Chemistry: analytical and immunological testing – Geochemical – geological – or geothermal exploration – Using chemical tracers
Reexamination Certificate
1999-01-07
2001-12-18
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Geochemical, geological, or geothermal exploration
Using chemical tracers
C436S029000, C436S056000, C436S060000
Reexamination Certificate
active
06331436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally directed to the use of organic compounds as tracers in monitoring the flow of fluids and in particular heavy oil. In one embodiment the flow of heavy oil in a subterranean formation is monitored and in another embodiment the flow of heavy oil through a tank and pipe system is monitored. In yet a third embodiment the flow of oil from different zones in a producing well may be monitored.
2. Background
Tracers are used in the petroleum industry in order to track fluid movement and monitor the changes in flow and composition in subterranean formations. The monitoring of the flow through a formation is particularly important in managing and maximizing production during thermal recovery operations. Tracers may be added to either the water/brine phase or the steam that is injected into the formation through an injection well. Examples include halide salts, boron salts, silicates, and other inorganic and organic water soluble salts. Oil soluble tracers may be injected as part of a “slug” of oil in an injection well. Examples of oil soluble tracers include oil soluble compounds of transition or rare earth metals or highly fluorescent compounds. The principle problem with the use of such compounds is that the technology used to detect the presence of these compounds in samples, (i.e. atomic absorption, atomic emission, ultra-sensitive spectrofluorometry, Internally Coupled Plasma-Mass Spectroscopy (ICP-MS), etc.) is expensive, not suitable for field use and requires highly trained technicians.
Radio-isotopically labeled water soluble or oil soluble compounds have also been used a tracer compounds. These tracers are injected into the subterranean formation using an injection well in a similar manner as the corresponding non-radioactive tracers. The flow of oil in the subterranean formation is determined by monitoring samples taken from a production well and determining the concentration of radioisotope is determined in each sample. From such data, a time verses concentration curve provides information as to the flow characteristics of the subterranean formation. Examples of radio-isotopically labeled tracers include a
131
I labeled iodoethanol,
59
Fe labeled dicyclopentadienyl iron (II) (i.e.
59
Fe-ferrocene) amongst others.
Although the use of radio-isotopically labeled tracers is very sensitive to low concentrations of the tracer in the sample, there are several problems with the use of these tracers. First is the handling and environmental concerns of using and detecting a radio-isotope. Often this requires specialized training and permits from governmental authorities. Cost is another concern since radio-isotopically labeled compounds are expensive and they are not typically recoverable from the produced fluids. Further, the injection of radio-isotopically labeled tracers “contaminates” the entire formation with a radio-isotope which alters the natural isotopic composition of the produced fluids. Such contamination may interfere with the scientific analysis of the produced fluid's characteristics. In particular, the use of radio-isotopically labeled tracers may interfere in the radio isotope dating of the formation. Finally, and not the least of importance, the use of a radio-isotope labeled tracer may be limited by the unduly short or excessively long half life of the radio-isotope.
Much of the work in tracer compounds for thermal recovery operations has focused on water or brine soluble tracers since such compounds can be easily added to the water, brine or steam injected into the formation during a water injection, steam flood, or other thermal recovery operations. Examples of such tracers may be found in U.S. Pat. No. 5,246,860 which discloses the use of carboxylic, and sulfonic acids and their salts as suitable tracers. Although oil soluble tracers are disclosed, they are limited to aniline and pyridine compounds that upon addition of acid form water soluble salts.
Despite the above developments in tracer technology, there exists a continuing need for oil soluble tracers, especially those that can be used in monitoring the flow of heavy oil during a steam flood or other thermal recovery process.
SUMMARY OF THE INVENTION
The present invention is generally directed to a process of monitoring the flow of a fluid from a first point to a second point, the first point being in fluid communication with the second point. The process includes injecting a fluid soluble tracer into the fluid to be traced at the first point and analyzing at least one sample from the second point for the tracer. The tracer may include a fluid soluble organic compound having more than 25 carbons that: is compatible with the characteristics of the fluid; is thermally and chemically stable under the conditions encountered between the first point and the second point and is present in a concentration such that it can be detected in the sample from the second point. It is preferred that the tracer be selected from long chain hydrocarbons having a primary chain of more that 25 carbon atoms, and more preferably that the tracer be a saturated hydrocarbon.
In one exemplary embodiment, the process may be used to monitor the flow of oil or other subterranean fluids in a subterranean formation. In another embodiment, the process may be used to monitor the flow of fluid through a system of tanks and pipes.
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Stone, T., Perkins, E., and Schmidt, T., “Tracers in Analysis of Steamfloods,” Paper No. 20, Third Technical Meeting of the South Saskatchewan Section, CIM, Regina, Canada, Sep. 1989.
Perkins, E.H., Young, B.K., Gunter, W.C., and Turner, J.C., “Evaluation of In-Situ Geochemical Tracers and Their Implication for Production at a South Midway Sunset Heavy Oil Reservoir,” SPE#24946, presented at the SPE 67th Annual Technical Conf., Washington, DC, Oct. 4-7, 1992.
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Skauge, A., Aanonsen, S.I., and Graue, A., “Dynamic Fluid Saturation Profiles in the Analysis of Surfactant Flooding Core Displacement,” SPE/DOE 17347, Sixth Symposium on Enhanced Oil Recovery, Tulsa, OK (Apr. 1988) pp. 289-302.
Kimber Kevin D.
Richardson William C.
Gakh Yelena
Howrey Simon Arnold & White
Reinisch Morris N.
Texaco Inc.
Warden Jill
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