--> ABSTRACT: Log of Formation Parameters While Drilling, by S. Serbutoviez, C. Naville, J. B. Fay, F. Verdier, G. Billet, and F. Batini; #90906(2001)

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S. Serbutoviez1, C. Naville1, J. B. Fay1, F. Verdier2, G. Billet2, and F. Batini3

1Institut Français du Pétrole, Rueil Malmaison, FRANCE
2Gaz De France, La Plaine St Denis, FRANCE
3ERGA S.p.A., Pisa, Italie

ABSTRACT: Log of Formation Parameters While Drilling

The var iations of formation stiffness are tentatively quantified using mainly the axial drill bit acceleration compensated with the appropriate drilling parameters in order to produce a continuous log while drilling. The acceleration can be measured on top of the drill string or down hole depending on the well deviation. The root mean square acceleration is calculated over every drilling time segment of 30 seconds, then it is displayed versus depth. Simple compensations are applied with the drilling rotation (RPM) and the rate of penetration (ROP) recorded on the drill site. As the obtained log is closely related to the P-wave acoustic impedance calculated from the standard wire line sonic and density logs, this new log has been called "Pseudo acoustic Impedance Log" (PI-log) Comparisons of the pseudo impedance log with the acoustic impedance computed from the sonic and density logs have been produced from several field examples. Good correlation has been obtained in homogenous formations with strong impedance variations. Differences are observed in micro fractured and fractured formations. In one example with a Polycristalline Diamond Compact (PDC) bit, the axial and torsion acceleration logs have been produced and only the axial acceleration variations seem to be related to the lithology. If check shocks times are available while drilling, the pseudo log can be converted into seismic times to improve the seismic well tie. As the pseudo log can be obtained while drilling, it could be a good indicator of the lithological changes at the bit in real time and could help in the following applications:
· positioning of the drill bit on the seismic section,
· early detection of over pressured formation,
· definition of coring/casing points...
· formation evaluation when used with other logs

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado