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Production logging application tables
This topic page provides an extensive set of tables intended to aid in the practical application of production-logging technology.
For a given problem, the reader is guided first in the selection of the set of logging tools most appropriate. Next, suggestions are given on the proper procedure for each tool’s use. This is an important part of the guidance, because the way logging records are obtained is often the most important part of the operation. Finally, the user is provided with comments regarding what the records should show relative to the problem. Recognition of expected results is equally important because irrelevant features on a log can easily prevent its proper interpretation. The tables are independent of the preceding body of the text and presume that the user lacks detailed knowledge of the subject.
The tables are unique to the literature in their ability to provide the user with detailed guidance without the investment of extensive search time. This feature is a consequence of the indexing approach to the information in the tables. The first level in the classification system is the nature of the well and the type of completion in which the tools are to be run. This environmental factor is called the Well Category. The tools that are best for one type of completion may be completely inappropriate for another type. For a given Well Category, the second level is the type of problem of interest to the user. This level is called Problem Type. Its identification leads to the final or third level in the classification—namely, to a table of tools appropriate to the specific well category and problem type. This final table provides the information listed above. Such an approach leads to much duplication of material, but is the one most beneficial to the user. Available publications attempt the classification on the basis of problem type alone, but this approach leads to so many disclaimers "for this situation and for that situation" that the result is confusion rather than guidance.
Function and utilization of tables
To make use of the application tables, one enters the compilation sequentially through two indexing tables, identified as Table A1: Well Category and Table A2: Problem Type. Having selected a category number from Table A1 (Level 1), the user than locates this number in Table A2 (Level 2), where a listing of general problem types is associated with each category number. Each problem type is identified by its index number, made up of a category number followed by a capital letter. For example, the designation 1A identifies a well still being drilled (well category) but experiencing problems of pipe sticking (pipe manipulation) or cross-sectional constriction (problem type). Having selected an index number from Table A2, the reader next locates the third-level table having this number/letter designation. This final table subdivides the general problem into more specific problems (where appropriate) and provides a listing of recommended logging tools along with suggestions concerning their proper use and comments on what one should expect to see in the records from each tool. The tools are listed in the order of their likelihood to resolve the reasons for a particular problem; consequently, tool exclusion for a particular job should start at the bottom of the list and work upward.
The well category, Table A1, cannot include all possible combinations of tubing placement relative to casing. The user may therefore not find a single category that describes completely an unusual completion. Instead, the completion may have at certain locations features common to one particular listing, whereas, at other locations, the features may coincide with a different listing. In such a case, the user will need to digest the contents of several tool-selection tables to devise a tool string appropriate to the completion.
A general comment is in order relative to tool selection. Slickline or downhole-memory logging tools have evolved to the point that multiple traces can be recorded on a single pass. This gives the ability to record traces from depth-control sensors, such as a collar locator and a gamma-ray tool, simultaneously with traces from production-logging sensors. The previously limited quality in depth control has therefore been eliminated. Furthermore, sample rates can be set sufficiently high (up to 5 samples per second) so that the tools produce traces with a quality equal to that from electric-line surveys. In fact, the newer sensors on slickline strings often provide better traces. A corresponding improvement in surface interrogation and processing hardware now makes it possible to prepare a log from a slickline string within a few hours after tool retrieval. Memory tools now have practically all the advantages of electric-line tools with the added potential for safer and less-expensive operation.
Despite the extensive nature of the tables, their primary function is to provide realistic information on the selection of logging tools for a particular environment and a specific problem. The tables cannot make the user proficient in the very important task of interpretation. Moreover, computer software cannot do this either; intervention by an expert analyst is still required to ensure correct interpretation. The user should not hesitate to seek such intervention, preferably from experts other than employees of the logging company involved.
The two classification Tables A1 and A2 are used sequentially to navigate the extensive set of tables devoted to tool selection. Table A1 is used to select a category number best describing the type of well to be logged. This numeral is then entered in Table A2 and associated with the capital letter best describing the type of problem to be resolved. The resulting Index Number identifies one of the Tool-Selection Tables . This final table provides the user with the information necessary to plan and conduct the logging operation.
These guidance tables list recommended logging tools in order of general effectiveness, giving comments regarding procedures for tool use and indicating the normal features that should appear on the log traces. Each table is identified by an index code made up of a number and a capital letter, such as 2C. A specific index code is obtained through the use of Tables A1 and A2. Each tool-selection table deals with a particular problem area for a particular well configuration.