Offshore seismic solutions

Nina Rach

June 20, 2014

Five exemplary geophysicists took part in a panel discussing “Emerging Offshore Geosciences Technologies” at the 45th Offshore Technology Conference in Houston, all of whom have dedicated years of service to the Society of Exploration Geophysicists (SEG), one of OTC’s sponsoring professional organizations. Nina Rach reports.

Marine streamers

David James Monk, Director of Geophysics at Apache Corp., talked about advances in marine streamer technology and novel acquisition geometries. Broadband seismic allows deeper imaging through the inclu- sion of lower-frequency data, and “you really want the lowest frequencies you can get,” he said. Acquisition techniques that reduce seismic ghosting (reflections from the sea surface), such as towing streamers at different depths, and using sampling pairs, such as pressure and velocity fields, or pressure and acceleration, ultimately improve data quality.

Simultaneous-source acquisition may become more common offshore, resulting in more data acquired faster.

Monk believes bandwidth will increase to one million channels within a decade. Technology to position streamers has advanced, he said, and may result in shooting “strange geometries that we can’t even begin to imagine today.”

Monk earned a PhD in physics at University of Nottingham, and worked in R&D on seismic acquisition and processing at Geophysical Service Inc. (GSI) and Halliburton Geophysical Services Inc. (HGS) for 18 years, then served as President at Energy Innovation Services before joining Apache in 2000. Monk served SEG as Chairman (2008-2011), and as President (2012-2013).

Permanent reservoir monitoring

Rocco “Rocky” Detomo discussed using permanent reservoir monitoring systems (PRM) offshore, citng BP’s Life of Field Seismic (LoFS) program at the Valhall field off Norway. BP Norge covered a >45sq km area with permanent ocean-bottom cables and

ran 15 surveys. Success at Valhall led BP to install PRM on the Clair field off UK, and at the Azeri-Chirag-Gunashli complex in the Caspian Sea. LoFS systems make sense, Detomo said, if companies plan repeated surveys over a field.

He also mentioned several types of seabed geodesic systems to measure subsidence and lateral movements, and suggested that systems could be integrated to provide different types of measurements.

Detomo discussed permanent wellbore sensors, which incorporate distributed acoustic sensing fiber-optic systems that he expects to be deployed more widely. The future should bring improvements in fiber-optics, with more sensors, channels, and receivers. Other promising technologies include autonomous recording, seafloor power solutions, and optical data transmission.

Detomo earned a PhD in experimental nuclear physics at the Ohio State University, after which he worked for Shell and received Shell’s 1991 President’s Award. He recently formed Omoted Geophysical Consulting. Detomo has served SEG in many capacities, as technical program chair for the 2006 Annual Meeting, Chair of the Travel Grants Committee, Trustee Associate of the SEG Foundation, and travelled as the SEG 2012 Honorary Lecturer in the Middle East & Africa, discussing 4D time-lapse reservoir monitoring. Detomo is Vice-Chair of the SEG subcommittee for the OTC 2015 technical program.

Seabed hardware

Shuki Ronen, Seabed Geosolutions BV, questioned whether PRM is the future of reservoir geophysics.

Non-permanent technology, including streamers and ocean-bottom nodes, can also provide proper reservoir monitoring, especially with faster shooting and better broadband sources. Sometimes it is a good idea to put receivers on the seabed; sometimes it is not, Ronen has said. “I want to encourage people to know where and when and how to put seismic receivers on the bottom of the ocean.”

4D reservoir monitoring often requires seismic surveil- lance in congested offshore areas, where obstacles deter full streamer spreads. Ronen points out that seabed receivers present fewer safety challenges than surface-towed streamers. Permanent or accurately repositioned receivers also have improved repeatability for reservoir production monitoring. Ronen anticipates more remotely operated vehicle-enabled installations and longer battery life.

In addition to improved P-wave imaging, multicomponent seabed receivers record shear waves, which can help distinguish between effects of fluid change and pore-pressure change.

Ronen earned a PhD in geophysics at Stanford University and works in academia and the oil industry. He was a visit- ing professor at Colorado School of Mines, and has been a consulting faculty member at Stanford since 2008. He worked at Saxpy Computer, Schlumberger and Veritas DGC in various positions for 18 years, before consulting for Chevron, joining Seabird, and then serving as Vice President for Ocean Bottom Technology at CGGVeritas. Ronen is now Chief Geophysicist at Seabed Geosolutions (JV between Fugro and CGG). He received an SEG Special Commendation in 2002, recognized as one of the four principal developers of Seismic Un*x, and in 2012 served as SEG North America Honorary Lecturer, discussing “Ocean-bottom acquisition and processing: past, present, and future.”

Microseimic monitoring

AAPG member Peter M. Duncan, president and CEO of Houston-based MicroSeismic, discussed the achievements and promise of microseismic technology.

“Microseismic monitoring is to [hydrau- lic] fracturing as logging is to drilling,” Duncan said. It helps show which parts of a reservoir are draining, and points to the best areas to put future wells. “Optimal well spacing,” he said, “is what operators need to know.”

He said passive measurement was useful for monitoring production as well as induced seismicity resulting from injection, and would be part of the smart oil field of the future.

Passive monitoring also provides transparency into oilfield operations. “The oil and gas industry recognizes the need to remain good stewards of our environment and are proactive in developing technologies and practices that ensure responsible oversight,” said Duncan.

Duncan earned a PhD in geophysics from the University of Toronto and has spent his career at Shell Canada, Digicon Geophysical, ExploiTech Inc, which became a subsidiary of Landmark Graphics, and 3DX Technologies Inc., before found- ing MicroSeismic. Duncan served as SEG President in 2003- 2004, and as Fall 2008 SEG/AAPG Distinguished Lecturer.

4D/4C off Brazil

Paulo Johann, corporate reservoir geo- physics manager at Petrobras Brazil, discussed how the company is using PRM technologies.

In 2005, Petrobras ran an ultra-deepwater, 4-C seismic acquisition program in the Campos and Santos basins. It began with a feasibility study that indicated the potential value of multicomponent technology. Petrobras used illumination analysis to design the survey and had fully processed data within seven months.

In late 2012, Petrobras installed the first deepwater PRM system at the Jubarte field, in Campos basin. The Jubarte area is crowded with obstacles, with 60 fields, 567 wells, and 51 platforms, and would appear to be a perfect candidate for PRM because of the complex infrastructure.

A PGS Optoseis system was installed in 1200m-1350m water depth in the south part of the field. The sensor array included 35.6km of seismic cables arranged in two subsea array loops covering 9sq km, containing 712 4D-4C receiver stations at 50m intervals. The objective was to validate the ability of fiber optic sensing technology to detect reservoir impedance changes.

Traditional offshore seismic surveys produce less than 500,000 seismic traces/sq km. High-density surveys provide around 1 million traces/sq km. But the Jubarte PRM acquisition geometry generates more than 3.8 million traces/sq km of multi- azimuth and multicomponent data.

Johann joined Petrobras in 1981. He has been involved with internal Petrobras training programs for new geophysicists and geologists and was PRAVAP (Research IOR Program) coordinator in geophysical technology. Johann earned a D.E.A. and PhD in reservoir geophysics from Paris VI University, as well as MBAs from FGV and COPPEAD. Johann was the first SEG Latin America Honorary Lecturer (2008) and was vice-president of the Brazilian Geophysical Society, SBGf (2003-2005) and SEG (2008-2009).