U.S. patent application number 10/312246 was filed with the patent office on 2003-09-11 for method and system for stepwisevarying fluid flow in well.
Invention is credited to Bergren, Frank Edward.
Application Number | 20030168223 10/312246 |
Document ID | / |
Family ID | 29585618 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030168223 |
Kind Code |
A1 |
Bergren, Frank Edward |
September 11, 2003 |
Method and system for stepwisevarying fluid flow in well
Abstract
A method for stepwise varying fluid flow in a well utilizes a
plurality of downhole valves which have orifices of different sizes
in the valve bodies, so that fluid flow can be varied by partially
closing one or more valves. The method may be used for testing gas
wells such that the wellbore storage delays caused by gas
compression and/or expansion in the production tubing are
minimized.
Inventors: |
Bergren, Frank Edward;
(Rijswijk, NL) |
Correspondence
Address: |
Richard F Lemuth
Shell Oil Company
Intellectual Property
PO Box 2463
Houston
TX
77252-2463
US
|
Family ID: |
29585618 |
Appl. No.: |
10/312246 |
Filed: |
December 23, 2002 |
PCT Filed: |
July 3, 2001 |
PCT NO: |
PCT/EP01/07629 |
Current U.S.
Class: |
166/386 ;
166/332.3 |
Current CPC
Class: |
E21B 34/06 20130101;
E21B 2200/04 20200501 |
Class at
Publication: |
166/386 ;
166/332.3 |
International
Class: |
E21B 033/12 |
Claims
1. A method for stepwise varying fluid flow in a well by means of a
downhole valve assembly that can be switched between a first
position in which fluid flow is permitted and a second position in
which fluid flow is inhibited, wherein the valve assembly comprises
a plurality of valves which each comprise an orifice through which
a limited flow of fluid is allowed when the valve is in the second
position thereof.
2. The method of claim 1, wherein the valves comprise orifices that
form different flow restrictions and wherein the method is used to
determine the properties of the rate-dependent skin around the
inflow region of a gas production well and wherein during a
selected period of time a first valve is in the second position and
each of the valves are in the first position thereof, which period
is followed by another selected period of time during which a
second valve is in the second position and each of the other valves
is in the first position thereof.
3. The method of claim 2, wherein the valve assembly comprises at
least three valves and wherein during a first period of time a
first valve, which has an orifice that forms a larger flow
restriction than the other valves is maintained in the second
position and the other valves are in the first position thereof,
which period of time is followed by a second period during which a
second valve which has an orifice that forms a smaller flow
restriction than the first valve, but larger flow restriction than
the other valve or valves, is in the second position and the other
valves are in the first position and which second period of time is
followed by a third period of time during which a third valve which
has an orifice that forms a smaller flow restriction than the
orifices of the first and second valves is in the second position
and the first and second valves are in the first position.
4. The method of claim 3, wherein said first, second and third
periods of time have a substantially equal duration which is
between 0.5 and 50 hours.
5. The method of claim 4, wherein said duration is between 1 and 20
hours.
6. A system for stepwise varying fluid flow in a well, the system
comprising a downhole valve assembly that can be switched between a
first position in which fluid flow is permitted and a second
position in which fluid flow is inhibited, wherein the valve
assembly comprises a plurality of valves which each comprise an
orifice through which a limited flow of fluid is allowed when the
valve is in the second position thereof.
7. The system of claim 6, wherein the valves are mounted on a
common carrier body which can be lowered into the well through the
production tubing and which is provided with a shoulder that can be
landed in a nipple to seal off an annular space between carrier
body and the tubing.
8. The system of claim 7, wherein the valves have openings in which
valve bodies are rotatably arranged, which openings form a
longitudinal fluid passageway through the centre of the carrier
body.
9. The system of claim 8, wherein the valves are ball valves having
each a first orifice and a second orifice which is oriented in a
direction orthogonal to the first orifice and which is smaller than
the first orifice.
10. The system of claim 9, wherein the carrier body carries at
least four valves which each have a second orifice that forms a
flow restriction different from the flow restrictions formed by the
second orifices of the other valves.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method and system for stepwise
varying fluid flow in a well.
[0002] Generally fluid flow in a well is controlled by a production
choke at the wellhead whereas downhole safety valves and/or test
valves are installed which generally can be switched between a
fully open and a fully closed position.
[0003] Such dual position downhole valves can be actuated by spring
mechanisms that can be triggered by acoustic or hydraulic pulses so
that they do not require a wear prone electric motor and electrical
power supply and control conduits, which are difficult to install
and remove, in particular in a complex multilateral well.
[0004] Currently gas wells are tested by flowing the well at three
or four different flow rates and calculating the so-called total
skin at each flowrate. Said total skin is an accumulation of the
mechanical skin (permeability reduction due to mud invasion,
partial penetration effects and other relatively constant factors)
and the rate-dependant (or non-Darcy) skin (which is due to
turbulence or non-Darcy flow effects).
[0005] From the flowrate data gathered the well test procedure the
total skin is plotted as a function of flow rate and the rate
dependant skin is calculated as the slope of a line fit through the
data.
[0006] In this procedure, each flow period must reach either Pseudo
Steady State (PSS) which is known as "stabilized" flow in the gas
well testing literature of the 1950's through the 1970's, or
Infinite Acting Radial Flow (IARF). Because the time required to
reach IARF is much shorter than the time required to reach PSS, the
most economic method is to flow the well until sufficient IARF data
has been gathered, and then change the rate to the next flow rate
in the test program.
[0007] Details of gas well test procedures at different flow rates
to determine the effect of the mechanical and rate dependant skin
are disclosed in the handbook "Modern Well Test Analysis, A
Computer Aided Approach", Second Edition; author R N Horne, issued
in 1995 by Petroway, Inc.
[0008] If the rate change from one flow rate to the next is imposed
by the production choke valve at the surface, the high
compressibility of the gas and the large volume of tubing between
the Total Depth (TD) of the well and the surface choke results in a
long "wellbore storage" or "after flow" period prior to the IARF
period. In order to reduce the wellbore storage period downhole
test valves exist to achieve pressure build-ups (in which the rate
is changed to a rate of zero) with minimal wellbore storage. These
test valves have been very successful and are widely used now.
[0009] Examples of these remotely actuable dual position test
valves are the electronic downhole shut-in tool marketed by
Halliburton Energy Services, Inc. under the tradename ETUX and the
IRIS (a Schlumberger trademark) dual-valve tool marketed by
Schlumberger Technical Services Inc. The IRIS dual-valve uses
annulus pressure levels to transmit signals from surface to switch
the valve between the open and closed position and the ETUX valve
incorporates a downhole computer to perform a pre-programmed test
procedure.
[0010] With these known downhole valve assemblies and variable
production choke it may still take significant time to reach IARF
and allow the production to stabilize before a next rate change can
be applied, in particular in deep wells and if skin effects are
high. In a typical 3000 m deep gas well the time required to reach
IARF could take 20 hours and the next rate change should not be
imposed until about 100 hours.
[0011] Therefore the well test procedures take significant amount
of time during which produced gas may be flared and significant
personnel and materials expenses are made, in particular if the gas
is produced offshore or in a remote area.
[0012] The present invention aims to alleviate these problems
associated with the prior art test methods and to provide a method
and system for stepwise varying fluid flow in a well such that the
time required for testing the well is reduced.
[0013] The present invention also aims to provide a method and
system for stepwise varying fluid flow in a well which can not only
be operated in well test procedures but which permanently or
temporarily operates downhole to adjust the flowrate from different
well branches into a main wellbore of a multilateral well.
SUMMARY OF THE INVENTION
[0014] In the method according to the invention fluid flow in a
well is varied stepwise by means of a downhole valve assembly that
can be switched between a first position in which fluid flow is
permitted and a second position in which fluid flow is inhibited,
wherein the valve assembly comprises a plurality of valves which
each comprise an orifice through which a limited flow of fluid is
allowed when the valve is in the second position thereof.
[0015] Preferably the valves comprise orifices that form different
flow restrictions and wherein the method is used to determine the
properties of the rate-dependent skin around the inflow region of a
gas production well and wherein during a selected period of time a
first valve is in the second position and each of the valves are in
the first position thereof, which period is followed by another
selected period of time during which a second valve is in the
second position and each of the other valves is in the first
position thereof.
[0016] In such case it is also preferred that the valve assembly
comprises at least three valves and wherein during a first period
of time a first valve, which has an orifice that forms a larger
flow restriction than the other valves is maintained in the second
position and the other valves are in the first position thereof,
which period of time is followed by a second period during which a
second valve which has an orifice that forms a smaller flow
restriction than the first valve, but larger flow restriction than
the other valve or valves, is in the second position and the other
valves are in the first position and which second period of time is
followed by a third period of time during which a third valve which
has an orifice that forms a smaller flow restriction than the
orifices of the first and second valves is in the second position
and the first and second valves are in the first position.
[0017] Generally said first, second and third periods of time have
a substantially similar duration which is sufficient to reach IARF.
For most gas reservoirs said duration will be in the range between
0.5 and 50 hours, and typically between 1 and 20 hours.
[0018] The invention also relates to a system for stepwise varying
fluid flow in a well. The system comprises a downhole valve
assembly that can be switched between a first position in which
fluid flow is permitted and a second position in which fluid flow
is inhibited, wherein the valve assembly comprises a plurality of
valves which each comprise an orifice through which a limited flow
of fluid is allowed when the valve is in the second position
thereof.
[0019] Preferably the valve assembly is retrievably mounted in a
production tubing such that the valves can be inserted into and
retrieved from the well through the interior of the tubing whilst
the production tubing remains in place. This can be accomplished by
mounting the valves on a common carrier body which can be lowered
into the well through the production tubing and which is provided
with a sealing ring assembly which can be landed in a nipple to
seal off an annular space between carrier body and the tubing.
[0020] It is observed that U.S. Pat. No. 5,447,201 discloses the
use of a permanently installed downhole valve, which can be
maintained in any partly open position, but such a valve is wear
prone and requires the use of electric or hydraulic power cables
which involves a complex and expensive well infrastructure. In the
method and system according to the present invention the downhole
chokes can be operated wireless, for example by using a
time-controlled or fluid pulse actuation mechanism, and be
installed inside an existing tubing using a slickline, which does
not comprise electric or hydraulic conduits.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The invention will be described in more detail, and by way
of example, with reference to the accompanying drawings, in
which:
[0022] FIG. 1 is a schematic representation of a valve assembly
according to the present invention at the bottom of a production
tubing inside a gas production well;
[0023] FIG. 2 shows schematically how the gas production rate is
influenced by sequentially positioning one of the four valves of
the assembly shown in FIG. 1 in its first, substantially closed,
position; and
[0024] FIG. 3 shows how with the valve assembly according to the
invention IARF can be reached within about 10 hours, whereas with a
conventional surface choke it would take up to about 100 hours to
reach IARF.
[0025] Referring to FIG. 1 there is shown the lower portion of a
gas production well 1, which traverses an underground gas bearing
formation 2.
[0026] The well 1 comprises a well casing 3, which is cemented
within the wellbore and which is equipped with a series of
perforations 4 through which gas enters the wellbore as is
illustrated by arrows 5. A production tubing 6 is suspended in the
well 1 and sealingly anchored near its lower end to the well casing
3 by a production packer 7. A valve assembly 8 comprising a set of
four ball valves 8A, 8B, 8C and 8D.
[0027] Each of the valves 8A-D is shown in the first, open,
position, wherein the central bores 9 in the valve bodies 10 are
aligned with each other and with a central bore 11 in a valve
carrier body 12.
[0028] The valve carrier body 12 is sealingly and removably secured
inside the production tubing 6 by landing a shoulder 13 in a nipple
and is suspended from a reeling drum at the wellhead (not shown) by
means of a wireline 14.
[0029] If desired the wireline 14 may be equipped with electrical
or fibre optical, power and/or communication conduits to power the
valve bodies 8A-8D. Alternatively the wireline 14 is only a
hoisting cable, cq. slickline, and the valve bodies are powered by
springs and/or a downhole electronic system which is powered by the
gas flow and/or a downhole electrical battery (not shown).
[0030] The valve bodies 10 are, apart from the central bore 9, also
equipped with orifices 15A-D, which intersect the central bore 9 of
the relevant valve body 10 in an orthogonal direction.
[0031] The orifices 15A-D have a cylindrical shape, the orifice 15A
of the uppermost valve 8A has the largest diameter, whereas the
orifice 15D of the lowermost valve 8D has the smallest diameter.
The orifice 15B of the valve 8B has a larger diameter than the
diameter of the orifices 15C and D of the valves 8C and 8D, but a
smaller diameter than the orifice 15A of the uppermost valve
8A.
[0032] When the gas well 1 is to be tested the valve assembly 8 is
lowered through the interior of the production tubing 6 by paying
out the wireline 14 until the valve assembly 8 is located close to
the lower end of the tubing 6. Then the valve assembly is sealingly
secured inside the production tubing 6 by landing the shoulder 13
in the nipple.
[0033] Then gas production is allowed to start by opening the
surface choke (not shown) at the wellhead whilst the valves 8A-D of
the valve assembly 8 are in the first, open, position as is
illustrated in FIG. 1.
[0034] Then during a first phase I of the well test cycle the
first, lowermost valve 8D is positioned in the second position
thereof, whilst the other valves are maintained in the first, open,
position.
[0035] As illustrated in FIG. 2 said first phase I continues for
about 10 hours, which is sufficient for the well 1 to reach IARF as
illustrated in FIG. 3.
[0036] The example is based on a computer simulation of the effects
of a downhole test choke assembly in which the following
assumptions were made:
1 h: 30 m = thickness of the gas bearing formation k: 1.0 md =
formation permeability S: 15 =skin .mu..sub.g: 0.0198 cp. = gas
viscosity C.sub.g: 4.2E.sup.-5 kPa.sup.-1 = gas compressibility
Tubing Diameter: 9 cm Well Depth: 3000 m Test Tool Depth: 2900
m
[0037] In the diagram shown in FIG. 2 it is assumed that the
diameter of the orifice 15A of the first valve is 3 cm and that the
diameters of the orifices 15B, 15C and 15D of the second, third and
fourth valves 8B, 8C and 8D are 2.5; 2 and 1.3 cm.
[0038] The diagram shown in FIG. 2 indicates that under the above
conditions the downhole pressure p.sub.I during the first phase I
increases and that the gas flow rate Q.sub.I decreases.
[0039] FIG. 3 shows that in the example shown as a result of the
pressure measurement with a pressure sensor at the wellhead and the
absence of a gas column with a length of 2900 m and a volume of
1/4..pi..0.09.sup.2.2900=18.4 m.sup.3 the response of the well 1
with a downhole choke as represented by pressure curve 20 is much
quicker than if the well production would be reduced with a surface
choke as represented by pressure curve 21 and that accordingly the
time required to reach IARF is reduced from 100 hours to 10
hours.
[0040] Referring again to FIGS. 1 and 2, when the well has reached
IARF after about 10 hours the second test phase II is commenced by
placing the fourth, lowermost valve 8D again in the first, open,
position and simultaneously placing the third valve 8C in the
second position whilst the first and second valves 8A and 8B are
maintained in their first, open, position.
[0041] The diameter of the orifice 15C is 2 cm, which is larger
than that of the fourth valve 8D so that during the second phase I
the downhole pressure P.sub.II decreases whereas the gas production
Q.sub.II increases.
[0042] When IARF is reached after about 10 hours the second test
phase II is terminated and the third test phase III is commenced by
placing the second valve 8B in the second position and placing the
other valves 8A, 8C and 8D in the first, open position.
[0043] Since the orifice 15B of the third valve BC is 2.5 cm, which
is larger than the diameters of the orifices of the third and
fourth valves 8C and D, the downhole pressure P.sub.III decreases,
whereas the gas production rate Q.sub.III further increases.
[0044] When IARF is reached again after about 10 hours the third
test phase III is terminated and the fourth test phase IV is
commenced by placing the first valve BA in the second position and
placing the second, third and fourth valves 8B, 8C and 8D in the
first, open, position.
[0045] Since the orifice 15D in the valve body 10 of the fourth
valve 8D is 3 cm, which is larger than the diameters of the
orifices 15A-D of the other valves 8A-C, the downhole pressure
P.sub.IV will further decrease, whereas the gas production rate
will further increase.
[0046] When IARF is again reached after about 10 hours the fourth
test phase IV is terminated and a downhole valve is closed so that
the gas flow Q.sub.o is interrupted and the pressure P.sub.o
increases until it reaches the reservoir pressure and then the
valve assembly 8 is retrieved to surface.
[0047] As can be seen in FIG. 2 the four phases I-IV of the total
well test cycle take in total about 40 hours.
[0048] If the well would have been equipped with a traditional
surface choke and a single downhole valve that would be closed to
achieve pressure build up when the position of the surface choke is
changed the total test cycle would have taken about 400 hours.
Thus, the test time is reduced by about 90% by using the valve
assembly 8 according to the invention.
* * * * *