Vertical seismic pitfalls: problems in archiving VSP data

Companies need to make sure that their treasured VSP data is archived and in good order, warns Eleanor Jack, senior geophysicist of Landmark's Information Management Practice. She provides some horror stories of what all too frequently can go wrong to prove her point. VSPs (Vertical Seismic Profiles) are the bridge between wells and seismic, the point where time and distance meet, where the generalities of the surface seismic data are anchored to the certainty of the well. As such, VSP data should be the securest items in the archive, the ones in which we have the most confidence. And yet, when we come to archiving VSP data, we find ourselves in a no-man’s land of conflicting formats, procedures, and practices, where hardly anything is standardized and everything is at risk. How can this be? Summary of problems The problem is partly that no-one really knows where to put VSP data, which do not fit comfortably into a well database, because they are mainly seismic, and do not fit into a seismic database, because they belong to a well. Moreover, there is, or rather, should be, a variety of different data types such as reports and calibrated logs in addition to the seismic, all of which have different archiving and indexing requirements. VSP seismic data too, have their own special problems, involving as they generally do, X, Y, and Z components. Multicomponent VSP data arrived on the scene well before anyone had devised a format to cope with them and the data therefore had to be shoe-horned into the SEGY format in a variety of ingenious ways. (SEG-Y Rev 1 finally addressed this problem in 2002, by which time a 20-year or so backlog of multi-component original SEG-Y had accrued). Processing of these data has never really been standardized, and this has resulted in a great diversity of processed data. Data were processed with very little concern over who else, other than the perpetrator, would need to read them and this led to some truly bizarre interpretations of what the SEGY format actually meant. As if this were not enough, there is a fundamental difference of approach between the well and seismic camps on the matter of encapsulation. Use of TIF (Tape Image Format) encapsulation is standard for well logs but not, unfortunately, for seismic. An archive involving both logs and seismic may well therefore be a mixture of encapsulated and unencapsulated data, but if archivists attempt a unified approach and encapsulate their seismic data, this will render them unreadable to most applications. This subject will be revisited in detail in one of the examples.