AU2011380070A1 - Method and system for using tracer shots for estimating influx volumes of fluids from different influx zones to a production flow in a well - Google Patents

Abstract

A method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations (3) along the well - arranging tracer sources (4) with unique tracer materials (4m) in fluid communication with two or more of said influx zones (3), - each said tracer material (4m) having a predefined short duration release dose (Vt4) to the fluids in the well, - allowing said tracer sources (4) to release said tracer material (4m) to said fluids at a given release instant (tR), - after said release instant (tR), consecutively collecting samples (c1, c2, c3,...) of said production flow (F) at the topside, - analysing said samples (c1, c2, c3,...) for identifying types of tracer material (4m) and concentration of said identified tracer materials (4c), - based on said concentrations (4c, 41c, 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, calculating said influx volumes (qi) from transient flow models - using the calculated influx volumes (qi) as parameters for controlling the production flow or for characterizing the reservoir.

Description

WO 2013/062417 PCT/N02011/000305 Patert application To be filed as a PCT patent application on 28. 10201 without any preceding application 5 Title of the invention: Method and device for us ng tracer shots for estimating -influx volumes of fluids from different rifiuc zones to a production flow in a well. ) Inventor- Fridtjof Nyhavn Trondhe im Norway. n Resman AS Trondheim , PCT patent attorney ) Fluges patent as, P.O.Box 27 62 Gamle Fredrikstad . .orwa * - * - WO 2013/062417 PCT/N02011/000305 Prior art Resman has a patent on a specific method and device for installing a polymer carrier for a chemical tracer material wherein the polymer 5 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. 0 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. 5 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 0 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 5 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. 0 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 5 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 2 WO 2013/062417 PCT/N02011/000305 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 Fig. 1.2 and 1.3 by 5 shutting in the well because cross-flow between the zones may arise during shut-in. 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, 0 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. 5 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 D 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. 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 3 WO 2013/062417 PCT/N02011/000305 will be smeared out along the entire well during the completion installation. Problems related to long term release in this context 5 - no sharp pulse. - shut-in of the production required - cross flow between zones in case of non-steady state production flow. D Brief summary of the invention The invention is a method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations (3) along the well - arranging tracer sources (4) with distinct tracer materials (4m) in fluid communication with said influx zones (3), - each said tracer material (4m) having a well'defined, comparatively short duration release dose (V1 4 ) to the fluids in the well, - allowing said tracer sources (4) to release said tracer material (4m) to said fluids at a given release instant (tR), - after said release instant (t,), consecutively collecting samples (c 1 , c 2 , c 3 , ... ) of said production flow (F) at the topside, - analysing said samples (cI, c 2 , c 3 , ... ) for identifying types of tracer material (4m) and concentration of said identified tracer materials (4), - based on said concentrations (4c, 41c, 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, calculating said influx volumes (qi) from transient tracer flow models - using the calculated influx volumes (qi) as parameters for controlling the production flow or for characterizing the reservoir. The invention may also be defined as a system for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations (3) along the well, comprising 4 WO 2013/062417 PCT/N02011/000305 - tracer sources (4) with unique tracer materials (4m) arranged in fluid communication with said influx zones (3), - each said tracer material (4m) having a predefined short duration release dose (V 4 ) to the fluids in the well, 5 - said tracer sources (4) provided with a timer to release said tracer material (4m) to said fluids at a given release instant (tR) - a sampling device for consecutively collecting samples (c 1 , c 2 , c 3 , ... ) of said production flow (F) at the topside after said release instant (tR), 0 - an analysing apparatus for said samples (c 1 , c 2 , c 3 , ... ) for identifying types of tracer material (4m) and concentration of said identified tracer materials (4c), - an algorithm for calculating said influx volumes (qj) from transient tracer flow models based on said concentrations (4c, 41c, 5 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, - said calculated influx volumes (qi) for being used as parameters for controlling the production flow or for characterizing the reservoir. 0 Advantageous embodiments of the invention are given in the dependent claims. Advantages of the invention 5 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 0 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 5 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' 5 WO 2013/062417 PCT/N02011/000305 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 5 for determining adjustments to the control of the well. Figure captions Embodiments of the method and device of the invention is illustrated 0 in the attached drawings, wherein 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 5 interval. The downstream piping system and well path to the topside equipment is not illustrated. Nine frames are shown, Fig. 1-1 to 1-9 illustrating the technique. Each frame is a time step and describe how the tracer shots move 0 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. 5 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 0 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. In Fig. 1-3 the well influx has started and each vertical arrow in 5 this example represent a given flow for example 1000 bopd (barrels of oil per day). 6 WO 2013/062417 PCT/N02011/000305 As seen the influx from the zone between tracer C and D is three times higher than the influx between zone A and B. When the tracer slugs start moving with the well fluids as seen in 5 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. The volume and hence time difference between the arrival of slug C 0 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 5 this higher influx, this is also visualized in Figs. 1-6 to 1-9. 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. 0 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 5 measured concentrations of identified tracers. Fig. 4 gives a few rough examples of well fluids wetting tracers generally according to prior art. 0 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 5 granted that the tracers are placed where the influx exactly occurs. 7 WO 2013/062417 PCT/N02011/000305 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 5 than what is illustrated in Fig. 5a and b. 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 0 the fluids with the tracer is eventually flushed out from the isolated zone's completion void. Fig. 6a illustrates one insulated influx zone insulated by a lower (right) and an upper (left) packer defining a zone of influx of 5 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 0 topside. A steady state flow rate is advantageous. 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 5 and flow geometry in the annulus space. 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. 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 5 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 8 WO 2013/062417 PCT/N02011/000305 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 5 lower rate and sustain at a detectable level for longer. 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 o 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. 5 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. O The fluid carries tracer with it at a generally even rate with the production flow. Fig. 8b illustrates the result of a shut-in downstream (topside) in order to build a concentration in the annulus space, called to build 5 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 0 pipe, this is not a problem, but requires a more elaborate well control apparatus. Fig. 8c illustrates that the tracer concentrated fluid (the "shot") is flushed out with resumption of the production by opening the 5 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. 9 WO 2013/062417 PCT/N02011/000305 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 5 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 0 rate, but both may be at a detectable level for very long time. 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 5 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 o 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 5 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 0 typically be used in the context described in Fig. 1 where venting towards the central base pipe is needed. Fig. 11 shows a similar embodiment of the mechanical tracer release sub according to a slightly different embodiment of the invention, 5 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 10 WO 2013/062417 PCT/N02011/000305 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 5 the insulated zone in the annulus void in the completion, and will work along the lines of Fig. 7. Fig. 12 illustrates this mechanical embodiment which releases into the void outside the central production pipe and used in the context 0 shown in Fig. 6 with flush-out from the insulated zone in the annulus void in the completion. 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 5 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 o 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 5 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 0 too late and must be due to a lower influx than presumed. This indicates that the influx model should be adjusted significantly. 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 5 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 11 WO 2013/062417 PCT/N02011/000305 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 5 considered as a candidate for an overhaul. One will now see that the predicted peak arrivals coincide with the actual peaks. As an improvement, further curve analysis could be conducted in order to determine the assumed continuous curve peak arrivals from 0 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 5 The invention is a method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr), 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 o 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 (4m) has a predefined, comparatively short, quickly released dose (V 4 ) (short release time dose) to the fluids 5 in the well. 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 o 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 5 "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. 12 WO 2013/062417 PCT/N02011/000305 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 (tR). The tracer sources according to the invention are arranged to release 5 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 o date and time in order to conduct further measurement series. After the release instant (tR) , samples (c 1 , c 2 , c 3 , ...) of the production flow (F) are consecutively collected at the topside. The sampling may simply be conducted by tapping small amounts of the 5 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 (fi, f 2 , f 3 , f 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 o cumulative productin.) After sampling, the samples (c 1 , c 2 , c 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 5 the identified tracer materials. 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 O in a chemical laboratory in order to provide more precise measurements or for verifying or refining field measurements. Rough calculation Based on the measured concentrations (4c, 41c, 42,, 43c) and their 5 sampling sequence, i.e. sampling times or cumulative production volumes (fl, f 2 , f 3 , f 4 ) and the well geometry, one may calculate the influx volumes (qj) from transient tracer flow models (in a 13 WO 2013/062417 PCT/N02011/000305 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 5 including tie-back pipes, all the way from the influx zones to the topside sampling point. Utilizing calculated influx volumes The calculated influx volumes (qi) are used as parameters for 0 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 5 branches' production pipes into a main well. Refining the calculations 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 0 correspondence in the measured concentration curves and the modeled calculation curves. Decisions based on many parameters The well operator will usually not decide on controlling the well 5 flow only based on the estimates of influx volumes, but use additional relevant parameters such as pressure and fluid composition and other operational parameters. Simultaneous release all or in groups ) 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 (tR) 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 14 WO 2013/062417 PCT/N02011/000305 tracers in subsequent sets of zones with a required sufficient delay until the entire well is covered. Release duration 5 In an advantageous embodiment of the invention, the release dose (Vt) 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 0 chamber, significantly shorter than the characteristic time constant of the delay chamber. Release instant control In an advantageous embodiment of the invention, the given release 5 instant (tR) 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. The given release instant (tR) 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. In an embodiment of the method of the invention the given release instant (tR) may be commanded from the surface. A signal transmitter 15 WO 2013/062417 PCT/N02011/000305 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 5 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. In an advantageous embodiment of the invention, the method is 0 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 5 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. 0 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 5 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. In an embodiment of the invention one may have knowledge of the o 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. 5 In and embodiment of the method of the invention, the sampling is conducted after said predefined release instant (t,), after a time 16 WO 2013/062417 PCT/N02011/000305 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 5 the topside location. 17

Claims (27)

1. A method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations 5 (3) along the well - arranging tracer sources (4) with unique tracer materials (4m) in fluid communication with said influx zones (3), - each said tracer material (4m) having a predefined short duration release dose (Vt 4 ) to the fluids in the well, o - allowing said tracer sources (4) to release said tracer material (4m) to said fluids at a given release instant (tR), - after said release instant (t,), consecutively collecting samples (cl, c 2 , c 3 , ... ) of said production flow (F) at the topside, - analysing said samples (ci, c 2 , c 3 , ... ) for identifying types of 5 tracer material (4m) and concentration of said identified tracer materials (4c), - based on said concentrations (4c, 41c, 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, calculating said influx volumes (q) from transient tracer o flow models - using the calculated influx volumes (qi) as parameters for controlling the production flow or for characterizing the reservoir. 5

2. The method of claim 1, said tracer sources (4) arranged for releasing preferably simultaneously at a given release instant (tR) in time.

3. The method of claim 1 or 2, wherein said release dose (V,,) is 0 released during less than one minute, preferably less than 10 seconds.

4. The method according to any of the preceding claims, wherein said given release instant (tR) being an advance determined instant 5 in time. 18 WO 2013/062417 PCT/N02011/000305

5. The method according to claim 4, said given release instant (tR) being one of a series'of release instants, all predetermined before assembly and installation of the production pipe assembly. 5

6. The method according to any of the preceding claims, said given release instant (tR) being commanded from the surface.

7. The method according to one or more of the preceding claims, said two or more influx locations being separate, influx locations o mutually isolated in the annulus around the production pipe.

8. The method according to one or more of the preceding claims, said tracer sources arranged in fluid communication with said influx zones. 5

9. The method according to one or more of the preceding claims, said influx locations (3) having known positions along the well.

10. The method according to one or more of the preceding claims, o after said release instant (tR), 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 one or more of the preceding claims, 5 collecting said consecutive samples (c 1 , c 2 , c 3 , ... ) of said production flow (F) at the topside at sampling times (t 1 , t 2 , t 3 , . said sampling sequence being sampling times (t 1 , t 2 , t 3 , ...

12. The method according to one or more of the preceding claims, o collecting said consecutive samples (c 1 , c 2 , c 3 , ... ) of said production flow (F) at the topside at consecutive cumulative production volumes (fl, f 2 , f 3 , f 4 ), said sampling sequence being cumulative production volumes (fl, f 2 , f 3 , f 4 ) 5

13. The method according to one or more of the preceding claims, the well geometry comprising the sequence and positions of said separate 19 WO 2013/062417 PCT/N02011/000305 influx zones, and the length and geometry of the production pipe from the influx zones to the topside.

14. The method according to one or more of the preceding claims, 5 said production flow (F) being in a general steady state.

15. The method according to one or more of the preceding claims, said production flow (F) a ramp-up. 0

16. A system for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr) with two or more influx locations (3) along the well, comprising - tracer sources (4) with unique tracer materials (4 m) arranged in fluid communication with said influx zones (3), 5 - each said tracer material (4m) having a predefined short duration release dose (V,,) to the fluids in the well, - said tracer sources (4) provided with a timer to release said tracer material (4m) to said fluids at a given release instant (tR) - a sampling device for consecutively collecting samples (c 1 , c 2 , c 3 , o ...) of said production flow (F) at the topside after said release instant (tR), - an analysing apparatus for said samples (ci, c 2 , c 3 , ... ) for identifying types of tracer material (4m) and concentration of said identified tracer materials (4), 5 - an algorithm for calculating said influx volumes (qj) from transient tracer flow models based on said concentrations (4c, 41c, 42c, 43c) and their sampling sequence and the well geometry, sequence of said separate influx zones, - said calculated influx volumes (qi) for being used as parameters 0 for controlling the production flow or for characterizing the reservoir.

17. The system of claim 16, said tracer sources (4) arranged for releasing preferably simultaneously at a given release instant (tR) 5 in time. 20 WO 2013/062417 PCT/N02011/000305

18. The system of claim 17, wherein said release dose (V 4 ) is arranged for being released during less than one minute, preferably less than 10 seconds. 5

19. The system according to any of the preceding claims 15 - 18, wherein said given release instant (tR) is an advance determined instant in time.

20. The system according to any of the preceding claims 15 - 19, 0 said given release instant (tR) being one of a series of release instants.

21. The system according to any of the preceding claims 15 - 20, said given release instant (tR) arranged for being commanded from the 5 surface.

22. The system according to one or more of the preceding claims 15 21, said two or more influx locations being separate, influx locations mutually isolated in the annulus around the production 0 pipe.

23. The system according to one or more of the preceding claims 15 22, said tracer sources arranged in fluid communication with said influx zones. 5

24. The system according to one or more of the preceding claims 15 23, 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. 0

25. The system according to one or more of the preceding claims 15 24, 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 5 unit arranged in said sub, said sub provided with an electrical battery, each said breakable ampoule provided with a discharge channel to the fluid. 21 WO 2013/062417 PCT/N02011/000305

26. The system according to claim 25, said discharge channel leading to the central production pipe. 5

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. 0 22