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Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017
Chapter
3 – P ressure Transient Analysis (PTA)- p96/743
Beyond the usual cleaning of irrelevant data and the correction of load errors, the main
challenge will be to end up with at least one coherent, synchronized set of rate and pressure
data. To get there the engineer may have to perform the following tasks:
Get all data acquired electronically to the same reference time.
If not already loaded, create the rate history graphically by identifying the pressure breaks
and get the rate values from the well test report. Use a facility to automatically identify the
shutin periods and automatically correct the production history from volumes to rates.
Refine the production history, when the time sampling of rate measurements is too crude.
Conversely, if the production history goes into useless details, simplify the rate history to
reduce the CPU time required to run the models.
Fig. 3.E.7 – Editing data:
Pressure and production history adjustment
3.E.5
Extraction and diagnostic
Once the data have been synchronized and validated, the analysis itself will start. The
engineer will focus on one or several gauges, one or several flow periods, and will create the
appropriate diagnostic tools, starting with the loglog and the semilog plots. When several
gauges are used, they will be overlaid. When several production and/or shutin periods are
extracted, they will be rate-normalized, then overlaid. In the case of Saphir, this extraction is
followed by an automatic positioning of a horizontal line for IARF on the Bourdet derivative and
a unit slope line for pure wellbore storage on both pressure and the Bourdet derivative. This
positioning is set by a relatively simple filtration, the main goal being to put these lines in the
same ‘range’ as the data. Surprisingly, this sort of processing works quite well in the case of
simple responses, giving an instantaneous estimate of the wellbore storage and permeability-
thickness product. In case of complex behavior, the software may have selected the wrong
level of the derivative for IARF and or the wrong unit slope for wellbore storage. The
interpretation engineer will then interactively move the two straight lines in order to properly
position these flow regimes.