate and the first incremental liquid production
rate and first incremental gas injection rate are stored in the
memory. The first incremental slope is determined from the stored
data points and compared to the optimum gas-lift slope. The
procedure is repeated for a second incremental gas injection rate,
wherein the second incremental value is selected as either positive
or negative in response to the comparison of the first incremental
slope and the optimum gas-lift slope. The second incremental slope
is determined from the stored data points and compared to the
optimum gas-lift slope. In response to this comparison, the first
incremental gas injection rate is determined to be the optimum gas
injection rate or the above-recited procedure is repeated for a
third incremental gas injection rate and additional incremental gas
injection rates, if necessary, until an incremental gas injection
rate is determined to be the optimum gas injection rate.
[0013] The method of the present can also be use with less complex
gas lift methods. The present invention can be used with any gas
lift method as long as the gas lift method serves the functions of
lifting formation fluids to the surface which then results in a
lower pressure at the producing strata which in turn results in an
increased inflow of formation fluids into the well bore. In all of
these methods, the gas injection is done a depth sufficient to lift
formation fluid to the surface and allow for the inflow of
additional formation fluid into the well bore. Any combination
equipment and methods can be used with the present invention as
long as it meets these two basic criteria.
[0014] In another embodiment, the present invention is a method for
recovering oil from a gas-lifted oil well including the step of
injecting a lift gas into the oil well. Any lift gas known to be
useful to those of ordinary skill in the art of using gas lift
recovery methods can be used with the present invention. One gas
commonly used as a lift gas with the present invention is natural
gas, preferably that recovered from the same formation as the well
subject to the gas lift method. Other gases can also be used
including those selected from the group consisting of carbon
dioxide, methane, ethane, propane, nitrogen, and mixtures thereof.
Any gas that is not detrimental to the formation, such as oxygen,
can be used with the present invention.
[0015] In yet another embodiment, the present invention is a method
for recovering oil from a gas-lifted oil well including the step of
injecting a surfactant into the oil well. The surfactants useful
with the present invention function to reduce the surface tension
between the lift gas and the formation fluid being lifted to the
surface and/or create a foam of the lift gas and the formation
fluid. This decreased surface tension and or foam formation allows
for a decrease in the density of the formation fluid which results
in an increase in lift efficiency.
[0016] The present invention can reduce the cost of recovery of oil
from a gas-lift oil well in at least two ways. A first way that the
costs can be reduced in recovering oil from a well wherein the rate
of recovery is limited by the amount of gas that can be injected,
is by increasing the amount of formation fluids being recovered per
unit of gas used. With the method the present invention, oil is
recovered more quickly reducing the duration of the maintaining the
well with its incumbent costs.
[0017] A second way that the present invention can reduce
production costs is, in a well wherein the rate of recovery in not
limited by the amount of gas which can be injected, is by reducing
the amount of gas which must be injected. Since the lift gas lifts
more efficiently, less gas is needed to lift the same amount of
formation fluids as compared to a conventional gas lift well
operation. Particularly in applications wherein there is not
sufficient gas available from the formation being produced and
other gasses such as nitrogen or carbon dioxide is being purchased,
this can result in a substantial savings as compared to
conventional gas lift technology. For purposes of the present
application, the term formation fluids means those fluids produced
from a oil bearing subterranean formation including but not limited
to oil, natural gas, water and the like.
[0018] In addition to decreasing the surface tension between the
formation fluid and lift gas, the surfactants useful with the
method of the present invention preferably are non-corrosive. Such
surfactants include, but are not limited to the group consisting of
ethoxylated alcohols and all salts thereof, ethoxylated alkyl
phenols and all salts thereof, ethoxylated amines and all salts
thereof, alkyl ether sulfates and all salts thereof, all betaines
and all salts thereof, all sultaines and all salts thereof,
perfluorinated polyurethane and mixtures thereof.
[0019] The surfactant formulations useful with the present
application, when prepared with a surfactant, are prepared using
solvents that do not strip off at the formation temperature or well
operating temperature. Failure to use such surfactants will leave
residue on the gas lift system choking the system. In the method of
the present invention, the surfactant is preferably formulated
using solvents, if any, which will not leave residue on the gas
lift system.
[0020] Preferably, the surfactants used with the method of the
present invention are thermally stable at the formation temperature
or well operating temperature of the well being treated. Failure to
use such surfactants can lead to the loss of efficiency of the gas
lift system as the surfactants break down. Surfactant break down
products can also cause problem downstream. As such temperatures
can exceed 250.degree. F. (121.degree. C.) and even reach
300.degree. F. (149.degree. C.) and above, it is preferable that
for high temperature environments, the surfactant be a betaine,
alkyl betaine or a salt thereof.
[0021] When the surfactant is an ethoxylated alcohol or a salt
thereof, it preferably has the general formula:
CH.sub.3--(CH.sub.2).sub.n--O--(CH.sub.2--CH.sub.2--O).sub.m--OH
[0022] wherein n and m vary from 1-100.
[0023] When the surfactant is an ethoxylated alkyl phenol or a salt
thereof, it preferably has the general formula:
CH.sub.3--(CH2).sub.n--O--(CH.sub.2--CH.sub.2--O).sub.m--C.sub.6H.sub.5OH
[0024] wherein n and m vary from 1-100.
[0025] When the surfactant is an ethoxylated amine or a salt
thereof, it preferably has the general formula:
CH.sub.3--(CH.sub.2).sub.n--O--(CH.sub.2--CH.sub.2--O).sub.m--NH.sub.2
[0026] where n and m vary from 1-100.
[0027] When the surfactant is an alkyl ether sulfate or a salt
thereof, it preferably has the general formula:
CH.sub.3--(CH.sub.2).sub.n--O--(CH.sub.2--CH.sub.2--O).sub.m--SO.sub.3H
or
CH.sub.3--(CH.sub.2).sub.n--O--(CH.sub.2--CH.sub.2--O).sub.m--SO.sub.3H.NH-
.sub.3
[0028] wherein n and m vary from 1-100
[0029] When the surfactant is a betaine, alkyl betaine or a salt
thereof, it preferably has the general formula:
RN.sup.+(CH.sub.3).sub.2COO.sup.-
or
RNH.sup.+(CH.sub.2).sub.nCH.sub.2COO.sup.-)(CH.sub.2).sub.mCH.sub.2COOH)
[0030] wherein R is a hydrocarbon side chain, and n and m vary from
1-100.
[0031] When the surfactant is a sultaine or a salt thereof, it
preferably has the general formula:
RCONH(CH.sub.2).sub.mN.sup.+(CH.sub.3).sub.2CH.sub.2CH(OH)SO.sub.3.sup.-
[0032] wherein R is a hydrocarbon side chain, and m varies from
1-100.
[0033] In addition to the structures shown above, surfactants
having combinations of the various functional groups can also be
used. For example, an ethoxylated alkyl phenol also having a
sulphate group that would have a temperature stability and residue
characteristics suitable for the well being treated, could be used
with the method of the present invention.
[0034] Where, in the practice of the method of the present
invention, the surfactants function to create a foam, it is
sometimes desirable to break the foam after it is recovered from
the well. The term "breaking a foam", for the purposes of the
present invention, means to separate the gaseous component of the
foam from the liquid component. Any method known to be useful to
those of ordinary skill in the art of breaking foams such as those
sometimes formed in the practice present invention can be used with
the present invention, including both chemical and mechanical
methods.
EXAMPLES
[0035] The following examples are provided to illustrate the
present invention. The examples are not intended to limit the scope
of the present invention and they should not be so interpreted.
Amounts are in weight parts or weight percentages unless otherwise
indicated.
Example 1
[0036] In a gas lifted oil well in the Permian Basin subject to a
steady decline of liquid hydrocarbon production, the production
rate finally reaches no production. The average production rate for
the month prior to the loss of production is 18.1 barrels of
production per day (BOPD). The average production of oil per
million standard cubic feet (MMSCF) of lift gas during that period
is 0.175 BOPD/MMSCF of lift gas.
[0037] Production is resumed using an alkyl ether sulfate
surfactant available from Baker Petrolite under the trade
designation FMW3065. The surfactant is injected through the gas
lift valves at a rate of 3 gallons per day to increase the amount
of oil carried per unit of lift gas.
[0038] The rate of production after commencement of surfactant
injection is 21.8 BOPD. The average production of oil per MMSCF of
lift gas increases from 0.175 BOPD/MMSCF to 0.57 BOPD/MMSCF. The
lift gas compressor system runs noticeably smoother and required
less maintenance.
Example 2
[0039] Exemplary surfactants useful with the method of the present
invention are tested to determine whether they will leave a residue
on the gas lift system, potentially choking the system. This test,
known as the rack "gunking" test, is performed as follows.
[0040] Several milliliters of product are added to a watch glass,
which is then placed in a vacuum oven. The vacuum is increased
gradually to 75 cm Hg at a set temperature. (Temperatures are at
the highest temperature in the system. These can range from
100.degree. F. (38.degree. C.) to as high as 400.degree. F.
(204.degree. C.). After a specified amount of time that may vary
from 3 hours to 12 hours, the samples are removed and the watch
glass is tilted to an angle of approximately 45.degree.. The
tendency of the product to flow down the watch glass is recorded
over a temperature range with any signs of solids noted. The
results are recorded below in the Table.
1 TABLE Highest temperature at which surfactant has passed the rack
Product gunking test (.degree. F./.degree. C.). FMW25* 180/82
FMW35* 180/82 FMW3059* 140/60 FMW3053* 140/60 FMW3065* 77/25 *All
listed surfactants are available from Baker Petrolite under the
specified trade designations.
* * * * *