First Break - Volume 28, Issue 5, 2010

Lucy MacGregor1 and Richard Cooper suggest that for marine controlled source electromagnetic survey methods to achieve more general adoption in the E&P industry, the applications need to be refocused with more emphasis on prospect appraisal and reservoir monitoring rather than exploration.

A. Lovatini, K. Myers, P. Watterson and T. Campbell1 describe how controlled source electromagnetic (CSEM) data were acquired and integrated into a study of the Potiguar basin offshore Brazil to improve understanding of the petroleum geology of the deepwater area.

Stein Fanavoll, Jonny Hesthammer, Jens Danielsen and Aris Stefatos provide the most detailed analysis to date on the effectiveness of controlled source electromagnetics as a tool for the detection of commercial volumes of hydrocarbons.

Chris Anderson and Johan Mattsson introduce a new surveying method being developed by Petroleum Geo-Services to allow marine electromagnetic (EM) data to be acquired in the same way as seismic data. Successful implementation could lead to a common acquisition platform for both seismic and EM surveys.

David Myer, Steven Constable and Kerry Key of the Scripps Institution of Oceanography describe the first fully academic marine CSEM and MT survey of a hydrocarbon reservoir.

Adam Wooldridge reviews improvements in airborne gravity systems over the last 10 years and, on the evidence of 200,000 line km, demonstrates the overall capability of the GT-1A system under standard survey conditions.

Antonio Menghini, Giuseppe Pagano, Stefano Floris, Emanuele Bernini and Matteo Pelorosso report on the successful use of a time domain electromagnetic method in a geophysical survey for the detection of hydrothermal water near Viterbo, Italy.

Near surface complexity can be particularly challenging in the case of shallow targets, such as the Kuwait Lower Fars heavy oil field. Claudio Strobbia, Adel El Emam, Jarrah Al-Genai and Jürgen Roth discuss the results of a joint study with a presentation of new approaches for point-receiver data acquisition and processing.

We study surface deformation monitoring over a hydrocarbon reservoir in the Middle East with permanent scatterer interferometric synthetic aperture radar (PSInSAR). By combining data from two different observation angles, it is possible to disentangle horizontal and vertical deformation of the Earth’s surface. We benchmark the PSInSAR data against an existing GPS network and find good agreement in both vertical and horizontal displacements. In order to relate the surface data to the reservoir, we invert the surface deformations using an analytical geomechanical model and obtain reservoir strain. Assuming linear poroelasticity, we relate the strain to pressure depletion. The areal extent of the reservoir strain is in good agreement with predictions from reservoir simulation. By considering velocity gradient maps, we find intriguing relationships between major faults in the reservoir and the surface data. We conclude that surface deformation monitoring and geomechanical inversion can provide valuable information on dynamic reservoir behaviour.

A case study from the Elgin-Franklin fields is used to illustrate the influence of seabed low velocity anomalies on imaging deep targets below 5000 m depth. In the uppermost 400 m of sediment, glacial channels are present and generate locally low velocity anomalies resulting in pull-up/push-down effects observed on seismic reflection data. The original 3D prestack depth migration did not take into account these shallow velocity anomalies, but used a smooth interval velocity in the uppermost layer of sediment. In the southern area, the results were locally better than with prestack time migration, but in the northern area they were worse, or at best comparable. A new velocity model with a channel layer was built using well velocities for the initial model. Tomographic and migration iterations were used to refine all velocities, including the channel velocities, and for introducing anisotropy. Imaging of the pre-Cretaceous section was clearly an improvement over prestack time migration. For correct imaging, local shallow velocity variations must be identified and taken into account in the velocity model. Even though the overburden appears to be rather flat, prestack depth migration imaging performs better than prestack time migration overall.