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Chapter
3 – P ressure Transient Analysis (PTA)- p92/743
3.E
Modern PTA methodology
Modern Pressure Transient Analysis is based on the use of PC based PTA software products.
The key for any modern software is to combine user friendliness and a powerful technical
kernel, with both analytical and numerical capabilities. In terms of methodology, the central
diagnostic tool is the loglog plot, showing both pressure and the Bourdet derivative used for
the diagnostics and the match with the selected model(s). The sections below describe the
typical path of today’s Pressure Transient Analysis. It was our understanding of what this
typical path should be that led us to implement this in Saphir.
Once the interpretation is initialized the first task is to get a coherent and representative set of
rate and pressure data. This includes loading the data, quality check and validation and editing
to prepare for analysis. One or several periods of interests, typically buildups, will then be
extracted and the diagnostic plot created and the data diagnosed. The interpretation engineer
can select one or several candidate analytical and/or numerical models, set their parameters
and generate these models. For candidate models that are retained, the engineer can refine
the parameters, either manually or using nonlinear regression. Once the model parameters are
finalized, the user may assess the sensitivity and/or cross-correlations of the parameters using
confidence intervals from the nonlinear regression and run sensitivity analysis. Finally, a report
is issued.
The path above is the default path when all goes well. In reality, for complex problems, it may
be a trial-and-error process where the interpretation engineer may decide to go backwards
before continuing forward again when a segment of the process is not satisfactory.
3.E.1
Initialization
The data and the operation need first to be reference in time and spavce. The interpretation
engineer must then input information required to identify the test and select the main options
that will set up the interpretation process: the type of test (standard, interference). The
engineer may start with a standard analysis, nonlinear numerical, shale gas or coalbed
methane (CBM), multilayer analytical or linear numerical, or a formation tester type of
analysis. The final input will be the parameters that are assumed to be known which are
required to calculate the interpretation results: porosity, net drained vertical thickness, well
radius, etc.
Fig. 3.E.1 – Time and Spatial references and General conditions