Method for extracting downhole flow profiles from tracer flowback transients

1. A method of estimating an influx profile for at least one well fluid to a producing petroleum well with two or more influx zones or influx locations to a production flow,

wherein the well comprises tracer sources with distinct tracer materials in known levels of the well, at least one of said tracer sources arranged downstream and exposed to the fluids in at least one of said influx zones,

wherein each said tracer source has an even release rate to said well fluid,

wherein one or more of the tracer sources is provided in one or more delay chambers for ventilating out fluid with leaked tracer material at a time constant which is significantly longer than the diffusion rate from the tracer source to the well fluid,

wherein the method comprises:

providing samples, the samples collected from the production flow at a location downstream of the tracer sources during a time period in which the tracer transient is detectable at the downstream location;

analysing said samples for concentration and type of tracer material from said possible tracer sources as a function of sampling time or cumulative produced volume; and

based on said measured concentrations and their sampling time or cumulative produced volume, calculating said influx volumes.

2. The method according to claim 1 , further comprising using the calculated influx volumes as parameters for controlling the production flow or for characterizing the reservoir.

3. The method according to claim 1 , wherein the analysis of tracer materials in the samples is conducted generally after the sampling is conducted at one or more of said sampling times.

4. The method according to claim 1 , wherein the analysis of tracer materials in the samples is conducted generally on site, immediately after said sampling conducted at said one or more of said sampling times.

5. The method according to claim 1 , wherein said influx profile comprises two or more influx rates in two or more corresponding influx zones or influx locations.

6. A method of collecting samples for use in estimating an influx profile for at least one well fluid to a producing petroleum well with two or more influx zones or influx locations to a production flow, the method comprising:

providing tracer sources with distinct tracer materials in known levels of the well, at least one of said tracer sources arranged downstream and exposed to the fluids in at least one of said influx zones,

wherein each said tracer source has an even release rate to said well fluid,

wherein one or more of the tracer sources is provided in one or more delay chambers for ventilating out fluid with leaked tracer material at a time constant which is significantly longer than the diffusion rate from the tracer source to the well fluid, and

wherein the method further comprises:

inducing a transient in the production rate of the production flow, thereby changing the local exposure times of the tracer sources to the fluid in the delay chambers to create a tracer transient; and

collecting samples at a location downstream of the tracer sources after inducing the transient, during a time period in which the tracer transient is detectable at the downstream location.

7. The method according to claim 6 , comprising collecting samples before the step of inducing a transient in the production rate during a steady state of the production flow, and analysing samples for concentration and type of tracer material from said possible tracer sources.

8. The method according to claim 6 , wherein said transient in said production rate is induced generally by shutting down said production flow.

9. The method according to claim 8 , wherein said transient in said production rate is induced generally by shutting down topside at a first instant, to cause local accumulation of said tracer material near said tracer sources, and by later increasing the production rate by opening said production flow at a desired known instant.

10. The method according to claim 6 , wherein said transient in said production rate is induced locally by shutting down one or more of said local influx rates.

11. The method according to claim 6 , wherein an otherwise naturally or technically occurring transient in the production rate is utilised as said transient in the production rate.

12. A method of estimating an influx profile for at least one well fluid to a producing petroleum well with two or more influx zones or influx locations to a production flow, the method comprising:

providing tracer sources with distinct tracer materials in known levels of the well, at least one of said tracer sources arranged downstream and exposed to the fluids in at least one of said influx zones,

wherein each said tracer source has an even release rate to said well fluid,

wherein one or more of the tracer sources is provided in one or more delay chambers for ventilating out fluid with leaked tracer material at a time constant which is significantly longer than the diffusion rate from the tracer source to the well fluid, and

wherein the method further comprises:

inducing a transient in the production rate of the production flow, thereby changing the local exposure times of the tracer sources to the fluid in the delay chambers to create a tracer transient;

collecting samples at a location downstream of the tracer sources after inducing the transient, during a time period in which the tracer transient is detectable at the downstream location;

analysing said samples for concentration and type of tracer material from said possible tracer sources as a function of sampling time or cumulative produced volume; and

based on measured concentrations and their sampling time or cumulative produced volume, calculating said influx volumes.

13. A system for estimating an influx profile for at least one well fluid to a producing petroleum well with two or more influx zones or influx locations to a production flow, the system comprising:

tracer sources with distinct tracer materials arranged in known levels of the well, at least one of said tracer sources arranged downstream and exposed to the fluids in at least one of said influx zones, wherein each said tracer source has an even release rate to said well fluid, and wherein one or more of the tracer sources is provided in one or more delay chambers for ventilating out fluid with leaked tracer material at a time constant which is significantly longer than the diffusion rate from the tracer source to the well fluid; and

a valve arranged in said production flow configured for inducing a transient in the production rate of the production flow, thereby changing the local exposure times of the tracer sources to the fluid.

14. The system according to claim 13 , wherein the one or more delay chambers comprises one or more apertures to the fluid flow in a central pipe.

15. The system according to claim 14 , wherein the one or more delay chambers is arranged to conduct its influx fluids to pass from a local borehole wall, past said local tracer source, and exit through said one or more apertures to said central pipe.

16. The system according to claim 15 , wherein the one or more delay chambers is constituted as a completion component of the well for fitting into a completion pipe, and wherein said one or more tracer source is arranged in an annular space formed between said completion pipe and the borehole wall.