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Time Depth Curves - a complete suit
I'm very specialized in achieving time-depth curves, in other words, the seismic to well correlation. I consider this a very important step in Petroleum Exploration. In 15 years, I have defined more then 400 TxD curves of Petrobras wells. At the very beginning, I've developed a methodology to extrapolate sonic profiles to surface. In this procedure, one may find in detail in third green box above (SONIC EXTRAPOLATION), it is possible to extrapolate the sonic profile to surface without any geological/geophysical marker and with no velocity surveys. This became important when working in a specific area in Reconcavo Basin, that matched the phrase before. After developing shift-drift methodology (1st green box above) the sonic extrapolation methodology became unusual to me, but still there is a chance to apply this procedure in Exploratory Frontier Basins. Geologist Pedro Zalan mentioned at one technical meeting: "Adauto's shift-drift methodology configure the best seismic to well correlation in use in Petrobras". All my experience in this task may be found in the TxD suit: a group of 4 tools nominated Poroden, Editason, TvdShift and SeisSint, hereafter discussed.
Poroden is a tool based in my paper presented at 1999 SBGf International Congress. In this paper, linked above as Gardner-Wyllie methodology, it is presented porosity and density computations based on sonic profiles. This tool was developed to support basin analysis studies mainly focusing the compaction curves of several lithotypes of Reconcavo Basin. Those studies were initially supervised by Geologist Luiz Felipe Carvalho Coutinho, from Petrobras, who extended and applied this methodology to input his basin modeling block in order to obtain the complete petroleum mass balance of Reconcavo Basin. This was the purpose of his doctoral thesis developed at the Univertity of Paris VI, France. Mixing Gardner(density) and Willie (porosity) equations we reached best matches in these studies.
Editason is a graphical tool to edit sonic profiles: it is possible to edit based on anomalous sonic values and/or anomalous well caliper values. This is important to prevent bad time-depth curves.
TVDShift ia a tool to build the time-depth curve based on sonic profile: there is a complete step to extrapolate non recorded zones and to integrate recorded zone.
SeisSint is the synthetic seismogram. I believe the way it was developed is unique and the final result is very good. In the algorithm there are unusual steps trying to make the synthetic derived from transit times and densities similar to a seismic trace: the final result is a synthetic trace quite close to the seismic trace. Amplitude, phase and frequency matches very well. Here Poroden plays an important task, because in general the use of sonic densities to build synthetic seismogram culminates in better seismic to well correlation. Rhob profiles are very sensitive to well wall rugosities, implying bad readings. Also in general Rhob are limited profile runs, not covering all well extension recorded by sonic profile.
The shift-drift methodology may be found in the paper linked above. It is a paper I've presented at 2007 SBGf International Congress. Read this paper: it is very interesting and shows the architecture building a seismic to well correlation. This methodology was partially implemented by PUC-TecGraph in Gocad (Paradigm) as a plugin.
Bellow there are some figures about the tools.
Seismic to well correlation from Shift-Drift methodology,
figure from Souza, 2007, 10th SBGF IC
In paper above (green box link) presented at 2003 SBGf International Congress one may find an application of shift-drift methodology. In this case the methodology was used to take real time drilling decisions based on a wildcat LWD profile. The target was to stop drilling at a specific geological position, with some precision (50 m internal to a shale layer and +- 30 m above a interpreted reservoir): the target was reached as previously scheduled.
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