Wax tracers

Abstract

A method for monitoring precipitation of a wax component in a hydrocarbon fluid stream i) using a labelled wax introduced in a fluid transport system at one in-flow point and measuring its absolute or relative concentration at one out-flow point is provided. A method for generating a labelled wax, and the use of a labelled wax is also provided.

Claims

1. A method for monitoring precipitation of at least one wax component from a hydrocarbon-containing fluid stream flowing through a fluid transport system having at least one in-flow point and at least one out-flow point, the method comprising: a) taking a sample of the hydrocarbon-containing fluid stream; b) analyzing the sample of the hydrocarbon-containing fluid; c) identifying at least one of a group consisting of a structure and molecular weight of at least one wax component in the sample of the hydrocarbon-containing fluid; d) selecting or generating at least one labelled wax based upon the structure or molecular weight of the at least one wax component identified in step c), wherein the selected or generated at least one labeled wax is labeled with either an isotope label or with a covalently attached label; i) introducing the at least one labelled wax selected or generated in step d) into the hydrocarbon-containing fluid stream at the at least one in-flow point; and ii) measuring a relative or absolute concentration of the at least one labelled wax in at least one sample taken at the at least one out-flow point.

2. The method of claim 1, wherein step a) comprises taking a sample of the hydrocarbon-containing fluid stream at a point selected from at least one of a group consisting of an in-flow point of the fluid transport system, an out-flow point of the fluid transport system, another point on the fluid transport system and at a production point within a formation during at least one of a group consisting of production, development and exploration.

3. The method of claim 1, wherein the at least one labelled wax is to precipitate alongside the at least one wax component precipitating from the hydrocarbon-containing fluid stream.

4. The method of claim 1, wherein the structure of at least one wax component is identified in step c) and the at least one labelled wax is selected or generated in step d) to have a structure comprising the structure of the at least one wax component identified in step c) and at least one label.

5. The method of claim 1, further comprising undertaking at least one wax mitigation measure when the relative or absolute concentration measured in step ii) falls below a threshold value.

6. The method of claim 5, wherein the at least one wax mitigation measure comprises at least one of a group consisting of starting or increasing an addition of at least one de-waxing component to the hydrocarbon-containing fluid stream, mechanically de-waxing at least a part of the fluid transport system, and thermally de-waxing at least a part of the fluid-transport system.

7. The method of claim 1, further comprising undertaking at least one wax mitigation measure when an integral of a curve of relative or absolute concentration measured in step ii) against time for a predetermined period falls below a threshold value.

8. The method of claim 1, wherein step i) is carried out one of periodically and continuously.

9. The method of claim 1, wherein step ii) is carried out one of periodically and continuously.

10. The method of claim 1, wherein step i) is carried out periodically for at least 1 year following an event selected from at least one of a group consisting of a change or partial change in source of the hydrocarbon-containing fluid stream, at least one from a group consisting of the addition, removal and replacement of at least one element of the fluid transport system, at least one from the group consisting of an addition, removal and change in concentration of at least one additive introduced into the hydrocarbon-containing fluid stream, and a change in conditions of at least one from a group consisting of temperature and pressure at at least one point on the fluid transport system.

11. The method of claim 1, wherein the fluid transport system comprises at least one from a group consisting of a pipeline, a valve, a choke, a separator, filters, mixers, joints, thermal expansion joints, and tie-inns.

12. The method of claim 1, wherein the at least one labelled wax and at least one labelled non-precipitating component are introduced in step i) at a known relative concentration and step ii) comprises measuring the relative concentration of the at least one labelled wax and the at least one labelled non-precipitating component in the at least one sample.

13. The method of claim 1, wherein the at least one labelled wax is labelled by means of a radioactive isotope selected from at least one of a group consisting of .sup.3H, .sup.14C, .sup.35S, .sup.32P, .sup.125I, .sup.131I and .sup.82Br.

14. The method of claim 1, wherein the at least one labelled wax is labelled by means of at least one of a group consisting of a radioactive isotope, a non-radioactive heavy isotope selected from at least one from a group consisting of 2.sup.2H, .sup.13C, .sup.15N, .sup.18O and .sup.34S and a covalently attached fluorophore.

15. The method of claim 1, wherein the precipitation of the at least one wax component from a hydrocarbon-containing fluid stream flowing through a fluid transport system having at least one in-flow point and at least one out-flow point is monitored by monitoring precipitation of the at least one labelled wax.

16. A method for the generation of at least one labelled wax comprising: a) taking a sample of a hydrocarbon-containing fluid stream; b) analyzing the sample of the hydrocarbon-containing fluid; c) identifying at least one of a group consisting of a structure and molecular weight of at least one wax component in the sample of the hydrocarbon-containing fluid; d) selecting a wax based upon the structure or molecular weight of the at least one wax component identified in step c); and e) covalently or isotopically modifying the selected wax with at least one label.

17. The method of claim 16, wherein step a) comprises taking a sample of the hydrocarbon-containing fluid stream at a point selected from at least one of a group consisting of an in-flow point of a fluid transport system, an out-flow point of a fluid transport system, another point of a fluid transport system, and at a production point within a formation during at least one from a group consisting of production, development and exploration.

Description

BRIEF SUMMARY OF THE FIGURES

(1) FIG. 1 shows examples of molecular classes which can be used as precursors for labelling operations.

(2) FIG. 2 shows an outline of a test apparatus suitable for testing and validation of potential labelled waxes (tracers).

(3) FIG. 3: shows various possible methods for labelling an example wax molecule. 1. Is the unlabeled wax molecule, 2. to 7. represent the molecule with various labels: 2. tritium-labeled, 3. .sup.14C-labeled, 4. .sup.131I-labeled, 5. .sup.13C-substituted, 6. deuterium-substituted and 7. Functional group attached.

(4) FIG. 4: shows one potential layout of a production system where it is suggested that wax tracers are injected through a chemicals injection line to the wellhead or tie-in junction. By monitoring the traces produced to onshore facilities or to another offshore installation the initiation and magnitude of the waxing can then be monitored. In addition to the transport lines wax tracers can be used to monitor deposition in process equipment.

(5) The markings in FIG. 4 are as follows: 1Riser 2Transport pipeline (fluid transport system) 3Tracer injection line. 4Production well. 5Well/head. 6Multiphase separator. 7Analysis Point. 8Reservoir section 1. 9Reservoir section 2. 10Sealing fault.

(6) FIG. 5a. shows a sketch of wax tracer pulse injection system.

(7) FIG. 5b. shows a sketch of wax tracer injection system for continuous constant concentration injection.

(8) FIG. 5c. shows a sketch of wax tracer injection system for continuous dissolution of preformed wax precipitate containing wax tracer molecules with detectors for continuous logging of injected tracer concentration.

EXAMPLES

Example 1Study of Wax Deposition

(9) Deposition of waxy components is studied in dynamic flooding experiments in the laboratory where wax-containing condensates are pumped through steel tubes packed with steel wool to increase the contact surface. Deposition of gamma emitting wax tracers are detected directly on the outside of the steel tubing with a gamma detector. Wax molecules labeled with beta-emitting tracers or with fluorescent labels are analysed in the collected fluid at the exit of the flow rig. Two procedures are applied: 1. The liquid is pumped through the equipment only once, i.e. the internal walls of the flow loop are continuously contacted with fresh wax-containing condensate at constant concentration. 2. The condensate is recycled without any solute addition. In these experiments parameters are temperature, wax type and concentration and tracer type. A principle sketch is shown in FIG. 2.