Seismic - Deep Reading Electromagnetics Integration Takes on Deepwater Risk
Authors: Buonora Marco Polo , Zerilli Andrea 
Published: June 2014

Deep water is a complex high-risk environment with no shortcuts to success. Formidable risks must be addressed and mitigated to meet deep water objectives. Cooperative and simultaneous joint inversion of seismic and deep reading electromagnetics (EM) provide a powerful tool for the risk mitigation process. This work gives case examples for the application of seismic-deep reading EM integration to locate the most promising deep water prospects, to reduce uncertainties and minimizing timescale and costs. It underlines the importance of using all available seismic and EM information in the integration of the data, including a rock physics framework to be either numerically derived or empirically calibrated at well locations.

We show that ‘state-of-the-art’ cooperative and simultaneous joint inversion of seismic and EM data are consistently proving to lower exploration risk while maximizing knowledge of the prospects in the deep Brazilian offshore where challenges, logistics, and costs can be formidable.

Today's agenda - deep water oil and gas Exploration is moving into deeper waters, and while rich potential are driving the search ever deeper, the challenges and risks involved are also being amplified dramatically. The oil and gas industry has long realized that information is the greatest tool in mitigating risk. By understanding more about what lies beneath the surface, the risk of drilling a dry hole is reduced. With deep water marine drilling costs topping US $1 million per day, anything that can increase the margin of success is welcomed. A balance must be struck between the cost of gathering more information and the impact this information will have on decisions made further along in the process. The latest developments in high-tech seismic vessels and ‘mega’ channel counts have driven a revolution in seismic data quality and accuracy, as have the post-processing and interpretation tools at the industry's disposal. TTI Reverse Time Migration (RTM), Full Waveform Inversion (FWI) are enabling geoscientists to image large volumes of reservoir quality rocks, even in complex geologies. The availability of low-frequency, long-offset full-azimuth data sets and increased compute power has now allowed FWI to become the preferred method for building detailed velocity models. Still, even with all these advanced techniques, certain exploration challenges remain.

Integration to create value and cut costs Today, workflows are being developed to integrate technologies that reduce the exploration risk in demanding deep water environments. The approach is to develop geologically sound earth models consistent with all of the available data types, then enhance the model by the application of complementary measurements until exploration risk is reduced to acceptable levels. While all of the seismic tools mentioned above tell a large part of the exploration story, many information gaps may be filled in with deep reading EM methods. Seismic techniques may predict the presence of hydrocarbons in a formation, but one of the biggest pre-drill knowledge gaps is formation resistivity. Formation resistivity is one of the most reliable indicators of hydrocarbon saturation levels within a formation structure. Previously this information has only been available through well logs, but now deep reading EM is providing subsurface resistivity information before drilling.