Saeed A. Al-Yarubi1*, Shadia F. Al-Farsi2, and Nasser T. Al-Touqi2
1Bristol University, UK
2Sultan Qaboos University, Oman
Petroleum Development Oman (PDO) has been acquiring VSP (vertical seismic profile) data for the past 30 years. The different types of VSP data have been used for different objectives. ZOVSPs (zero-offset vertical seismic profile) and OVSPs (offset vertical seismic profile) are considered valuable and are used for time-to-depth calibration, seismic-to-well matching and identification of multiples on surface seismic. The OVSP is normally carried-out in deviated wells or over steeply dipping layers. We will show that the processing of ZOVSP and OVSP is not trivial and how erroneous processing steps or changing assumptions can lead to very different results. This will be demonstrated with a case study of processing ZOVSP with different contractors. WAWVSPs (walk away vertical seismic profile) have typically been used in an attempt to obtain better structural imaging and for time-lapse studies with limited or no successes. In PDO the confidence level in WAWVSPs is often low, resulting from an often-observed poor match of the processed WAVSP data with surface seismic data. This mismatch is observed in the form of: (1) considerable differences in structural dip; (2) events that could be interpreted as faults, which are not present in the surface seismic; and (3) wrong amplitudes differing from surface seismic. In addition to these problems, the bandwidth of the VSP data is not higher than surface seismic, contrary to expectation. These problems will be illustrated with examples of processed WAWVSPs from different fields.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain