Method and system for monitoring oil production well

Abstract

The invention provides a method of estimating an oil flow characteristic from a hydrocarbon reservoir to a production well with two or more influx zones or influx locations to a production flow. The well comprises at least one tracer source with distinct tracer in known levels of the production well. The method comprising producing fluid in the well from the reservoir and collecting at least one gas phase sample from the produced fluid. The method comprising analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer and based on the presence and / or concentration of the at least one tracer in the at least one sample estimating an oil flow characteristic.

Description

[0001] Method and System for Monitoring Oil Production Well

[0002] The present invention relates to monitoring flow from a reservoir to a production well. In particular the present invention relates to a method of monitoring flow from the reservoir using tracer material. Aspects of the invention relate to a system and method of determining oil flow characteristics from a reservoir.

[0003] Background to the invention

[0004] Optimal oil and gas production from a hydrocarbon reservoir reguires reliable knowledge of the characteristics of the reservoir and production well. It is known to use tracers as a monitoring technigue to measure the migration of fluid flow in hydrocarbon wells for a number of applications including verifying a clean-up process during the completion of a well, determine flow paths between different reservoir units and detect water breakthrough. Tracers are released into a flow at an upstream and detected at a downstream location. Detecting tracer concentration downstream may infer information about flow paths and flows rates in the well.

[0005] Generally, two types of tracers are used in the oil and gas industry to monitor flow namely radioactive tracers and chemical (non-radioactive) tracers. Chemical tracers include water tracers, oil tracers and gas tracers. Oil tracers are designed to release when in contact with oil and are used to trace the flow of oil. Waters tracers designed to release when in contact with water and are used to trace the flow of water. Sampling of produced liguids and detecting the presence of tracer may infer information on water and / or oil in the reservoir and well. Gas tracers are used to trace the flow of production gas.

[0006] Produced liguids comprise a mixture of solid and liguid contaminates including oil field chemicals, anionic and cationic salts, acids, sands, silts, clays, bacteria and well treatment chemicals which can interfere with sample processing and affect the detection limits of tracers. The collection, storage and processing of a large number produced liguid samples is complex and can be expensive. Furthermore some countries have restrictions in place on the processing and shipping of oil samples containing oil tracers. Summary of the invention

[0007] There is generally a need for a method and system for monitoring a reservoir which addresses one or more of the problems identified above.

[0008] It is amongst the aims and objects of the invention to provide system and method for determining oil flow characteristics from a hydrocarbon reservoir based on collected gas phase samples.

[0009] It is an object of the present invention to provide a method of estimating an oil influx profile to a producing hydrocarbon well with two or more influx zones based on tracer data in collected gas samples.

[0010] It is another object of the present invention to provide a tracer capable of associating with oil in a liquid phase at a known level of a production well and associating with a gas phase downhole before it reaches a sampling location.

[0011] It is a further object of an aspect of the invention to provide a method for monitoring the production from different zones / sections along a well bore in a reservoir using one or more tracers capable of associating with oil at the different zones / sections in a liquid phase and associating with the gas phase at a detection point.

[0012] Further aims and objects of the invention will become apparent from reading the following description.

[0013] According to a first aspect of the invention, there is provided a method for estimating an oil flow characteristic from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow; providing at least one tracer source with distinct tracer in at least one known level of a production well; producing fluid in the well from the reservoir, collecting at least one gas phase sample from the produced fluid; analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the at least one gas phase sample estimating an oil flow characteristic. The at least one tracer source may be configured to release distinct tracer material into one or more fluid phases. The at least one tracer source may be configured to release distinct tracer material into one or more fluid phases miscible but distinguishable from oil.

[0014] The at least one gas sample may be a non-oleic sample. The method may comprise collecting at least one non-oleic phase sample from the produced fluid. The method may comprise analysing the at least one non-oleic phase sample for the presence and / or concentration of the at least one tracer. The method may comprise estimating an oil flow characteristic based on the presence and / or concentration of the at least one tracer in the at least one non-oleic sample. The method may comprise preserving and / or transporting non-oleic phase samples. The method may comprise preserving and / or transporting non-oleic phase samples for later analysis.

[0015] The method may comprise calculating, determining and / or monitoring an oil flow characteristic from a hydrocarbon reservoir to a production well with two or more influx zones or influx locations to a production flow.

[0016] The oil flow characteristic may comprise one or more influx rates of fluids from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the at least one influx zone. The oil flow characteristic may comprise the influx rate of fluids from the at least one influx zone. The oil flow characteristic may comprise the influx rate of oil from the at least one influx zone. The oil flow characteristic may comprise an influx profile for the at least one influx zone. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from the at least one influx zone. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0017] The production well may have two or more influx zones or influx locations to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The oil flow characteristic may comprise one or more influx rates of fluids from the two or more influx zones. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0018] The method may comprise arranging, installing, integrating and / or positioning tracer sources with distinct tracers in known levels of the well. The method may comprise arranging, installing and / or positioning at least one of the tracer sources at, upstream and / or downstream of at least one influx zone. The method may comprise arranging, installing and / or positioning at least one of the tracer sources exposed to well fluids in at least one of said influx zones. The method may comprise arranging, installing and / or positioning at least one of the tracer sources exposed to oil fluid in at least one of said influx zones. The method may comprise arranging, installing and / or positioning a different and / or distinct tracer source at each influx zone.

[0019] The at least one tracer may be a two phase associating tracer. The at least one tracer may be configured to associate with a first phase under a first condition and / or first location. The at least one tracer may be configured to associate with a second phase under a second condition and / or second location.

[0020] The at least one tracer may be configured to release from a tracer source into liquid oil phase. The at least one tracer may be released from the tracer source with an even release rate. The at least one tracer may be released from the tracer source into liquid oil phase with an even release rate. The at least one tracer may be designed to release from the tracer source when in contact with liquid oil phase. The at least one tracer may be configured to associate with oil in a liquid phase at the known level of a production well. The method may comprise releasing the tracer from a tracer material into the oil liquid phase at the point of contact with the oil at the known level of a production well. The at least one tracer may be configured to associate with oil in a liquid phase at the influx zone of a production well. The at least one tracer may be configured to be present in a liquid phase at a release location.

[0021] The at least one tracer may be configured to associate with a gas phase downhole before it reaches a sampling location. The at least one released tracer may be configured to associate with a gas phase. The at least one tracer may be configured or selected to associate with a gas phase downhole before it the surface. The at least one tracer may be configured to associate with a gas phase in the upper completion of the well. The at least one tracer may be configured to be present in a gas phase at a detection location. The method may comprise sampling the gas phase for the presence or absence of the at least one tracer.

[0022] The at least one tracer may be a hydrocarbon tracer. The at least one tracer may be an oil tracer. The at least one tracer may be a fluid specific tracer. The at least one tracer may be a liquid specific tracer. The at least one tracer may be an oil tracer capable of being released from a tracer source when in contact with oil. The tracer may be an oil tracer capable of being detectable in the gas phase. The tracer may be an oil tracer capable of being carried by oil flow.

[0023] The at least one tracer may comprise chemical and physical properties to associate predominantly in the liquid phase at high pressure and / or temperature conditions such as those at downhole tracer release location conditions. The at least one tracer may comprise a volatile nature capable of associating predominantly in the liquid phase at high pressure and / or temperature conditions such as those at downhole tracer release location conditions. The at least one tracer comprises chemical and physical properties to associate predominantly in the gas phase at lower pressure and temperature conditions such as those at sampling location conditions. The at least one tracer may comprise a volatile nature capable of associating predominantly in the gas phase at lower pressure and temperature conditions such as those at sampling location conditions.

[0024] The at least one tracer may comprise at least one stable organic compound. The at least one tracer may comprise a stable organic compound not naturally present in the hydrocarbon well. The at least one tracer may comprise chemical tracers selected from the group comprising perfluorinated hydrocarbons or perfluoroethers. The at least one tracer may comprise a partly fluorinated compound. The perfluorinated hydrocarbons may be selected from the group of perfluoro buthane (PB), perfluoro methyl cyclopentane (PMCP), perfluoro methyl cyclohexane (PMCH).

[0025] The at least one tracer may have a low detection limit. The method may comprise detecting the at least one tracer in amounts less than 100 part per million volume per volume. The method may comprise detecting the at least one tracer in amounts less than 1 part per billion volume per volume. The method may comprise detecting the at least one tracer in amounts less than 100 parts per trillion volume per volume. The method may comprise detecting the at least one tracer in amounts less than 10 parts per trillion volume per volume. The method may comprise detecting the at least one tracers in amounts as low as 1 part per trillion (1012) volume per volume. The method may comprise detecting the at least one tracer in amounts less than 1 part per trillion volume per volume.

[0026] The method may comprise separating the produced gas phase hydrocarbons from liquid phase hydrocarbons. The method may comprise separating the produced gas phase hydrocarbons from liquid phase hydrocarbons before sampling.

[0027] The method may comprise collecting the at least one sample at one or more sampling times. The method may comprise collecting the at least one sample downhole downstream of the tracer release location or at surface. The at least one sample may be collected for later analysis onsite or offsite. The sample of produced gas phase may be measured in real time. The collected at least one sample may be preserved for future testing. The at least one sample may be collected in at least one collection device. The at least one collection device may be configured to preserve the sample for future testing The at least one collecting device may be configured to preserve the at least one sample for later analysis. The at least one collecting device may be configured to preserve the at least one gas phase sample for later analysis. The at least one collection device may be a storage device.

[0028] The method may comprise storing collected samples in a storage device. The method may comprise storing collected samples in a storage device for export to a laboratory and / or later analysis. The gas samples may be stored by adsorbing them to a chemical adsorption tube (CAT).

[0029] The method may comprise collecting the at least one sample of a predefined volume of gas either pressurized or at ambient pressure. The method may comprise collecting the at least one gas sample under pressure or at ambient pressure. The method may comprise collecting the at least one sample in at least one gas sample container or sampling tube. The method may comprise collecting the at least one sample in a gas sample container such as PVT sample canisters or isotubes. The method may comprise collecting the at least one sample in a deformable container, a bag and / or a balloon. The method may comprise collecting the at least one sample in at least one sampling tube comprising a sorbent material. The sorbent material may be configured to adsorb the at least one tracer. The method may comprise extracting the at least one tracer from the gas sample to the sorbent material. The method may comprise storing and / or transporting the sorbent material. The method may comprise storing and / or transporting the sorbent material for later analysis. The method may comprise designing or selecting the sorbent material having suitability affinity for at least one tracer to capture the at least one tracer present in the gas sample. The method may comprise designing or selecting the sorbent material having suitability affinity for at least one tracer to desorb the at least one tracer from the sorbent material during an analysis technique. Samples may be collected and / or measured downstream at known sampling times. The method may comprise collecting at least one sample at a pre-determined time sequence or predetermined profile. The method may comprise adjusting the sample volume and / or sampling time. The sampling sequence, duration and / or frequency may be modified during the sampling operation.

[0030] The method may comprise analysing the at least one sample to measure the presence and / or concentration of the at least one tracer in the gas sample. The method may comprise analysing the gas samples for type and / or concentration of the at least one tracer as a function of sampling time. The method may comprise analysing the sorbent material to determine tracer data. The method may comprise analysing the sorbent material for the presence and / or concentration of the at least one tracer.

[0031] The method may comprise releasing or extracting the at least one tracer from the sorbent material. The method may comprise analysing the sorbent material to detect the presence and / or concentration of the at least one tracer.

[0032] The method may comprise detecting and / or measuring the concentration of the at least one tracer in at least one gas sample. The method may comprise detecting and / or measuring the concentration of the at least one tracer in the produced gas phase. The method may comprise detecting and / or measuring the concentration of the at least one tracer in the produced gas phase in real time. The method may comprise detecting and / or measuring the concentration of the at least one tracer in the sorbent material. The method may comprise detecting and / or measuring the concentration of the at least one tracer in the produced gas phase using an online analyser. The method may comprise analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer onsite and / or in real time.

[0033] The at least one tracer may be detected and its concentration measured by sampling gas from the production well. The sampling may be achieved by a sampling probe or device arranged in the flow of produced gas. The sampling probe or device may be located downhole or at surface. The sampling may be conducted at the one or more of said sampling times. The at least one tracer may be detected by a detection device such a sensor. The detection device may facilitate real time monitoring and / or analysis of the tracer in the flow of produced gas phase. The real time monitoring and / or analysis may be achieved by a detector probe. The detector probe may be arranged in the flow of produced gas phase. The detector probe may be located downhole or at surface.

[0034] The method may comprise conducting optical monitoring for the detection and / or concentration of the at least one tracer in the produced gas phase. The method may comprise determining the type of tracer. The method may comprise the measuring and / or monitoring the concentration of tracer. The method may comprise the measuring and / or monitoring the transport time of the at least one tracer. The method may comprise detecting and / or measuring the at least one tracer in the gas sample using optical detection, optical fibers, spectrophotometric methods, spectrometric methods and / or chromatographic methods, e.g. Gas Chromatography, Gas Chromatography Tandem Mass Spectrometry (GC-MSMS) or Gas Chromatography-Electron Capture Detector (GC -ECD), MS (mass spectrometry) and / or radioactivity analysis. The invention is not restricted to the above-mentioned techniques.

[0035] The method may comprise estimating an oil influx profile to the producing well with two or more influx zones. The method may comprise estimating an oil influx profile to the producing well with two or more influx zones based on the concentration of the at least one tracer as a function of sampling time. The method may comprise estimating or calculating an oil influx profile to a producing well with at least one influx zone based on a measured tracer response. The method may comprise estimating or calculating an oil influx profile to a producing well with at least one influx zone based on characteristics of the tracer response. Based on the measured concentrations and their sampling sequence and / or the well geometry the influx volumes may be calculated. The sampling sequence, duration and / or frequency may be modified based on measured tracer data. The sampling sequence, duration and / or frequency may be modified based on a model. The influx volumes may be calculated from transient flow models. The influx volumes may be used to estimate the influx profile of the well. The method may comprise using the calculated influx profile as parameters for controlling the production flow or for characterizing the reservoir.

[0036] The method may comprise modelling and / or interpreting the influx rates in a model well. The modelled influx profile and / or rates may be adjusted until the calculated concentrations of model tracers compare with the measured concentrations of identified tracers to estimate an influx profile.

[0037] The method may be a computer-implemented method. The method may be a computer- implemented history matching method. The method may comprise storing the measurement data to a database. The method may comprise storing the model data to a database.

[0038] The method may comprise separating gas from produced liquid. The method may comprise separating at least one gas sample from the produced fluid. The method may comprise inferring information on produced oil from the tracer data in the at least one gas sample.

[0039] The tracer source may comprise a tracer and a carrier. The carrier may be a matrix material. The matrix material may be a polymeric material. The tracer may be chemically immobilized within and / or to the carrier. The tracer source may be chemically immobilized by a chemical interaction between the tracer and the carrier. The tracer source may be chemically immobilized in a way that it releases tracer molecules or particles in the presence of a chemical trigger. By varying the chemical interaction between the tracer and the polymer the release mechanism and the rate of release of tracer molecules from the tracer source may be controlled. Preferably the tracer is released from the tracer carrier with an even release rate. The carrier may be a selected from poly methyl methacrylates (PM MA), poly methylcrylates, poly ethylenglycols (PEG), poly lactic acid (PLA) or poly glycolic acid (PGA) commercially available polymers or copolymers thereof. The carrier may be selected from polymers with higher rates of tracer molecules release such as polyethylene and polypropylene. The tracer may be physically dispersed and / or physically encapsulated in the carrier. The tracer source may release tracer molecules into fluid by dissolution or degradation of the carrier and / or the tracer into the fluid. The carrier may be selected to controllable degrade on contact with a fluid. The carrier may be selected to degrade by hydrolysis of the carrier. The tracer and / or the carrier may be fluid specific such that the tracer molecules will be released from the tracer material as a response to a contact with a target liquid. The tracer and / or the carrier may be fluid specific such that the tracer molecules will be released from the tracer material as a response to a contact with liquid oil phase.

[0040] The tracers and / or the carrier may be chemically intelligent such that tracer molecules will be released from the tracer material as a response of specific events, e.g. they respond to an oil flow (oil-active) but show no response to a water flow (water-resistant). Another group of chemical compounds can be placed in the same region, which release tracers in water flow (water-active) but show no response to an oil flow (oil-resistant). The tracers and / or the carrier may be chemically intelligent such that tracer molecules will be released from the tracer material as a response the exposure of the tracer source to oil in the liquid phase. The released tracer may be configured to associate with gas phase.

[0041] The method may comprise inducing a tracer transient in the flow. The method may comprise inducing a transient in the flow rate. The method may comprise inducing a transient in the flow rate to create a tracer transient. The method may comprise releasing a build-up of tracer in a pulse or short duration to create a tracer transient. The transients may be induced by shutting-in the well or otherwise changes in the flow. Inducing a transient may create a build-up tracer concentration in the locality of the tracer source. On production the built up tracer concentration may propagate to the surface as a high concentration tracer clouds, slugs or shots. The tracer transients are driven by the velocity field in the well. The topside arrivals of the onset of the different tracers, or the full transient of the different tracers, can be used to estimate the downhole velocity field. From the velocity field the inflow profile may be calculated.

[0042] The concentration of tracers at surface as a function of time may be related to the influx into the well, by the velocity field. The tracer concentrations may be governed by the velocity field. The velocity field may be influenced by the well geometry and transport path of the fluid flow.

[0043] A model may be used based on the well geometry of the production well that assumes a specific scenario of inflow distribution, simulates the arrival time of the tracer peaks, and compares the simulated results to the actual peak arrivals. After several iterations, the model may converge on a solution that provides an inflow distribution that best fits the actual data. The model may include a model transport path corresponding to the actual well's transport path downstream of the influx zones. The model may comprise an influx model corresponding to the real influx locations, a tracer system model and having even model leak or release rate corresponding to the real tracer sources and a model well transport path corresponding to the actual production well. The model may comprise parameters selected from the group comprising well geometry, rock mechanics, temperature, pressure, density, viscosity; reservoir permeability, reservoir heterogeneities, solubility, fluid chemistry, phase information, porosity, fluid saturation, flow rate, tracer type, physical behaviour of the tracer, tracer concentration, tracer release rate, migration path of tracer(s), chemical behaviour of hydrocarbon fluids.

[0044] The method may comprise updating the model based upon measured and / or calculated data. The method may comprise history matching. The method may comprise comparing historical parameter measurements to calculated data. The method may comprise adjusting one or more parameter measurements of the model until a reasonable match is achieved between the measured and calculated data. The model may simulate characteristics of the reservoir. The model may simulate characteristics of the flow from the reservoir to the well. The method may comprise comparing modelled tracer gas phase sample data to measured tracer gas phase sample data.

[0045] The tracer concentration may be calculated as a function of time. The measured tracer concentrations may be compared with modelled tracer concentrations to derive information about downhole inflow profiles. Model concentrations for each tracer material may be calculated in a modelled downstream well flow transport path as a function of time under a modelled transient occurring in the model.

[0046] By sampling and analysing gas phase samples from the well rather than liquid samples, the presence of liquid or solid contaminants is mitigated which may improve the sample processing. The detection limit of the tracer in the gas phase may be improved when compared to liquid phase sampling and analysis.

[0047] The installation of tracer source, collection of gas samples, detection, analysis and / or interpretation of tracer data in produced gas phase may be considered as separate methods from one another and performed at different times or jurisdictions. The detection, analysis and / or interpretation of tracer in produced gas phase may be separate methods to release of tracer from the tracer sources and / or the collection of samples. Samples may be collected and the tracer detected, analysed and / or interpreted at a time or jurisdiction which is separate and distinct from the location of well and therefore the collection of the samples.

[0048] According to a second aspect of the invention, there is provided a method for estimating an oil flow characteristics from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source with distinct tracer in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting gas phase samples from the produced fluid; analysing the gas phase samples for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the samples estimating an oil flow characteristic.

[0049] The method may comprise arranging, installing, integrating and / or positioning the tracer sources in known levels of the well.

[0050] The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones. Embodiments of the second aspect of the invention may include one or more features of the first aspect of the invention or its embodiments, or vice versa.

[0051] According to a third aspect of the invention, there is provided a method of estimating an oil influx profile to a producing hydrocarbon well with at least one influx zone or influx location to a production flow; the method comprising: providing at least one tracer source with distinct tracer in at least one known level of a production well; producing fluid in the well from the reservoir, collecting gas phase samples from the produced fluid; analysing the gas phase samples for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the samples estimating an oil influx profile.

[0052] The at least one tracer source may be installed, positioned, placed or integrated in known levels of the production well.

[0053] The method may comprise estimating or calculating an oil influx profile to a producing well with at least one influx zone based on the concentration of the at least one tracer as a function of sampling time.

[0054] The method may comprise estimating or calculating an oil influx profile to a producing well with at least one influx zone based on a measured tracer response. The method may comprise estimating or calculating an oil influx profile to a producing well with at least one influx zone based on characteristics of the tracer response.

[0055] The well may comprise two or more influx zone or influx location to a production flow.

[0056] The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0057] The method may comprise inducing a transient in the flow rate to create a tracer transient. The method may comprise creating a model to simulate characteristics of the flow from the reservoir to the well and comparing modelled tracer gas phase sample data to measured tracer gas phase sample data.

[0058] Embodiments of the third aspect of the invention may include one or more features of the first or second aspects of the invention or their embodiments, or vice versa.

[0059] According to a fourth aspect of the invention, there is provided a method of estimating an oil influx profile to a producing hydrocarbon well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source with distinct tracer in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting gas phase samples from the produced fluid; analysing the gas phase samples for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the samples estimating an influx profile.

[0060] The at least one tracer source may be installed, positioned, placed or integrated in known levels of the production well. The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0061] Embodiments of the fourth aspect of the invention may include one or more features of any of the first to third aspects of the invention or their embodiments, or vice versa.

[0062] According to a fifth aspect of the invention, there is provided a method of collecting samples for analysis in estimating oil flow characteristic and / or estimating an oil influx profile from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting at least one gas phase sample from the produced fluid.

[0063] The method comprising collecting the at least one gas phase sample from the produced fluid in a collection device configured to preserve the at least one sample for later analysis.

[0064] The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0065] Embodiments of the fifth aspect of the invention may include one or more features of any of the first to fourth aspects of the invention or their embodiments, or vice versa.

[0066] According to a sixth aspect of the invention, there is provided a method for estimating an oil flow characteristic from a hydrocarbon reservoir to a production well with at least one influx zones or influx locations to a production flow; wherein the well comprises at least one tracer source in at least one known level of the production well, the method comprising: analysing gas samples for the presence and / or concentration of the at least one tracer as a function of sampling time, the samples previously collected from the production flow at a location downstream of the tracer sources after producing fluid from the production well; based on the presence and / or concentration of the at least one tracer in the samples estimating an oil flow characteristic.

[0067] The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0068] Embodiments of the sixth aspect of the invention may include one or more features of any of the first to fifth aspects of the invention or their embodiments, or vice versa.

[0069] According to a seventh aspect of the invention, there is provided a method of estimating an oil influx profile to a producing hydrocarbon well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source with distinct tracer in at least one known level of the production well, the method comprising: analysing gas samples for the presence and / or concentration of the at least one tracer as a function of sampling time, the samples previously collected from the production flow at a location downstream of the tracer sources after producing fluid from the production well; based on the presence and / or concentration of the at least one tracer in the samples estimating an influx profile.

[0070] The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones.

[0071] Embodiments of the seventh aspect of the invention may include one or more features of any of the first to sixth aspects of the invention or their embodiments, or vice versa. According to an eighth aspect of the invention, there is provided a system for estimating oil flow characteristics from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow, the system comprising: at least one tracer source with distinct tracer configured to be installed in at least one known level of the well; at least one collection device configured to collect at least one gas sample of well fluid downstream of at least one or more influx zones.

[0072] The system may comprise a tracer analyser for analysing presence, type and / or concentration of the at least one tracer.

[0073] The system may comprise a processor. The processor may be configured to determine an oil flow characteristics from a hydrocarbon reservoir to a production well based on the presence and / or concentration of the at least one tracer in the samples as a function of time.

[0074] There may be two or more influx zone or influx location to a production flow. Tracer sources with distinct tracer may be provided in known levels of a production well. Tracer sources with distinct tracer may be provided in two or more known levels of a production well. The system may be configured to estimate or calculate an oil flow characteristic of the two or more influx zones.

[0075] Embodiments of the eighth aspect of the invention may include one or more features of any of the first to seventh aspects of the invention or their embodiments, or vice versa.

[0076] According to a ninth aspect of the invention, there is provided a system for estimating an oil influx profile fluid to a producing hydrocarbon well with at least one influx zone or influx location to a production flow, the system comprising: at least one tracer source with distinct tracer material configured to be installed in at least one known level of the well; at least one collection device configured to collect at least one gas sample of well fluid downstream of at least one influx zone.

[0077] There may be two or more influx zone or influx location to a production flow. The system may be configured to estimate or calculate an oil flow characteristic of the two or more influx zones.

[0078] The system may comprise a tracer analyser for analysing presence, type and / or concentration of the at least one tracer. The system may comprise a processor. The processor may be configured to estimate an oil influx profile. The processor may be configured to estimate an oil influx profile based on the presence and / or concentration of the at least one tracer in the samples as a function of time.

[0079] The at least one collection device may be configured to collect at least one gas sample of well fluid downstream of the two or more influx zones.

[0080] The collection device may be selected from the group comprising sampling tube, chemical adsorption tube, isotube, PVT sample canister, bag and / or a balloon.

[0081] The at least one tracer may be selected from the group comprising stable organic compounds, perfluorinated hydrocarbons, perfluoroethers, partly fluorinated compounds, perfluoro buthane (PB), perfluoro methyl cyclopentane (PMCP) and / or perfluoro methyl cyclohexane (PMCH).

[0082] Embodiments of the ninth aspect of the invention may include one or more features of any of the first to eighth aspects of the invention or their embodiments, or vice versa.

[0083] According to a tenth aspect of the invention, there is provided a method for monitoring oil production from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source with distinct tracer in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting gas phase samples from the produced fluid; analysing the gas phase samples for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the samples monitoring oil production from the at least one influx zone.

[0084] The well may comprise two or more influx zone or influx location to a production flow. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well. The method may comprise estimating or calculating an oil flow characteristic of the at least one influx zone. The method may comprise estimating or calculating an oil flow characteristic of the two or more influx zones. The oil flow characteristic may comprise one or more influx rates and / or volumes from the at least one influx zone. The oil flow characteristic may comprise one or more influx volumes from the two or more influx zones. The oil flow characteristic may comprise the influx rate of fluids from each of the two or more influx zones. The oil flow characteristic may comprise the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise an influx profile for the two or more influx zones. The method may comprise estimating, calculation and / or monitoring the influx rate of oil from each of the two or more influx zones. The oil flow characteristic may comprise influx rate from one or more zones. The oil flow characteristic may comprise influx volume from one or more zones. Based on the presence and / or concentration of the at least one tracer in the samples monitoring oil production from each of the two or more influx zones.

[0085] Embodiments of the tenth aspect of the invention may include one or more features of any of the first to ninth aspects of the invention or their embodiments, or vice versa.

[0086] According to an eleventh aspect of the invention, there is provided a method for estimating an oil flow characteristic from a hydrocarbon reservoir to a production well at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source releasing distinct tracer material into one or more fluid phases miscible but distinguishable from oil in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting at least one non-oleic phase sample from the produced fluid; analysing the at least one non-oleic phase sample for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the at least one non-oleic sample estimating an oil flow characteristic. The method may comprise providing tracer sources with distinct tracer in known levels of a production well. The method may comprise providing tracer sources with distinct tracer in two or more known levels of a production well.

[0087] Embodiments of the eleventh aspect of the invention may include one or more features of any of the first to tenth aspects of the invention or their embodiments, or vice versa.

[0088] Brief description of the drawings

[0089] There will now be described, by way of example only, various embodiments of the invention with reference to the drawings, of which:

[0090] Figure 1 is a simplified sectional diagram through a production well with four influx zones and a tracer source installed at each zone in accordance with an aspect of the invention.

[0091] Detailed description of preferred embodiments

[0092] Figure 1 is a simplified section through a production well 10. A central production tubing 12 is arranged in the well surrounded by annulus 11. Influx volumes of fluids enter the well from a reservoir into the central production tubing 12 via separate influx locations.

[0093] Tracer sources 16 are installed in or on the production tubing and are arranged near each influx location.

[0094] In this example, there are four influx locations 14a, 14b, 14c and 14d and four tracer sources 16a, 16b, 16c and 16d each tracer source has a distinct tracer material for each influx location. However, it will be appreciated that there may be a different number of influx zones and / or tracer sources than illustrated in Figure 1 , for example there may be at least one influx zone.

[0095] In this example the tracer sources are rods of polymeric matrix containing chemical tracers. The chemical tracers and polymer matrix are stable and inert in a wide range of well conditions. It will be appreciated that additionally or alternatively the tracers may be installed or positioned at known levels of the well using tracer release apparatus such as integrating tracer release apparatus as part of the well completion either by integrating into hardware in the well, or adding hardware with the tracer systems integrated into. The tracers are designed to release from the tracer source when in contact with oil and the released tracers have sufficient volatile nature to associate predominantly into the gas phase at lower pressure and temperature conditions such as the conditions at the upper completion location and / or sampling location. In this example the tracers comprise stable organic compounds that are not naturally present in the hydrocarbon well. The stable organic compounds have low detection limits.

[0096] The tracer sources 16a, 16b, 16c, 16d are designed to release tracer when contacted with liquid oil phase. The released tracer is carried with the production flow to the surface. During transport of well fluid to surface the wellbore conditions change reducing temperature and / or pressure and gas evolves from the well fluid. The released tracer is configured to partition to the gaseous phase and associate with the gas phase.

[0097] Sampling and / or analysis of the gas phase at surface provides information on which tracers are present in the gas samples and / or their concentration. This provides information on which influx location in contact with oil and / or are producing oil. It may also provide information on rates of influx. In this example samples of the gas phase are taken at surface. The sampling comprises collecting a predefined volume of gas either pressurized or at ambient pressure. The gas sample is collected in a gas sample container such as PVT sample canisters or isotubes. The gas sample is then analysed to measure the presence and concentration of tracer in the gas sample.

[0098] Alternatively sampling may comprise collecting a predefined volume of gas at ambient pressure. The gas sample is collected in sampling tubes or bag comprising a sorbent material. The sorbent material adsorbs tracers in the gas sample. The tracer is extracted from the gas sample to the sorbent material. The sorbent material may be stored and / or transported to an offsite laboratory for later analysis. The sorbent material may then be analysed to release the tracer, measure the presence and / or concentration of tracers. The affinity of the sorbent material to the tracer is designed or selected so that it sufficiently captures any tracers in the gas sample and also allows desorption of the tracer from the sorbent material during sample analysis techniques.

[0099] In another additional or alternative sampling method a predefined volume of gas at ambient pressure may be collected in a sampling bag or balloon. The sampling bag or balloon may be stored and / or transported to an offsite laboratory for later analysis. A known volume of gas may be extracted from the sampling bag or balloon for analysis. This may be done by transferring the sample directly to piece of equipment to perform tracer analysis such as a GC-MSMS I GC-ECD. Alternatively a known volume of the sample from the sampling bag or balloon may first be transferred to a container containing sorbent material such as a chemical adsorption tube where the sorbent material absorbs the tracer from the gas sample. The sorbent material may later be tested for the presence and / or concentration of tracer.

[0100] In this example the collected samples are analysed in a laboratory offsite. The collected and stored gaseous samples are transported and handled in a sustainable and safe manner. However, it will be appreciated that alternatively or additionally other sampling techniques may be used that allow analysis onsite or in real time. Sampling may include sampling probes or apparatus in the gas phase flow to perform real time sampling and tracer measurements.

[0101] The samples were analysed by GC-MSMS. It will be appreciated that alternatively or additionally other sampling analysis techniques may be used such as optical detection, gas chromatography, GC-ECD, mass spectroscopy, PCR techniques combined with sequential analysis, radioactivity analysis or other separation and detection methods.

[0102] The samples are taken at known sampling times and / or at sufficient frequency depending on purpose of the tracer analysis. Sampling frequency can range from a sample taken every minute to 1 sample per year. The gas phase typically travels faster than oil phase through the upper part of the completion as gas evolves from oil. The oil tracer concentrations in the gas phase arrives earlier than for liquid phase oil so a rapid sampling techniques is used in this example to capture the gas phase tracer data. Typically in rapid sampling techniques samples are taken every 5 minutes. For longer term continuous sampling one sample may be collected each day, week or month.

[0103] The collected gas phase samples may be analysed to identify the type of tracer. The collected gas phase samples may be analysed to measure the concentration of tracer.

[0104] The tracer data may be analysed to provide information about the oil influx profile of the well. Tracer concentration signals of tracer from the various influx zones may be compared and evaluated to derive information about the zonal oil productivity.

[0105] In the example shown in Figure 1, the production is restarted after a shut-in. In any zones where oil is present, the liquid oil phase contacts the installed tracer source in the particular zone and releases tracer. The released tracer is carried to the surface with the production flow. Gas samples of the produced fluids are taken at surface regular sampling times (every 5 minutes). The samples are collected in collection tubes at ambient temperatures. The samples are transported to a laboratory and the samples are analysed for tracer type and tracer concentration recorded at each sampling time.

[0106] In this example the tracer data showed tracers from tracer sources 16a, 16b and 16c were detected in the gas samples. None of the samples comprised tracer 16d indicating the oil is not present at influx location 14d.

[0107] The tracer concentrations of tracers 16a, 16b and 16c in the gas samples were further analysed as a function of time. During shut in the tracer 16a, 16b and 16c were in contact with liquid oil phase and released to the oil at an even rate with time. During shut tracers 16a, 16b and 16c released a high concentration of tracer in the form of a “tracer cloud” localised at the influx zone and tracer source. By analysing the time each of the tracers arrive in the gas samples and / or their concentration over time may provide information on how the release tracer clouds are transported to surface.

[0108] During the production in well, the time to travel to surface from each influx zone is not the same, because the well geometry and distance from the influx locations to the surface are not the same for each influx locations and because the fluid velocity vary as the fluid moves from the influx locations along the well bore to the surface.

[0109] The tracer data collected from the gas samples at the detection point may be analysed to identify the arrival of the concentration peaks of each tracer to determine the inflow distribution which occurs between tracer locations. The volume between the arrival of each tracer peak may be proportional to the inflow that occurs upstream of each tracer. During production, the released tracers from distinctive tracer sources 14a, 14b, 14c at each respective influx zone 16a, 16b, 16c are carried with the production flow to the sampling point. During transport, the tracers associate with the gas phase. The gas is sampled to measure the high concentration peaks as they arrival at surface. The volume between the arrival of each tracer peak may be proportional to the inflow that occurs upstream of each tracer. The measured results may be compared with simulations to determine the inflow distribution. The system may use an iterative technique that assumes an inflow distribution, simulates the arrival time of the tracer peaks based on that assumed inflow distribution, and compares the simulated results to the measured peak arrivals. After several iterations, the method may converge on an inflow distribution that best fits the actual measured data. Additionally or alternatively tracer data collected from the gas sampling may be analysed to identify the rate of decline of the tracer concentration from each tracer location to determine a percentage of reservoir inflow from each influx zone. When a tracer is carried with the production flow to surface from the tracer source location the zones with high inflow rates flush out the tracer faster than zones with low inflow rates, thereby preserving a high concentration of tracer molecules and generating a profile with steep rates of decline. Conversely the concentration of tracer molecules in the fluid that is carried to surface from a low-performing zone becomes more diluted as it slowly enters the main flow stream and travels to the surface. Consequently, the profile of the tracer concentration presents a less steep rate of decline when compared to a high-performing zone. The data may be analysed to compare the rate of decline in tracer concentration between each monitored zone and quantitatively determines the respective relative inflow rates.

[0110] The tracer data for tracers 16a, 16b and 16c in the gas samples may be analysed to compare the rate of decline in tracer concentration between each monitored zone and quantitatively determine the respective relative inflow rates.

[0111] By modelling changes tracer concentration in the gas phase samples during initial production when the tracer concentration is high and decreasing as a function of cumulative volume and comparing the measured concentrations from samples to simulated data the percent of total inflow for each monitored zone may be identified.

[0112] By analysing the arrival pattern of tracers in gas samples and / or tracer concentration decay, it is possible to determine both qualitatively and quantitatively an influx profile of the well.

[0113] Each of the steps of collection, detection, analysis and / or interpretation of tracer data in production fluid may be considered as separate methods from one another and performed at different times and / or jurisdictions. Each of the detection, analysis and / or interpretation stages may be separate methods to the release of tracer cloud from the tracer release apparatus and / or the collection of samples. Samples of produced gas may be collected at a first time and location. The sample may be analysed to detect tracer and / or tracer data interpreted at a later time and / or different jurisdiction which is separate and distinct from the location of well and therefore the collection of the samples. The present invention in various aspects may provide information on the production of oil from a reservoir to a well comprising two or more influx zones by analysing gas samples collected from the production flow. This may allow well operators to have better knowledge of oil production and zonal contribution for each zone in the well. This may provide important information for production operations and future economic viability of the well.

[0114] The present invention relates to a method of estimating an oil flow characteristic from a hydrocarbon reservoir to a production well with two or more influx zones or influx locations to a production flow, the well comprises at least one tracer source with distinct tracer in known levels of the production well. The method comprises producing fluid in the well from the reservoir, collecting at least one gas phase sample from the produced fluid. The method comprises analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer. Based on the presence and / or concentration of the at least one tracer in the at least one sample estimating an oil flow characteristic.

[0115] Aspects of the invention may improve tracer detection limits and mitigate background noise as tracer in the gas phase samples contain less solid and liquid contaminates which could interfere with sample processing and detection.

[0116] Aspects of the invention may mitigate logistical challenges and / or sample export restrictions as gas samples do not face the same logistical challenges or restriction as liquid samples.

[0117] Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. Furthermore, relative terms such as”, “downstream” .“upstream” and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations.

[0118] The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims. Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.

Claims

Claims1. A method of estimating an oil flow characteristic from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow; wherein the well comprises at least one tracer source with distinct tracer in at least one known level of the production well, the method comprising: producing fluid in the well from the reservoir, collecting at least one gas phase sample from the produced fluid in a collecting device configured to preserve the at least one gas phase sample for later analysis; analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer; based on the presence and / or concentration of the at least one tracer in the at least one sample estimating an oil flow characteristic.

2. The method according to claim 1 wherein the at least one tracer is configured to associate with a first phase under a first condition and / or at a first location and associate with a second phase under a second condition and / or at a second location.

3. The method according to claim 1 or 2 wherein the at least one tracer is configured to associate with oil in a liquid phase at an influx zone and configured to associate with a gas phase downhole before it reaches a sampling location.

4. The method according to any preceding claim comprising collecting the at least one sample at one or more sampling times.

5. The method according to any preceding claim comprising collecting the at least one sample for later analysis onsite or offsite.

6. The method according to any preceding claim comprising collecting the at least one gas sample under pressure or at ambient pressure.

7. The method according to any preceding claim comprising collecting the at least one sample in a gas sample container selected from the group comprising sampling tube, chemical adsorption tube, isotube, PVT sample canister, bag and / or a balloon.

8. The method according to any preceding claim comprising analysing the gas samples for type and / or concentration of the at least one tracer as a function of sampling time.

9. The method according to any preceding claim comprising analysing the at least one gas phase sample for the presence and / or concentration of the at least one tracer onsite and / or in real time.

10. The method according to any preceding claim comprising extracting the at least one tracer from the gas sample to a sorbent material.

11. The method according to any preceding claim comprising collecting the at least one sample in gas sample container comprising a sorbent material configured to adsorb the at least one tracer.

12. The method according to claim 10 or 11 comprising analysing the at sorbent material for the presence and / or concentration of the at least one tracer.

13. The method according to any preceding claim wherein the at least one tracer is selected from the group comprising stable organic compounds, perfluorinated hydrocarbons, perfluoroethers, partly fluorinated compounds, perfluoro buthane (PB), perfluoro methyl cyclopentane (PMCP) and / or perfluoro methyl cyclohexane (PMCH).

14. The method according to any preceding claim comprising detecting the at least one tracers in amounts as low as 1 part per trillion volume per volume.

15. The method according to any preceding claim detecting and / or measuring the at least one tracer in the gas sample using a technique selected from the group comprising optical detection, spectrophotometric methods, spectrometric methods and / or chromatographic methods, gas chromatography, gas chromatography tandem mass spectrometry, gas chromatography-electron capture detector, mass spectrometry and / or radioactivity analysis.

16. The method according to any preceding claim comprising inducing a transient in the flow rate to create a tracer transient.

17. The method according to any preceding claim comprising estimating an oil influx profile to a producing well with two or more influx zones based on the concentration of the at least one tracer as a function of sampling time.

18. The method according to any preceding claim comprising creating a model to simulate characteristics of the flow from the reservoir to the well and comparing modelled tracer gas phase sample data to measured tracer gas phase sample data.

19. The method according to any preceding claim comprising arranging, installing, integrating and / or positioning the tracer sources in known levels of the well.

20. A system for estimating oil flow characteristics from a hydrocarbon reservoir to a production well with at least one influx zone or influx location to a production flow, the system comprising: at least one tracer source with distinct tracer configured to be installed in at least one known level of the well; at least one collection device configured to collect at least one gas sample of well fluid downstream of the at least one influx zone wherein the at least one collection device is configured to preserve the at least one gas sample for later analysis.

21. The system according to claim 20 comprise a tracer analyser for analysing the presence, type and / or concentration of the at least one tracer.

22. The system according to claim 20 or 21 comprises a processor configured to estimate or calculate an oil flow characteristic from a hydrocarbon reservoir to a production well based on the presence and / or concentration of the at least one tracer in the samples as a function of time.

23. The system according to any of claims 20 to 22 comprising a processor configured to estimate an oil influx profile based on the presence and / or concentration of the at least one tracer in the samples as a function of time.

24. The system according to any of claims 20 to 23 wherein the collection device is selected from the group comprising sampling tube, chemical adsorption tube, isotube, PVT sample canister, bag and / or a balloon.

25. The system according to any of claims 20 to 24 wherein the at least one tracer is selected from the group comprising stable organic compounds, perfluorinated hydrocarbons, perfluoroethers, partly fluorinated compounds, perfluoro buthane (PB), perfluoro methyl cyclopentane (PMCP) and / or perfluoro methyl cyclohexane (PMCH).

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