ANALYSIS OF DRILLING CUTTINGS

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefit under 35 USC § 119 (e) to U.S. Provisional Application Ser. No. 63/665,498 filed Jun. 28, 2024, entitled “Analysis of drilling cuttings,” which is incorporated herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

This invention relates to the analysis of cuttings from drilling in hydrocarbon-bearing rock formations.

BACKGROUND OF THE INVENTION

Tracers are easily identifiable substances, e.g. radioactive elements, that can be introduced into a borehole or formation and retrieved to provide information. Drilling tracers are introduced into drilling fluid and then detected in fluid that has returned to the surface; they can be used to infer information about the borehole or the drilled formation. Production tracers are injected into injector wells and retrieved from producing wells to investigate flow within the formation.

Using inter-well tracers in subsurface analysis is a well-established method for gaining insights into potential flow paths from injector wells to producer wells. This communication between wells offers a dependable way to add more detail to reservoir characterization and reduce uncertainties. The technique can provide additional insights into the remaining oil that the injected fluid didn't sweep, thus improving field development and maximizing asset value.

Traditionally, a tracer is added to injected fluid and allowed to flow through the reservoir, and then detected when it breaks through to a producer well. The tracer is typically collected with the produced fluid at the wellhead and then sent to a laboratory for analysis to confirm its presence.

Drilling a well specifically to add a tracer is not normally done because of the expense of drilling. The use of drilling tracers is therefore traditionally limited to gaining information about a well being drilled. The use of production tracers primarily offers information about the timing of tracer injection in a specific injector and its recovery in a particular producer. Unfortunately, it doesn't provide detailed spatial information about the tracer's path.

BRIEF SUMMARY OF THE DISCLOSURE

The invention more particularly includes a method of analyzing fluid flow paths in a hydrocarbon reservoir, the method comprising:

• • a) drilling a production well into the reservoir;
  • b) whilst drilling, circulating drilling fluid into the well and retrieving returned drilling fluid together with rock cuttings;
  • c) analyzing the rock cuttings for the presence of tracers.

The rock cuttings contain tracers previously injected into the reservoir through a different well. The step of analyzing rock cuttings may include identifying a well or wells from which tracers originate. Differentiable tracers may have previously been injected into respective wells.

Using this method, it may be possible to deduce fluid flow paths within the reservoir based on the receipt and analysis of tracers in rock cuttings. A substantial time may have elapsed between injection of tracers into the reservoir and drilling the production well; it is believed that tracers may remain in reservoir rock for many years, e.g. more than 5 years or as much as 50 years or more, including a period selected from at least 5, 10, 15, 20, 25, 30, 35, 40, 45, and 50 years.

Based on the information derived from this method, better informed decisions may be made about where to drill a further production well or wells, taking into account the presence and variety of tracers in cuttings from the original production well.

A tracer as used herein may be described as an infinitesimal and identifiable part of a mass that is introduced or naturally present, and that can be used to keep track of that mass. A large variety of tracers known to those of skill in the art including water tracers, oil tracers, gas tracers, stimulation tracers, specialty and proprietary tracers. Tracers are available from a variety of commercial providers including TRACERCO™, CORELAB™, NCS MULTISTAGE™ SCHLUMBERGER™ and the like. Tracers may be dyes, chemicals, nanoparticles, radioactive elements, fluorescent dyes including fluorescein, rhodamine, amino G, pyranine and the like, inorganic ions, aromatic acids, radioactive compounds, halogenated compounds including fluorocarbons, chloro- and fluorobenzoates, naphthalene sulfonates, benzoic esters, perfluorocyclohexane, sulfur hexafluoride, freons, tritiated gases, are a few of the many commercially available tracers.

Examples and various features and advantageous details thereof are explained more fully with reference to the exemplary, and therefore non-limiting, examples illustrated in the accompanying drawings and detailed in the following description. Descriptions of known starting materials and processes can be omitted so as not to unnecessarily obscure the disclosure in detail. It should be understood, however, that the detailed description and the specific examples, while indicating the preferred examples, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only those elements but can include other elements not expressly listed or inherent to such process, process, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

The term substantially, as used herein, is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder.

Additionally, any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead, these examples or illustrations are to be regarded as being described with respect to one particular example and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized encompass other examples as well as implementations and adaptations thereof which can or cannot be given therewith or elsewhere in the specification and all such examples are intended to be included within the scope of that term or terms. Language designating such non-limiting examples and illustrations includes, but is not limited to: “for example,” “for instance,” “e.g.,” “In some examples,” and the like.

Although the terms first, second, etc. can be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present inventive concept.

While preferred examples of the present inventive concept have been shown and described herein, it will be obvious to those skilled in the art that such examples are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the disclosure. It should be understood that various alternatives to the examples of the disclosure described herein can be employed in practicing the disclosure. It is intended that the following claims define the scope of the disclosure and that methods and structures within the scope of these claims and their equivalents be covered thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefits thereof may be acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram showing prior art, and two possible paths for detected tracer to have taken;

FIG. 2 is a schematic diagram showing the method according to the invention; and

FIG. 3 is a schematic diagram showing a different drilling scenario according to the invention.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

As shown in FIG. 1, which shows a known technique, the complexity of reservoirs often leads to intricate and meandering flow paths. In a reservoir 1, an injector well 4 and a producing well 3 are drilled. A tracer, which can be a substance that is easily identified chemically or includes a radioactive element, is injected into injector well 4.

Normally the injector well 4 would be created for injected water under pressure to assist recovery of hydrocarbons. When hydrocarbons are produced from the producing well 4, they are analyzed for the presence of the tracer. This can help understand the route taken by injection water and by the hydrocarbons themselves within the reservoir. This information that may be useful, for example, when deciding whether and where to drill any additional production or injection wells.

Between the wells is a fault line 2 that tracer fluid injected into the injector well 4 cannot cross. First and second theoretical potential paths for tracer fluid around the fault line 2 are identified respectively by references 5 and 6 in FIG. 1. It is not possible to determine which of the two paths the tracer has taken, or whether it has taken both.

Obviously, the representation in FIG. 1 is highly simplified but it illustrates how complex fluid flow paths can result from the characteristics of the reservoir, which can make it challenging to obtain a straightforward understanding of the flow paths. When relying solely on this method, it may be necessary to make assumptions due to the convoluted nature of fluid movement within the reservoir. To gain a more comprehensive understanding, additional techniques or technologies are sometimes needed to capture the full complexity of fluid movement in the reservoir. Often, a producer well may be drilled and found to be non-productive. If further information about fluid flow paths were available, the number of such wasteful and expensive non-productive wells may be reduced.

Of course, if additional injector wells are drilled, then this could help to alleviate the problem, but there may not be a need for additional injector wells. Alternatively, the locations of any additional injectors are chosen to achieve maximum production from existing producer wells and not to provide the best injection point for tracer chemicals to reveal information about the reservoir.

In the method according to the invention, cuttings from drilling new production wells are analyzed to expand the range of information available. By analyzing cuttings rather than produced fluids, previously injected tracers from one or more injector wells may be detected. No additional drilling or injecting operations need be carried out; instead, the cuttings from a drilling operation can simply be sent to a laboratory for analysis. If this is routinely done each time a well (either for production or injection) is drilled, then a lot of additional data about flow paths in the reservoir can be obtained, which may inform decisions about the drilling of further producing or injecting wells, and so on.

Normally, in a given reservoir, different tracers will have been injected in respective different injector wells. Therefore, cuttings may contain tracers from a number of different past injection operations. The presence and even the concentration or relative concentration of different tracers in the cuttings can provide further detail about the reservoir flow paths.

Although the amount of tracer in cuttings is less than would be recovered in a conventional operation, where the tracers are simply detected in produced fluids, the inventors have found that is it is possible to detect tracers in cuttings.

FIG. 2 shows in schematic form how the analysis of cuttings from further production wells drilled in the reservoir illustrated in FIG. 1 can be used to determine which of the two possible paths 5, 6 the tracer has taken around the fault line. A second production well 7 is drilled to one side of the first production well 3. No tracer is detected in the cuttings from the second production well 7, and this supports a conclusion that no tracer has flowed along the first theoretical flow path 5 and therefore that reservoir fluids cannot or do not take this route from the location of the injector well 4.

A third production well 8 is then drilled on the other side of the first production well 3. Tracer originating at the injector well 4 is detected in the cuttings from drilling the second production well 8, supporting the conclusion that tracer chemicals, and therefore reservoir fluids, take the second potential flow path 6 around the fault 2 from the injector well 4.

By analyzing cuttings, therefore, new information is provided that challenges the validity of first path 5 as the connection between the producer and injector and strongly suggests that second path 6 is the most likely communication route.

This information could, for example, support a decision to drill further production wells in the region of the second flow path 6 rather than on the other side of the fault line 2. Obviously, this example is highly simplified and many other factors would be taken into account in decision making.

It can be seen that a large amount of useful data could be obtained from being able to detect a variety of tracers from different past injection procedures when each new production well is drilled.

This approach complements traditional well drilling and relies on information derived from in-depth analysis of reservoir cuttings generated during the drilling process. These cuttings are gathered and subjected to tracer analysis, similar to fluid samples. However, this analysis adds valuable spatial information and significantly reduces uncertainty when it comes to understanding the flow paths within the reservoir.

The advantages of this method include its simplicity and economy. It may eliminate the need for additional tracer injections since it relies on collecting cuttings.

The inventor has developed and tested a procedure for tracer recovery from cuttings. Extensive testing of various methods for tracer recovery from cuttings has been carried out, and the procedures have been optimized to enhance the chances of successful recovery of tracers.

The elements of the tracer detecting process include cuttings handling, cleaning procedures and imbibition time. Thorough managing these aspects, the recovery procedure has not only successfully detected the tracers but has also demonstrated the feasibility and effectiveness of this method.

Another scenario is depicted in FIG. 3. This is a typical situation where a producing well 20 is located at the crest of a subterranean hydrocarbon field, shown by depth contours 21. The production well 20 is supported by two down-flank water injector wells 22, 23. A potential fault 24 within the field complicates development planning, as the fault's conductivity and its impact on sweep efficiency are unknown.

A new horizontal producer 25 has been drilled across the fault 24 and is found to have intersected zones 26, 27 (shaded areas in FIG. 3) that have been flooded by the injectors 22, 23. Production is therefore not possible from the new horizonal producer 25. However, without analysing cuttings, all that is known is that the new producer 25 is flooded and can't be used.

Cuttings collected while drilling the producer 25 are sent for analysis. The cuttings are analysed based on where in the producer 25 they came from. The analysis results show that a first flooded section 28 is attributed to injector 22, while a second flooded section 29 is flooded by injector 23.

This information is significantly more valuable than relying solely on pressure or saturation data, as it not only confirms the presence of flooding but also attributes it to specific injectors. Without cuttings analysis, such insight would be incomplete, as it would only indicate that the well is flooded without identifying which injector is responsible. Moreover, the fact that the flooded zones are separated by the fault provides critical information about the fault's behavior. This insight is key for optimizing field development and improving recovery strategies.

The horizontal producer 25 cannot be used since it is flooded, but based on the information derived from its cuttings, a strategy for drilling new injectors to enhance production from the original producer 20 can be developed. It would be more beneficial to drill a new injector at location 30 west of the fault, rather than drill an injector at location 31 located east of the fault. The presence of the fault would hinder support from an injector at 31, reducing its efficiency. In contrast, an injector at 30 would have better connectivity and provide more effective support to the producer 20.

Example

An injector well was drilled by the applicant in 2016 and tracer injected in 2018. A nearby well was drilled in 2021 and the cuttings analyzed. Tracer from the 2016 well was located.

Further experimental analysis of rock cuttings to find tracers and deduce fluid pathways are planned.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as a additional embodiments of the present invention.

Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents.

REFERENCES

All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience:

• • 1. U.S. Pat. No. 4,099,565-Single well tracer method to evaluate enhanced recovery.
  • 2. U.S. Pat. No. 4,168,746-Single well surfactant test to evaluate surfactant floods using multi tracer.
  • 3. U.S. Pat. No. 4,213,762-Determination of chromate ion in drilling mud filtrates.
  • 4. U.S. Pat. No. 4,743,761-Natural tracer for secondary recovery water injection process.
  • 5. U.S. Pat. No. 4,857,234-Method for making a partitioning radioactive tracer.
  • 6. U.S. Pat. No. 4,876,449-Reservoir evaluation using partitioning tracer.
  • 7. U.S. Pat. No. 5,246,861-Use of nonradioactive complex metal anion as tracer in subterranean reservoirs.
  • 8. U.S. Pat. No. 11,286,771-In-situ surfactant retention evaluation using single well chemical tracer tests.
  • 9. U.S. Pat. No. 11,002,722-Time-series geochemistry in unconventional plays.
  • 10. US-2022-0391998-Fingerprinting and Machine Learning for Production Predictions.