U.S. patent application number 14/354328 was filed with the patent office on 2014-11-20 for method and system for using tracer shots for estimating influx volumes of fluids from different influx zones to a production flow in a well.
This patent application is currently assigned to RESMAN AS. The applicant listed for this patent is Fridtjof Nyhavn. Invention is credited to Fridtjof Nyhavn.
Application Number | 20140343908 14/354328 |
Document ID | / |
Family ID | 45444709 |
Filed Date | 2014-11-20 |
United States Patent
Application |
20140343908 |
Kind Code |
A1 |
Nyhavn; Fridtjof |
November 20, 2014 |
METHOD AND SYSTEM FOR USING TRACER SHOTS FOR ESTIMATING INFLUX
VOLUMES OF FLUIDS FROM DIFFERENT INFLUX ZONES TO A PRODUCTION FLOW
IN A WELL
Abstract
A method for estimating influx volumes of fluids to a production
flow in a well with two or more influx locations along the well
includes arranging tracer sources with unique tracer materials in
fluid communication with two or more of the influx zones, each
tracer material having a predefined short duration release dose to
the fluids in the well, allowing the tracer sources to release the
tracer material to the fluids at a given release instant, after the
release instant, consecutively collecting samples of the production
flow at the topside, analysing the samples for identifying types of
tracer material and concentration of the identified tracer
materials, based on the concentrations and their sampling sequence
and the well geometry, sequence of the separate influx zones,
calculating the influx volumes from transient flow models using the
calculated influx volumes as parameters for controlling the
production flow or for characterizing the reservoir.
Inventors: |
Nyhavn; Fridtjof;
(Trondheim, NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nyhavn; Fridtjof |
Trondheim |
|
NO |
|
|
Assignee: |
RESMAN AS
Ranheim
NO
|
Family ID: |
45444709 |
Appl. No.: |
14/354328 |
Filed: |
October 28, 2011 |
PCT Filed: |
October 28, 2011 |
PCT NO: |
PCT/NO2011/000305 |
371 Date: |
May 6, 2014 |
Current U.S.
Class: |
703/2 |
Current CPC
Class: |
E21B 43/00 20130101;
E21B 47/11 20200501 |
Class at
Publication: |
703/2 |
International
Class: |
E21B 43/00 20060101
E21B043/00 |
Claims
1. A method for estimating influx volumes of fluids to a production
flow in a well with two or more influx locations along the well,
said method comprising the steps of: arranging tracer sources with
unique tracer materials in fluid communication with said influx
zones; each said tracer material having a predefined short duration
release dose to the fluids in the well; allowing said tracer
sources to release said tracer material to said fluids at a given
release instant; after said release instant, consecutively
collecting samples of said production flow at the topside;
analysing said samples for identifying types of tracer material and
concentration of said identified tracer materials; based on said
concentrations and their sampling sequence and the well geometry,
sequence of said separate influx zones, calculating said influx
volumes from transient tracer flow models; and using the calculated
influx volumes as parameters for controlling the production flow or
for characterizing the reservoir.
2. The method of claim 1, said tracer sources arranged for
releasing preferably simultaneously at a given release instant in
time.
3. The method of claim 1, wherein said release dose is released
during less than one minute.
4. The method according to claim 1, wherein said given release
instant being an advance determined instant in time.
5. The method according to claim 4, said given release instant
being one of a series of release instants, all predetermined before
assembly and installation of the production pipe assembly.
6. The method according to claim 1, said given release instant
being commanded from the surface.
7. The method according to claim 1, said two or more influx
locations being separate, influx locations mutually isolated in the
annulus around the production pipe.
8. The method according to claim 1, said tracer sources arranged in
fluid communication with said influx zones.
9. The method according to claim 1, said influx locations having
known positions along the well.
10. The method according to claim 1, after said release instant,
sampling after a time reasonably comparable to the minimum transit
time for a first of the tracers to reach the sampling site.
11. The method according to claim 1, further comprising the step of
collecting said consecutive samples of said production flow at the
topside at sampling times, said sampling sequence being sampling
times.
12. The method according to claim 1, further comprising the step of
collecting said consecutive samples of said production flow at the
topside at consecutive cumulative production volumes, said sampling
sequence being cumulative production volumes.
13. The method according to claim 1, the well geometry comprising
the sequence and positions of said separate influx zones, and the
length and geometry of the production pipe from the influx zones to
the topside.
14. The method according to claim 1, said production flow being in
a general steady state.
15. The method according to claim 1, said production flow a
ramp-up.
16. A system for estimating influx volumes of fluids to a
production flow in a well with two or more influx locations along
the well, comprising: tracer sources with unique tracer materials
arranged in fluid communication with said influx zones; each said
tracer material having a predefined short duration release dose to
the fluids in the well; said tracer sources provided with a timer
to release said tracer material to said fluids at a given release
instant; a sampling device for consecutively collecting samples of
said production flow at the topside after said release instant; an
analysing apparatus for said samples for identifying types of
tracer material and concentration of said identified tracer
materials; an algorithm for calculating said influx volumes from
transient tracer flow models based on said concentrations and their
sampling sequence and the well geometry, sequence of said separate
influx zones; and said calculated influx volumes for being used as
parameters for controlling the production flow or for
characterizing the reservoir.
17. The system of claim 16, said tracer sources arranged for
releasing preferably simultaneously at a given release instant in
time.
18. The system of claim 17, wherein said release dose is arranged
for being released during less than one minute.
19. The system according to claim 16, wherein said given release
instant is an advance determined instant in time.
20. The system according to claim 16, said given release instant
being one of a series of release instants.
21. The system according to claim 16, said given release instant
arranged for being commanded from the surface.
22. The system according to claim 16, said two or more influx
locations being separate, influx locations mutually isolated in the
annulus around the production pipe.
23. The system according to claim 16, said tracer sources arranged
in fluid communication with said influx zones.
24. The system according to claim 16, the well geometry comprising
the sequence and positions of said separate influx zones, and the
length and geometry of the production pipe from the influx zones to
the topside.
25. The system according to claim 16, the production tubing
comprising a sub with one or more breakable tracer
material-containing ampoules arranged to be broken individually by
one or more mechanical devices triggered by a timer unit arranged
in said sub, said sub provided with an electrical battery, each
said breakable ampoule provided with a discharge channel to the
fluid.
26. The system according to claim 25, said discharge channel
leading to the central production pipe.
27. The system according to claim 26, said discharge channel
leading to the annulus space outside the central production pipe,
said annulus space provided with holes to said central production
pipe, so as for said annulus space to form a delay chamber for
released tracer material.
Description
PATENT APPLICATION
[0001] To be filed as a PCT patent application on Oct. 28, 2011
without any preceding application
PRIOR ART
[0002] Resman has a patent on a specific method and device for
installing a polymer carrier for a chemical tracer material wherein
the polymer carrier is formed as thin rods placed in a cavity
within the well completion tubing outside the central tube. Such a
polymer carrier is arranged for long-time release of the tracer
materials and is not desirable to use in the present method, as it
is an advantage to have a "clean shot" release of the chemical
tracer material. However, the experience gained with tracer
flowback from more than 50 wells with such polymer carriers has
been a necessary basic for this new invention.
PROBLEMS RELATED TO THE PRIOR ART
[0003] The tracer carriers illustrated in FIG. 4 may be polymer
carriers with long-term release of tracer material. Annular wetting
is fluids from the annular space entering through a screen, wetting
the tracer carrier, and leaving to the annular space without local
passage to the central production tube. Tubing wetting is fluid
arriving through central pipe and deviating through a screen in the
tubing out to a closed sub enveloping a tracer carrier, and
returning with tracer material back through the internal screen to
the production tubing. Combined wetting may be obtained using a sub
with a screen for allowing influx from the annulus space and also
allowing passage through a screen from and to the central
production pipe, with a tracer carrier arranged between the central
tubing screen and the annulus screen.
[0004] In the present invention a downhole tracer release rate
changes, preferably in short pulses, while the well flow rate is
constant over time (or where the well flow rate changes slowly
relative to the short pulses of tracer release. Mechanical tracer
release chambers may be the source of such. If several chambers
release synchronously in a well the situation may be good as a
basis for extracting downhole inflow profile. This may correspond
to the situation of FIG. 1.2, with a mechanically or otherwise
controlled instantaneously released tracer at a given point of
time. This may prove advantageous if the different influx zones
have different influx pressures. If different influx pressures
exist, it is not feasible to create the "shots" illustrated in
FIGS. 1.2 and 1.3 by shutting in the well because cross-flow
between the zones may arise during shut-in.
[0005] There may be 20 to 30 influx zones in a well. The trend in
the technical field is that the number of influx zones is
increasing, and that one may arrive at 50 or more separate influx
zones. The reason for this increase in influx zones is due to
longer drilled production wells and using generally horizontally
drilled portions of the well, and exploitation of more complex
reservoirs.
[0006] According to an embodiment of the invention one may utilize
mechanically released so-called tracer shots. Groups of distinct
tracer materials are released in selected influx zones e.g. 4
different tracers at a time fired in each their separate zone. Then
one may calculate an image of the relative influx rates based on
sampling of a well flow which may have arisen such as illustrated
in FIG. 1. The total flux is expected to be measured topside.
Subsequently the same set of tracers, or a different set of
tracers, may be fired from other positions in the well at a later
time. This results in that one may do with a reduced number of
unique tracers than the number of influx zones. One may use tracer
release mechanisms which are installed in the production zone e.g.
during the completion of the well. It may be inappropriate or
impossible to set down tracer when the production has been started,
e.g. in subsea-wells wherein intervention is highly restricted due
to price or lack of access.
[0007] Another advantage using mechanical release according to the
invention is that it may take place at a desired point of time at a
desired place in the well. The installation of the completion may
take several days. A polymer carrier will usually start releasing
tracer immediately when in contact with the well fluids, and tracer
will be smeared out along the entire well during the completion
installation.
[0008] Problems related to long term release in this context [0009]
no sharp pulse. [0010] shut-in of the production required [0011]
cross flow between zones in case of non-steady state production
flow.
BRIEF SUMMARY OF THE INVENTION
[0012] The invention is a method for estimating influx volumes
(q.sub.i) of fluids to a production flow (F) in a well (W.sub.r)
with two or more influx locations (3) along the well [0013]
arranging tracer sources (4) with distinct tracer materials
(4.sub.m) in fluid communication with said influx zones (3), [0014]
each said tracer material (4.sub.m) having a well'defined,
comparatively short duration release dose (V.sub.t4) to the fluids
in the well, [0015] allowing said tracer sources (4) to release
said tracer material (4.sub.m) to said fluids at a given release
instant (t.sub.R), [0016] after said release instant (t.sub.R),
consecutively collecting samples (c.sub.1, c.sub.2, c.sub.3, . . .
) of said production flow (F) at the topside, [0017] analysing said
samples (c.sub.1, c.sub.2, c.sub.3, . . . ) for identifying types
of tracer material (4.sub.m) and concentration of said identified
tracer materials (4.sub.c), [0018] based on said concentrations
(4.sub.c, 41.sub.c, 42.sub.c, 43.sub.c) and their sampling sequence
and the well geometry, sequence of said separate influx zones,
calculating said influx volumes (q.sub.i) from transient tracer
flow models [0019] using the calculated influx volumes (q.sub.i) as
parameters for controlling the production flow or for
characterizing the reservoir.
[0020] The invention may also be defined as a system for estimating
influx volumes (q.sub.i) of fluids to a production flow (F) in a
well (W.sub.r) with two or more influx locations (3) along the
well, comprising [0021] tracer sources (4) with unique tracer
materials (4.sub.m) arranged in fluid communication with said
influx zones (3), [0022] each said tracer material (4.sub.m) having
a predefined short duration release dose (V.sub.t4) to the fluids
in the well, [0023] said tracer sources (4) provided with a timer
to release said tracer material (4.sub.m) to said fluids at a given
release instant (t.sub.R), [0024] a sampling device for
consecutively collecting samples (c.sub.1, c.sub.2, c.sub.3, . . .
) of said production flow (F) at the topside after said release
instant (t.sub.R), [0025] an analysing apparatus for said samples
(c.sub.1, c.sub.2, c.sub.3, . . . ) for identifying types of tracer
material (4.sub.m) and concentration of said identified tracer
materials (4.sub.c), [0026] an algorithm for calculating said
influx volumes (q.sub.i) from transient tracer flow models based on
said concentrations (4.sub.c, 41.sub.c, 42.sub.c, 43.sub.c) and
their sampling sequence and the well geometry, sequence of said
separate influx zones, [0027] said calculated influx volumes
(q.sub.i) for being used as parameters for controlling the
production flow or for characterizing the reservoir.
[0028] Advantageous embodiments of the invention are given in the
dependent claims.
ADVANTAGES OF THE INVENTION
[0029] An advantage of the invention over prior art is that as the
chemical tracer according to the invention is released over a short
period of time compared to the characteristic time constants of the
physics to be monitored or the physics to be exploited during the
monitoring process. The tracer is released over a short period
generally less than one minute and in practice probably in about 10
seconds. The tracer may advantageously be released under steady
state flow of the fluids in the well, and thus the method of the
invention incurs no or little disturbance to the well flow and that
information extraction may be done during relevant operating rate
condition. Thereby it is easier to understand details of the well
flow such as estimating the differences between different influx
zones' contribution to the total flow. If the calculation of the
different contributions to the well flow differ from what is a
desired flow pattern in the well, the operator may use the
calculated contributions from each influx zones as one of several
parameters for determining adjustments to the control of the
well.
FIGURE CAPTIONS
[0030] Embodiments of the method and device of the invention is
illustrated in the attached drawings, wherein
[0031] FIG. 1 shows a series of diagrams to visualize how the
tracer concentrations shots can be introduced in the production
stream and how the shots change as they are transported across the
reservoir interval. The downstream piping system and well path to
the topside equipment is not illustrated.
[0032] Nine frames are shown, FIGS. 1-1 to 1-9 illustrating the
technique. Each frame is a time step and describe how the tracer
shots move after being built up as a result of a tracer shot. The
diagrams represents a horizontal well with four tracers of
generally instant release, installed at positions labelled A, B, C,
D. For simplicity in this example the distances between each
subsequent tracer position along the wellbore are equal.
[0033] The tracer release devices are exposed to the well fluids
either from the outside of the completion or inside depending on
the carrier system. The tracers are released to the fluids at a
given instant. When released as illustrated in FIG. 1-2, then the
fluids immediately surrounding the tracer develop a high
concentration of the tracer. Such volumes are referred to as a
"tracer shot" and typically start off as equal volumes.
[0034] In FIG. 1-3 the well influx has started and each vertical
arrow in this example represent a given flow for example 1000 bopd
(barrels of oil per day).
[0035] As seen the influx from the zone between tracer C and D is
three times higher than the influx between zone A and B.
[0036] When the tracer slugs start moving with the well fluids as
seen in FIG. 1-5 these variations in influx between the zones will
affect the volume of fluids between each tracer slug and the
concentration of each slug as they pass across the zones.
[0037] The volume and hence time difference between the arrival of
slug C and D will be longer than between A and B due to the fact
that there will be three times more wellbore fluids that are
entering in between the two tracer slugs C and D. This is visually
represented in the FIGS. 1-6, 1-7, 1-8 and 1-9. Also the
concentration of tracer slug D will become more diluted and spread
out as a result of this higher influx, this is also visualized in
FIGS. 1-6 to 1-9.
[0038] FIG. 2 is an idealised illustration of concentration of
identified tracers sampled topside, with time or cumulative
production volume (since the injection) as the abscissa.
[0039] FIG. 3 is an illustration of an approach for matching the
unknown downhole influx rates in the downhole production zones with
the modelled influx rates. The model influx rates are adjusted
until the calculated concentrations of model tracers compare well
with the measured concentrations of identified tracers.
[0040] FIG. 4 gives a few rough examples of well fluids wetting
tracers generally according to prior art.
[0041] FIG. 5a is a simplified section through a petroleum well.
Influx volumes of fluids enters from the reservoir rocks to end up
in a production flow in a central production pipe in the well
provided with two or more separate influx locations. In this
situation the influx zones may not be precisely known and it is not
taken for granted that the tracers are placed where the influx
exactly occurs.
[0042] FIG. 5b is a simplified section through a petroleum well
wherein packers are arranged for mutually isolating the influx
zones. In this situation the tracers are also placed each in its
separate influx zone. There may be many more influx zones and
tracer carriers than what is illustrated in FIGS. 5a and b.
[0043] FIG. 6 comprises illustrations of embodiments of the
invention. In this example, the injection of the tracer shot
performed during steady-state flow so only the tracer forms a
transient in time, and the fluids with the tracer is eventually
flushed out from the isolated zone's completion void.
[0044] FIG. 6a illustrates one insulated influx zone insulated by a
lower (right) and an upper (left) packer defining a zone of influx
of petroleum fluids (and/or water) entering the annulus about the
production tubing, the fluids passing a mechanical tracer release
sub, (not yet released) and the fluids with more or less tracer
material leaving the annulus space through apertures in the central
production tube to the production flow which passes towards the
topside. A steady state flow rate is advantageous.
[0045] FIG. 6b illustrates the same setup, now with the mechanical
tracer release triggered and tracer material released into the
annulus space. A tracer shot of short temporal duration is created.
The dispersion of the tracer material will be a function of
turbulence and flow geometry in the annulus space.
[0046] FIG. 6c illustrates the subsequent step wherein the fluids
with the tracer shot with a more or less distributed tracer
material is flushed out the annulus space through apertures in the
central production tube to the production flow which passes towards
the topside. Again, a steady state flow rate is advantageous.
[0047] FIG. 7 shows curves of tracer shot release into the base
pipe from the annulus void of FIG. 6c into the central production
pipe (base pipe) as a function of time. The "rate 2Q" curve
indicates a twice as high influx rate as the "rate Q" curve, both
washing out the same amounts of tracer delivered by equal shots.
Please notice that the area under the 2Q and Q rate curves are
equal. Please also notice that both curves approach nil
concentration as the doses released are finite at the short term.
The higher rate will flush out fastest and die out faster, while
the lower influx rate will wash out at a lower rate and sustain at
a detectable level for longer.
[0048] FIG. 8 comprises illustrations of a possible problem. In
this situation the tracer shot is built over time from the tracer
leak-out from polymers into still shut-in fluids. The flow-back of
the shot to surface is then done during production ramp-up. In this
example, not only the tracer forms a transient in time, but there
may also occur a cross-flow of fluid from the shown zone to another
zone during the build-up of the shot, which will complicate the
backflow pattern and obscur the measurements obtained.
[0049] FIG. 8a illustrates a situation similar to what is
illustrated in FIG. 6a, with the difference that tracer is released
more or less at a constant rate over long time, e.g. tracers from a
polymer rod arranged in the annular space outside the central
production tube. The fluid carries tracer with it at a generally
even rate with the production flow.
[0050] FIG. 8b illustrates the result of a shut-in downstream
(topside) in order to build a concentration in the annulus space,
called to build a "shot". This method may work well in case there
is no cross flow, but the method of using a continuous release of
tracer is sensitive to crossflow between zones (this is one zone)
through the central production pipe, if a downstream (topside)
shut-in is used. If the shut-in occurs downhole between all influx
zones and the production pipe, this is not a problem, but requires
a more elaborate well control apparatus.
[0051] FIG. 8c illustrates that the tracer concentrated fluid (the
"shot") is flushed out with resumption of the production by opening
the topside valve, and the partially leaked-out shot will be
flushed out as a longer pulse than strictly desirable because of
the potentially non-ideal build-up of the shot.
[0052] FIG. 9 shows ideal curves of tracer shot release into the
base pipe from the annulus void of FIG. 6c into the central
production pipe (base pipe) as a function of time, in the situation
described for FIG. 8c, but without cross-flow, i.e. it is the best
imaginable situation of shut-in with long term release of tracer.
Please notice that both curves cannot approach nil concentration as
the doses are continually released. The higher rate will flush out
fastest and die out faster, while the lower influx rate will wash
out at a lower rate, but both may be at a detectable level for very
long time.
[0053] FIG. 10 illustrates a mechanical tracer release sub
according to an aspect of the invention and for use with the method
according to the invention. A tracer dose is in this case arranged
in a breakable ampoule, e.g. in a glass bulb and to release through
holes open to the central production pipe. A release mechanism
comprising such as a small explosive charge or a puncturing needle
is arranged for breaking the breakable ampoule controlled by a
timer of an electronic unit. The electronic unit, please see
section B-B, is preferably provided its own electric battery and is
preferably arranged to trigger the release mechanism at a given
date and time of day. There may be arranged a series of such
breakable ampoules around the perimeter of the release sub, please
see section A-A, in order for enabling a series of measurement
rounds over time, each ampoule predestined to break at long
intervals, such as one each month, each six months, or more. The
entire release sub may be provided with end rings such as friction
slip rings for being mounted into the central production tubing and
inserted with the completion into the production zone. The setup in
FIG. 10 will typically be used in the context described in FIG. 1
where venting towards the central base pipe is needed.
[0054] FIG. 11 shows a similar embodiment of the mechanical tracer
release sub according to a slightly different embodiment of the
invention, for use with the method according to the invention. The
tracer doses are arranged in breakable ampoules which are arranged
with vent holes of the sub open to the annulus space and not to the
production pipe directly. Otherwise the mechanical release sub is
similar to what is described under FIG. 10. This mechanical
embodiment thus releases into the void outside the central
production pipe and should be used in the context shown in FIG. 6
with flush-out from the insulated zone in the annulus void in the
completion, and will work along the lines of FIG. 7.
[0055] FIG. 12 illustrates this mechanical embodiment which
releases into the void outside the central production pipe and used
in the context shown in FIG. 6 with flush-out from the insulated
zone in the annulus void in the completion.
[0056] FIG. 13 relates to a setup with tracer shots being injected
into the central base pipe, as also explained in FIG. 1. FIG. 13
shows curves of tracer concentrations as function of cumulative
production volume topside. In the upper portion of the drawing
there is illustrated highly simplified illustrations of two
parallel production zones called "zone 1" and "zone 1 &
5"(which may produce into the same main well) or two wells on the
same tie-back, leading to the same topsides sampling site. The
vertical coloured lines are the positions of tracers in insulated
influx zones to the two branches. The different coloured lines in
the curves indicate measured concentrations (interpolated). The
vertical bars of same colours indicate peak arrivals (as function
of cumulative volume) if even influx rates had existed and this is
calculated from models. One will see that the first (heel)
production of zone 1 and zone 1 & 5 arrive almost as predicted
from the even rate model, but that the toe marker of zone 1 arrives
far too early and its influx must be higher than presumed, and the
nearer toe of zone 1 & 5 arrives far too late and must be due
to a lower influx than presumed. This indicates that the influx
model should be adjusted significantly.
[0057] FIG. 14 shows the same measured curves and well models as
for FIG. 13 above. A general scheme of comparison between the Real
World and the model world as shown in FIG. 3 may be used. The
difference is that here the influx model of "zone 1" and "zone 1
& 5" are heavily corrected to indicate influx rates downhole
"zone 1" of 18%, only 1%, and as high as 43% contributions to the
combined total flow topside, and for zone 1 & 5 contributions
of 9% at the heel, 10%, and 18% at the toe. Here we see that the
middle production zone of "zone 1" contributes insignificantly and
may be shut down or considered as a candidate for an overhaul. One
will now see that the predicted peak arrivals coincide with the
actual peaks.
[0058] As an improvement, further curve analysis could be conducted
in order to determine the assumed continuous curve peak arrivals
from the non-continuous measurement results, as the peak of a
non-continuous series is not necessarily the real peak. Anyway, the
illustrated match is far better than for FIG. 13.
Embodiments of the Invention
[0059] The invention is a method for estimating influx volumes
(q.sub.i) of fluids to a production flow (F) in a well (W.sub.r),
please see FIG. 5. The well is provided with two or more separate
influx locations (3, 31, 32, 33) along the well. The actual
positions of the influx locations are not necessarily precisely
known. Tracer sources (4, 41, 42, 43) with distinct tracer
materials (4m, 41m, 42m, 43m) are arranged upstream/downstream said
influx zones (3, 31, 32, 33). Each said tracer material (4.sub.m)
has a predefined, comparatively short, quickly released dose
(V.sub.t4) (short release time dose) to the fluids in the well.
[0060] With the term "comparatively short" we here mean
significantly short compared to subsequent sampling intervals,
compared to the time required for the well flow's transit time from
the influx zones to the topside of the well, compared to possibly
the leak-out time constant from the annulus to the central
production pipe if the tracer is released into an external void in
the well completion and compared to the characteristic time
constant of the physics we are monitoring. The influx zone furthest
from the topside is called the "toe" and the nearest influx zone is
called the "heel". The method aims at extracting information from
tracer transients in the petroleum fluid (or water) flowback of
tracers to the surface.
[0061] The tracer sources (4, 41, 42, 43) are according to the
invention allowed to release the tracer material (4m, 41m, 42m,
43m) to the fluids each belonging zone at a given release instant
(t.sub.R). The tracer sources according to the invention are
arranged to release the tracers at a given instant in time in order
for the subsequent topsides sampling to be conducted rationally. In
an embodiment of the invention this is done by providing each
tracer source downhole with a timer which is set for triggering the
release at a given date and time. The release may be repeated at
one or more later given date and time in order to conduct further
measurement series.
[0062] After the release instant (t.sub.R), samples (c.sub.1,
c.sub.2, c.sub.3, . . . ) of the production flow (F) are
consecutively collected at the topside. The sampling may simply be
conducted by tapping small amounts of the petroleum flow (F) at
registered times. An alternative to sampling as a function of time
is to collect sample at intervals based on cumulative petroleum
volumes (f.sub.1, f.sub.2, f.sub.3, f.sub.4), if the flow is not a
steady-state flow. (One may collect samples at regular time
intervals and plot and analyze the measurements as a function of
cumulative productin.)
[0063] After sampling, the samples (c.sub.1, c.sub.2, c.sub.3, . .
. ) are analysed for identifying the types of one or more tracer
material (4m, 41m, 42m, 43m) and their corresponding concentrations
(4c, 41c, 42c, 43c) of the identified tracer materials.
[0064] In an embodiment of the invention the analysis is conducted
on site during the sampling period using field analysis instruments
topside in order to provide results rapidly. The analysis may be
conducted in a chemical laboratory in order to provide more precise
measurements or for verifying or refining field measurements.
[0065] Rough Calculation
[0066] Based on the measured concentrations (4.sub.c, 41.sub.c,
42.sub.c, 43.sub.c) and their sampling sequence, i.e. sampling
times or cumulative production volumes (f.sub.1, f.sub.2, f.sub.3,
f.sub.4) and the well geometry, one may calculate the influx
volumes (q.sub.i) from transient tracer flow models (in a
preferably, but not necessarily steady state flow). The well
geometry comprises the sequence and positions of the separate
influx zones, and the length and geometry such as pipe diameters
corresponding lengths of the sections of production pipe, possibly
including tie-back pipes, all the way from the influx zones to the
topside sampling point.
[0067] Utilizing Calculated Influx Volumes
[0068] The calculated influx volumes (q.sub.i) are used as
parameters for comparison indirectly with the real measurements so
as for controlling changes to the production flow, such as
increasing or decreasing the total flow topside or adjusting the
influx from the separate influx zones using valves between the
influx zones and the central production pipe, or adjusting the flux
ratios from well branches' production pipes into a main well.
[0069] Refining the Calculations
[0070] A model of the well may be established. The model may be
adjusted with regard to influx volumes in the distinct zones until
there is correspondence in the measured concentration curves and
the modeled calculation curves.
[0071] Decisions Based on Many Parameters
[0072] The well operator will usually not decide on controlling the
well flow only based on the estimates of influx volumes, but use
additional relevant parameters such as pressure and fluid
composition and other operational parameters.
[0073] Simultaneous Release All or in Groups
[0074] In an advantageous embodiment of the invention each tracer
source (4) arranged for releasing preferably simultaneously, at
least in groups, at a given release instant (t.sub.R) in time. One
may release in all influx zones in the well simultaneously if so
many different tracers are available. If the number of influx zones
in the well is high, say 30 to 50 or more, one may release a
limited number of different tracers, say 4 to 6, in a corresponding
number of isolated influx zones at a time, and repeat the release
with the same set of tracers in subsequent sets of zones with a
required sufficient delay until the entire well is covered.
[0075] Release Duration
[0076] In an advantageous embodiment of the invention, the release
dose (V.sub.t4) is released during less than one minute, preferably
less than 10 seconds. The release time rather short so that the
release of tracer is a pulse compared with characteristic time
constants of the flow events that we are monitoring, and, in case
we have a delay chamber, significantly shorter than the
characteristic time constant of the delay chamber.
[0077] Release Instant Control
[0078] In an advantageous embodiment of the invention, the given
release instant (t.sub.R) is an advance determined instant in time.
The release instant may be set while installing the mechanical
release sub in the completion, before the entire completion is
inserted into the well production zone. The mechanical release sub
may be provided with a self-powered timer in a tracer release unit
so as for to avoid any external power supply, and also for avoiding
control lines from the surface: one knows the date and time the
tracers are released, and sampling must be conducted in a required
number of samples through a sufficiently long time after the
release, and one will have a good set of samples to analyze.
[0079] The given release instant (t.sub.R) may be being one of a
series of release instants. In an advantageous embodiment of the
invention all the release instants may be predetermined before
assembly and installation of the production pipe assembly. Thus one
may conduct a release of tracers, sampling and analysis according
to the invention short after the start-up of production or test
production in a well, and then conduct another round of release,
sampling and analysis after one month, after two months, and so on
for a long time, and obtain improved control over the well.
[0080] In an embodiment of the method of the invention the given
release instant (t.sub.R) may be commanded from the surface. A
signal transmitter at the topside may be arranged to send a
"request to release" signal to the sub containing a corresponding
signal receiver in the mechanical tracer dose release unit of the
invention. In an embodiment, the actual tracer release point of
time may still be set in the electronic control module in the sub
to be delayed to a predefined hour, minute and second, so one may
be certain that the tracer is released at an exactly known point in
time.
[0081] In an advantageous embodiment of the invention, the method
is conducted in a well wherein the two or more influx locations are
separated by e.g. packers, so as for the influx locations to be
mutually isolated in the annulus around the production pipe. In
this way one may be sure that there is no mixing of the
contributions from the different influx zones before the fluids
enter the central pipe, and one may expect the samples topsides to
be better for distinguishing the different influx zones. In such a
model the dispersion of the tracer materials will be dominated by
the physical conditions and geometry of the well above the influx
zones on the fluids' way to the sampling site topside.
[0082] In an advantageous embodiment of the invention the tracer
sources are arranged in fluid communication with the influx zones.
More specifically, the tracer sources are preferably, if possible,
each arranged within or very near its corresponding influx zone so
as to have a relatively short flux path from the influx zone, past
the tracer source, and out through vents to the production pipe,
such as illustrated particularly in FIG. 8 and FIG. 12.
[0083] In an embodiment of the invention one may have knowledge of
the influx locations' (3) positions along the well from well logs.
This may improve the certainty of the modelling of the tracers'
propagation to the surface. Alternatively, the real positions are
unknown, but may be varied in the model well in order to better
match the modelled tracer arrivals topside.
[0084] In and embodiment of the method of the invention, the
sampling is conducted after said predefined release instant
(t.sub.R), after a time reasonably comparable to the minimum
transit time for a first of the tracers to reach the sampling site.
This is in order to avoid starting sampling before the first tracer
may actually arrive through e.g. the tie-back length of several
kilometres of pipe to the topside location.
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