A seismic shift in thinking

Recent advances in data acquisition and processing techniques makes Vertical Seismic Profiling (VSP) is a crucial tool in maximising a reservoir’s potential. O&G hears more from expert Saleh Barakat.

“As companies look to exploit fields that are more complex and difficult to drain, tools such as VSP will be necessary for economically viable recovery”
-Saleh Barakat

How are borehole seismic applications helping to achieve maximum results from oil company’s wells?
Saleh Barakat. Borehole seismic, in particular Vertical Seismic Profiling (VSP), unites the time and depth domains, the geology and geophysics, for a more reliable picture of the reservoir. VSPs have been used for several decades, but recent advances in data acquisition capabilities and processing techniques have made them indispensable for optimum reservoir management. Companies like VSFusion continually fund research into improved processing techniques, to deliver the maximum amount of information from each VSP dataset, in as short a time as possible. The results give improved returns on information investments from well logs, surface seismic and reservoir geophysics, and greater potential for enhanced field development – getting more oil hydrocarbons out of the reservoir with less financial risk for all stakeholders.

Are there are any particular borehole seismic challenges that the MENA region faces?
SB. The quality of seismic data from the region is generally very good, but is characterised in particular by high amplitude multiples. Also, there are often vertical fractures in the carbonate reservoirs like the Khuff and the Arab-D. In VSFusion, we look on these as opportunities rather than challenges. For example, we have developed an innovative technique to migrate the first-order multiples in VSP data using our patented 3C Vector Kirchhoff migration, which gives reflectivity from TD to surface, and over a much wider lateral extent than with conventional VSP imaging. The principal fracture directions and the resulting anisotropy can be measured using VSP, and the results fed back into the surface seismic processing route, to enhance the surface seismic image.

Could you explain about the benefits of VSP for well characterisation, even in the most difficult of geological environments?
SB. One major advantage of VSP data over conventional surface seismic data is the bandwidth. Because the VSP travel paths are half what they are in surface seismic data, we typically see a 20Hz or 30Hz improvement in bandwidth, and the corresponding improvement in vertical resolution. Faults that are invisible to surface seismic data suddenly come to life with VSP. Users see smaller features, both in the vertical scale and laterally away from the well and can confirm borderline seismic interpretations. In addition, VSFusion has helped to develop specific techniques, such as Virtual Source, to allow accurate imaging in complex areas, for example beneath salt domes, areas that are notoriously difficult to image using conventional seismic methods.

What are your future predictions for borehole seismic applications and VSP and how will technology play its part?
SB. The advent of large, reliable, wireline-deployed geophone arrays, like the 100-level tool offered by Baker Hughes’ SeisXplorer service, give the opportunity to record and process large 3D VSPs, with data volumes that are more than 10 times larger than those of only a couple of years ago. With these large arrays, there is enough data recorded to allow companies like VSFusion to process not only high-resolution P-wave and S-wave cubes, but to measure azimuthal anisotropy and AVO, and to make detailed studies of the fracture networks at the well, all from the same dataset. 
 
Even now, VSP processing can now be done almost in real-time, and can be used for geosteering and hazard avoidance during drilling. This is achieved by measuring the depth and two-way time, to place the drill bit precisely in the surface seismic section; we can update the velocity model in real-time, to allow re-migration during drilling; and VSP reflectivity can be inverted to acoustic impedance, to predict overpressures ahead of the drill bit. These real-time applications are big money-savers, and are moving borehole seismic interest and information away from the desk of the geophysicist to the desks of reservoir engineers, geologists and drillers – those concerned with the bigger picture of field development. As companies look to exploit fields that are more complex, more fragmented and difficult to drain, tools such as VSP will be increasingly necessary for economically viable hydrocarbon recovery.

As VSFusion Middle East Region Manager at Baker Hughes, Saleh Barakat’s major expertise includes surface and borehole seismic data interpretation, 3D & 2D VSP data. He has over 21 years of working experience in geophysics, including eight years at AFPC (Shell International & SPC Joint Venture. Barakat joined Baker Hughes in 1997 as a senior geophysicist.