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.
The tracer carriers illustrated in
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
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.
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
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.
Problems related to long term release in this context
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
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
Advantageous embodiments of the invention are given in the dependent claims.
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.
Embodiments of the method and device of the invention is illustrated in the attached drawings, wherein
Nine frames are shown,
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
In
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
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
a 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.
b 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
a 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.
b 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.
c 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.
a illustrates a situation similar to what is illustrated in
b 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.
c 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.
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
The invention is a method for estimating influx volumes (qi) of fluids to a production flow (F) in a well (Wr), please see
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.
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 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.
After the release instant (tR), samples (c1, c2, c3, . . . ) 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 (f1, f2, f3, f4), 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.)
After sampling, the samples (c1, c2, c3, . . . ) 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.
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.
Rough Calculation
Based on the measured concentrations (4c, 41c, 42c, 43c) and their sampling sequence, i.e. sampling times or cumulative production volumes (f1, f2, f3, f4) and the well geometry, one may calculate the influx volumes (qi) 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.
Utilizing Calculated Influx Volumes
The calculated influx volumes (qi) 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.
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 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 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 tracers in subsequent sets of zones with a required sufficient delay until the entire well is covered.
Release Duration
In an advantageous embodiment of the invention, the release dose (Vt4) 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.
Release Instant Control
In an advantageous embodiment of the invention, the given release 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 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.
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.
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
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.
In and embodiment of the method of the invention, the sampling is conducted after said predefined release instant (tR), 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.
To be filed as a PCT patent application on Oct. 28, 2011 without any preceding application
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NO2011/000305 | 10/28/2011 | WO | 00 | 5/6/2014 |