C. Naville1, S. Serbutoviez1, J. Bruneau1, H. Japiot2, R. Daures2, and J. Y. Gaborit2
1Institut Français du Pétrole, Rueil Malmaison, FRANCE
2Compagnie Générale de Géophysique, Massy, FRANCE
ABSTRACT: SEISDIP : The “VSP dipmeter” from Oriented 3 Components
VSP surveys are commercially recorded with a single zero-offset source position and with a downhole tool including 3 orthogonal seismic sensors. For VSP acquisition in vertical wells, a hardware orientation accessory needs to be combined with the VSP tool.
An “isotropic” processing of the oriented 3 Components (3C) VSP data is necessary, meaning that all the processing operations are identically applied on the 3 components at any seismic time, ensuring the following benefits:
The illumination of seismic reflectors is achieved in 3 Dimensions, with information about their dip and azimuth (SeisdipTM method). 3C VSP yields the structural dip of seismic interfaces from the borehole up to distances of several hundred metres away from the well, even if the reflectors do not intersect the well, or are located below the well. A 3C VSP can be recorded in any well, cased or open hole. In contrast, electrical dip - meter log measurements relates to sedimentary dips within centimetres away from the well bore, and can be recorded in open hole only.
Reliable identification and improved discrimination of the upgoing VSP events: P or S reflected, diffracted and refracted arrivals. Only three component processing allows to disentangle a complex seismic wavefield containing mixed P and S wave mode arrivals coming from varied dipping reflectors, potentially curved, and from diffracting fault corners.
In case of interfering reflected/diffracted e vents generated by lateral dip variations or tilted faulted blocks, 3C processing allows to fully understand the VSP response, while the conventional single component processing can mislead the interpreter.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado