The present invention concerns a method and a system for estimating flow rates of fluids from each of separate influx zones in a multilayered reservoir to a production flow in a well in the reservoir.
The method and system may be used for indicating potential crossflow in wells that are draining multilayered reservoirs. The method and system may further be used for estimating influx volumes of fluids from zones in a multilayered reservoir with potential crossflow to a production flow in a well. The fluids may be water, oil, gas.
In multilayered reservoirs the hydrocarbon production flow may be produced from multiple zones having different properties and different backpressures. This results in a situation where the produced hydrocarbons from a zone may flow into the well and out into other zones in the formation,—a phenomenon called crossflow. The effect is mostly experienced when wells are shut in and at low flow rates.
A method for monitoring and characterizing multilayered reservoirs are described in SPE 132596 “Best practices in Testing and Analyzing Multilayer Reservoirs” by Pan et al. and is based on testing and analyzing the pressure transient behavior of the multilayer reservoir in combination with the Selective Inflow Performance (SIP) production logging technique (PLT). In this paper, a production logging tool are measuring the flow profile and well hole pressures in the well during various flow rates. The logging tool is lowered down into the well and dragged up and down in the well providing measurements in the different zones in the well during the procedure. This procedure is very expensive and time consuming and the running of a PLT is not always an option due to poor accessibility. The procedure requires the logging tool inside the well, and thus the use of large equipment for handling the tool; e.g. a drilling vessel. There is also the risk of the logging tool getting stuck in the well with the possible result of completely abandonment of the well.
The present invention provides an optional solution to the problem above without well intervention. The inventive method and system is based on studying tracer flowback behaviour with altering production rates from the well.
The invention provides a method for estimating flow rates of fluids from each of separate influx zones in a multilayered reservoir to a production flow in a well in the reservoir, the well having at least two separate influx zones from the multilayer reservoir of known positions along the well, the well being provided with distinct tracer sources with distinct tracer materials of known positions in each of the at least two separate influx zones. The method comprising providing a global production flow change for the production flow in the well, establishing tracer concentrations in the production flow of the distinct tracer materials as a function of time during the global flow change, and estimating the production rates from each of the separate influx zones in the reservoir. A delay path for a tracer leakout stream flow from each zone in the reservoir may be provided.
In an aspect the invention provides a method for estimating flow rates of fluids from each of separate influx zones in a multilayered reservoir to a production flow in a well in the reservoir, the well having at least two separate influx zones from the multilayer reservoir of known positions along the well, the well being provided with distinct tracer sources with distinct tracer materials of known positions in each of the at least two separate influx zones wherein each influx zone being provided with a delay path for a tracer leakout stream flow from that influx zone, the method comprising:
a) providing a global production flow change for the production flow in the well,
b) establishing tracer concentrations in the production flow of the distinct tracer materials as a function of time, and measuring time delays for tracer concentration changes of the distinct tracer materials from each zone resulting from the global production flow change; and
c) estimating the production rates from each of the separate influx zones in the reservoir.
Each zone may further be provided with a specific entry point for a tracer leakout stream flow from each zone. The tracers may be arranged in the at least two separate influx zones in the multilayer reservoir during completion of the well. The tracers may in an embodiment be arranged in well equipment provided in the well.
In a further embodiment the method may further comprise:
i)—flowing the well at a high production rate,
The method may further comprise repeating the steps i) and ii) for a number of decreasing production rates, monitoring tracer concentration transients in the production flow after each production rate decrease, and estimating the flow contributions from each of the at least two separate influx zones.
Decreasing production rates may comprise gradually decreasing the production flow rate. In an embodiment, the method may comprise establishing the flow rate for which the tracer concentration of at least one of the distinct tracer materials is disappearing from the production flow. In an embodiment the method may comprise gradually decreasing the production flow rate until the at least one distinct tracer material is disappearing from the production flow.
In an embodiment, the method may further comprise gradually decreasing the production flow rate until a tracer concentration of at least one of the specific tracer materials in a sample of the production flow becomes zero.
Decreasing production rates may comprise stepwise decreasing the production flow rate.
The production flow change may comprise stepwise, gradually or continuously decreasing the production flow rate. The production flow change may comprise stepwise, gradually or continuously increasing the production flow rate.
The global production flow change may be provided by a ramp-up.
In an even further embodiment, the method comprising based on said concentrations and their sampling times during gradually decreasing flow rates, establishing the tracer concentration transients after each rate change, and based on the tracer concentration transients after each rate change estimate the flow contributions from each zone, note the rate on which the tracer in a specific zone is disappearing and establishing rate-pressure curves for the different zones in the multilayer reservoir.
The global production flow change may be provided by a flush-out of the tracers. The tracers may be mechanically released from the tracer systems. The fluids may be at least one of water, oil or gas.
In a further aspect the invention provides a system for estimating flow rates of fluids from each of separate influx zones in a multilayered reservoir to a production flow in a well in the reservoir, where the well has at least two separate influx zones from the multilayer reservoir of known positions along the well. The system comprising: distinct tracer sources with distinct tracer materials arranged in known positions in each of the at least two separate influx zones of the well; apparatus for establishing tracer concentrations in the production flow of the distinct tracer materials as a function of time during a global flow change for the production flow in the well; and estimating the production rates from each of the separate influx zones in the reservoir. A delay path is provided for a tracer leakout stream flow from the distinct tracer sources in each influx zone in the reservoir.
The delay path in an influx zone may be provided by a distance between the distinct tracer sources and an entry point for the tracer leakout stream flow into a production baseline of the well.
The tracers may be arranged in the at least two separate influx zones in the multilayer reservoir during completion of the well. The tracers may be arranged in the reservoir formation, in a completion, a casing, a liner, or in equipment provided in the well. The tracers may be mechanically released or released upon interaction with a well fluid.
The method and system above may be used for indicating potential crossflow in wells that are draining multilayered reservoirs. The method and system may also be used for estimating influx volumes of fluids from zones in a multilayered reservoir with potential crossflow to a production flow in a well.
The fluids may be at least one of water, oil or gas.
Example embodiments of the invention will now be described with reference to the followings drawings, where:
a shows an enlarged view of one of the influx zones from
b shows an enlarged view of one of the influx zones from
c illustrates a tracer concentration flow rate (dotted lines C44t C44e) as a function of time in the zone in
d illustrates tracer concentration flow rates (dotted lines C44t C41e C42e C43e) as a function of time from the different zones in the multilayer reservoir illustrated in
a shows rate pressure curves p1, p2, p3 and p4 for a multilayered reservoir with four zones together with indications of the full rate contributions and shutin cross flows for the different zones;
b illustrates creation of rate pressure curves p1, p2, p3 and p4 by step rate changes of the well production rate according to an embodiment of the invention;
The present invention will be described with reference to the drawings. The same reference numerals are used for the same or similar features in all the drawings and throughout the description.
The present invention provides the use of tracers combined with production flow rate changes for the production flow in the production well, and monitoring tracer concentrations. The invention will be explained in detail below.
While the tracer systems are exposed to/wetted by their target fluid (e.g. water or hydrocarbons) there will be a leakage of tracer material from the zones in the reservoir/well. The leak-out rate of tracer material has been tuned to give a detectable signal at the sampling point for a given production rate over the lifetime for the tracer systems. The leakage rate is not dependent on the fluid velocity past the tracer systems, and no such velocity is required for the tracer material to leak into the surrounding fluids as long as the fluids are the target fluids for the given system. For an oil system, oil would be the target fluid and for a water system, water would be the target fluid.
This independence of fluid velocity means that while the well is shut-in and there are no flow past the tracer systems (assuming no cross-flow in the well), a high concentration of tracer material will build up in the vicinity of the tracer systems,—a tracer shot. When the well is opened and the fluids flow towards the surface, the tracer shot will also migrate towards the sampling point of the well. If the tracer concentration in the fluids at the sampling point is measured as a function of time or volume, then the high concentration fluids passing the sampling point will give concentration peaks for each tracer in the well. The tracer concentration peaks and their arrival timing may carry information on zonal contribution.
However, with serious crossflows fluids may never be still and shots may not be able to build. Shutin may also be a scenario that should be avoided from a production angle as explained earlier.
The tracers that may be used in the present invention may be any kind of tracer influenced by the well fluids and for which the concentrations of tracer may be determined.
Non-limiting examples of tracers that may be used in the present invention are described in e.g. WO0181914 and WO2010005319 (both belonging to the applicant of the present invention; Resman A S) which are hereby included by reference in their entirety. Once arranged in the well these tracers may enable monitoring of the well or reservoir for decades.
The tracers used in the present invention may be arranged in the reservoir for the purpose of the invention. Alternatively, tracers already present in the different zones in the reservoir may be used. The tracers may be arranged in the reservoir during completion or in well equipment later installed in the well or reservoir. The tracers may be arranged in the influx zones in the multilayer reservoir during completion of the well. Further, the tracers may be arranged in the reservoir formation, in a completion, a casing, a liner, or in equipment provided in the well.
It may also be envisaged mechanically release of tracers, and establishing tracer transients by using tracer shots.
The multilayered reservoir is in
Tracer sources 41, 42, 43, 44 with distinct tracer materials 41m, 42m, 43m, 44m distinct for each zone are arranged in each influx zone 31, 32, 33, 34. The tracer sources are arranged in known positions in each zone. Each of the distinct tracer materials 41m, 42m, 43m, 44m have known tracer leak-out flux rates ft41, ft42, ft43, ft44 . . . to the surrounding influx fluids in the zone. The tracer leak-out flux rates are independent of fluid flow velocities. Each tracer leakout stream is flushed into the basepipe flow at a velocity proportional to the production rate in the zone and with corresponding flux contributions fcon41, fcon42, fcon43, fcon44.
The tracer leakout streams flow into the basepipe flow at known entry points in each zone together with the production flow from the zone.
A valve 30 is in the embodiment in
The invention will for ease of explanation be further explained in detail below with reference to one of the influx zones in the multilayer reservoir. This is not to be considered limiting for the invention and the principles of the description below holds for all the different influx zones in the multilayer reservoir.
a shows an enlarged view of the influx zone 34 from
In
There is a tracer leak-out flux rate ft44 from the tracers arranged in influx zone 34.
b shows an enlarged view of the influx zone 34 from
The zonal contribution to the production flow Q in the well from the production zone 44 is the flow rate q44 from the formation in this production zone as illustrated in
If the flow rate q44 is changed due to some change in topside or entry point choke setting, this change will immediately impact the tracer concentration C44t (inversely proportional to q44) in the influx (production) zone 34 shown in
If multiple zones are flowed simultaneously in the same well in a multilayered reservoir and during a global choke change, the different tracer concentrations C41e, C42e, C43e, from each zone will all appear at different times and according to the rates in the different zones. This situation is shown in
In an embodiment of the invention, a number of repeating measurements may typically be made. The measurements may be performed for a number of decreasing rates down to zero flow rate Q if possible. The lower flow rate from the present measurement may provide a starting point for the following measurement. The measurements may also be performed for various flow rates serving as starting point for the measurement.
The method of obtaining the rates at varying flow rates as described above may be combined with the principles of Selective Inflow Performance (SIP) method known from Wireline Production Logging, See also SPE 132596 “Best practices in testing and analyzing Multilayer Reservoirs”
The further embodiment of the invention provides choking back the production flow from full rate and monitoring changes in tracer concentration in the fluid flow from each influx zone until the time the concentration of distinct tracer materials from an influx zone (layer 2 in
The production rate contributions from each zone in the reservoir is determined based on the method explained above in relation to
The change in production rate may be accomplished by controlling the valve 30 in the well. The following explanation of the method is for simplicity explained in view of a multilayer reservoir with four zones 44, 43, 42, 41 as illustrated in
a shows the pressures p1, p2, p3, p4 from the different zones in the multilayer reservoir from
a is only for illustration purposes and not limiting for the invention. Other multilayer wells with a multitude of zones may have a different zone for which the tracer concentration is disappearing first. The changes in tracer concentration in the fluid flow may also in this embodiment be monitored online or monitored by taking samples from the fluid flow for later analyses.
The invention may also be performed for increasing pressure changes. The pressure changes may be performed in steps, gradually or continuously. The requirement is a pressure change.
In order to establish the pressure curves p1, p2, p3, p4 from each zone as a function of well production rate a number of repeating measurements (samples) will typically be made. Tracer concentration transients after each rate change are established based on the concentrations and their sampling times during gradually decreasing flow rates, and used in estimating the flow contributions from each zone. The flow rate on which the tracer in a specific zone is disappearing (when the tracer concentration from the zone in a flow becomes zero) is used in establishing the shutin pressure for that zone.
b shows how a measurement during a step rate change creates a point for each zone in the diagram. When a number of points have been established for decreasing step rate changes, the straight lines of the production pressures p1, p2, p3, p4 (rate-pressure curves) from each influx zone are established by drawing up a straight line between the points.
Sampling programs performing the number of repeating measurements are tailormade for each well. Typical sampling programs are as follows:
The down-steps are performed relatively quickly in view of the entire sampling procedure. Typically each down-step is performed in about 15-30 minutes in order to have a controlled and smooth reduction of production flow. The time for each down-step is however tailormade for each well. An (in theory) equal number of samples are taken after each rate step-down. In practice there may be deviations from this, but a small deviation will not have any significance for the functionality. Normally 60-100 samples are taken after each production rate out of which 20-40 samples are analyzed. To establish a base line a more limited number of samples and analyzed samples are normally required. In the example in
The method and system may be used for indicating potential crossflow in wells that are draining multilayered reservoirs. The method and system may further be used for estimating influx volumes of fluids from zones in a multilayered reservoir with potential crossflow to a production flow in a well. The fluids may be at least one of water, oil or gas.
Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.
Number | Date | Country | Kind |
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20120763 | Jul 2012 | NO | national |
Filing Document | Filing Date | Country | Kind |
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PCT/NO2013/050121 | 7/1/2013 | WO | 00 |