WHAT YOU NEED TO KNOW BEFORE YOU START
This page covers a brief overview of computer aided log evaluation,
sometimes erroneously called computer processes interpretation
software (CPI). Computer software can analyze, process, evaluate,
get answers – but it cannot interpret. That’s your job!
The interconnecting links in the system are its most important feature. Good communication must exist, along with mutual trust and understanding, between the "user" (the engineer, geologist or geophysicist) and the "doer" (the petrophysicist). The analyst in turn, must effectively communicate with the computer hardware-software package and staff.
A good system must be built around a team concept, consisting of the lead or senior petrophysicist, a junior or trainee analyst, up to two technicians, and possibly a clerk/technologist. Some of these people are shared or "float" to projects as needed.
The senior analyst is responsible for project definition, parameter and method selection, difficult editing, work scheduling and organization, review of intermediate and final results, presentation and discussion of final results with the end-user, and training and work allocation of subordinates. He must have a thorough knowledge of log analysis methods, and be aware of all the available features on the hardware / software package. He can run the package effectively after a few days exposure to it and can modify programs to suit special cases or local requirements.
The more junior members of the team run the package under the direction of the analyst. and perform the many clerical tasks involved in organizing and filing large volumes of data. These people must be keen and adept in the use of computers.
Log analysis should be performed on a definable zone - not on an entire well at once. As many zones as needed are run to cover all potential pay sections.
The entire well may be analyzed, but as a series of discrete zones. A run control sheet is used to describe the zones to analyze, the data available, the computation method, and parameters required, as well as a brief well history to aid the analyst. The well history is also annotated on the final results to aid discussion and understanding of the log analysis by others.
On large projects, a group of 5 to 10 related zones, preferably cored and tested, will be picked, digitized, and computed as a "batch". These are reviewed, parameters adjusted as needed, recomputed, reviewed again and eventually finalized. In the earlier stages of a large project, the batches consist of those zones with the most core and DST data available. These zones are used to calibrate log analysis parameters before un-cored zones are analyzed. The organization of this procedure and the data bases required are illustrated in the block diagram below.
These stages may seem simple, even trivial or obvious, but clear definitions benefit the end-user and the analytical team, not to mention management, who may have no idea how petrophysics is really done. Large projects or continuous, on-going projects slow down if the job stream or data structure is unorganized or chaotic.
The two feedback loops shown above indicate that successive re-runs to optimize methods or parameters are easy, rapid, normal, and probably necessary.
This is the key to satisfying both the technician and the professional analyst, because individual zones are usually finished completely in just a few elapsed hours instead of days or weeks. A reasonable number of zones (5-20) may be interleaved, so that different functions are performed on different zones. This is a natural outcome of the variable number of times the zone has to be re-computed.
In smaller organizations, the analysis team may be one person, and in some instances, the team and the end-user may be the same person. This does not change the need to organize and review data and results.
organizations use a dispersed or distributed systems approach,
in which the end-user, or their technical staff, do their own
log analysis. This may be successful if training and standards
are excellent, and specialists are available for certain jobs
and for training.
EXAMPLE 3: Oil SAND - unususal fluid distribution
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