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Chapte
r 4 – R ate Transient Analysis (RTA)- p150/743
4.E
Modern RTA methodology
Modern Rate Transient Analysis is based on the use of PC based RTA software products. The
key for any modern software is to combine user friendliness to a powerful technical kernel,
requiring both analytical and numerical capabilities. In terms of methodology, the central
diagnostic tools are the Blasingame and loglog plots, which are used whenever such a
diagnostic is possible. However, because of the very scattered nature of production data, the
ultimate diagnostic tool will often be the history plot, where the coherence of the model and
the data, in terms of simulated pressures, rates and cumulative productions, will be the final
decision tool for the interpretation engineer.
Once the interpretation is initialized and production data loaded, the first task will be to extract
the interval of time on which the analysis will be performed. If the pressures are not available,
only the ‘old’ tools can be used. If both rates and pressures are available, the interpretation
will be performed with the four main diagnostic tools. The interpretation engineer can select
one or several analytical and/or numerical models, set their parameters and generate these
models for comparison with the actual data. For models that are believed applicable, the
engineers can refine the model leading parameters, either manually or by using nonlinear
regression.
Once this is finalized, the engineer may use the model(s) to forecast future production by
defining a scenario of producing pressures. The user can then run a sensitivity analysis on a
selection of the model parameters.
The path described is the default path when all is well. In reality, for complex problems, it
becomes a trial-and-error process where the interpretation engineer may decide to go back
and forth as needed when part of the process is unsatisfactory.