Data masters

A Head-to-Head feature with Wavefield Inseis ASA and TGS

Acquiring accurate seismic data is the name of the game for companies looking to fully exploit potential reservoirs. But this task can be made all the more difficult when you throw deepwater surveying into the mix. O&G sought the views of two industry experts, to get a clearer image on this subject.

O&G. What are the critical challenges that the industry faces when it comes to marine seismic data acquisition?
Robert Hobbs. Reserves replacement continues to be a major thrust for TGS’s customers. This is becoming more difficult as the industry moves into more frontier and/or structurally complex geologic environments. As our customers are required to test these more difficult traps, our challenge is to identify and apply the technologies that are fit-for-purpose for the imaging problems that are required in the basins we operate in.

Rick Donoghue. If you are using seismic data as an exploration tool one key factor is to have seismic data of sufficient quality that will allow you to image potential reservoirs that may be in very deep water or in areas where specific rock properties significantly degrade seismic images. So, collecting high quality seismic data tuned to specific exploration environments is a major challenge. When seismic data is used to provide snap-shots, or time lapse images of a producing field over time (known as 4D analysis), then apart from high quality data you also want a highly repeatable acquisition technique so that differences in the seismic images are the effect of changes in the reservoir and not due to ‘camera shake’ to use a photographic analogy. In other words, the challenge is to have the seismic receivers and sources in the same places each time the data is collected.

O&G. How have techniques and technologies evolved so that the industry has accurate and reliable geophysical data at its disposal?
RH. The discipline of geophysics has proven itself to constantly adapt to solve industry’s challenges. There is no other subsurface technology that has advanced more over the past several decades.

Clearly, wide-azimuth (WAZ) and it’s varients, such as rich azimuth (RAZ) acquisition has made the most recent significant impact since the first survey was acquired in the deepwater Gulf of Mexico in 2003. In some structurally complex areas, WAZ has provided a step-change in imaging improvement. Acquisition of these very large surveys is so complex and the resulting data volumes so immense, that the industry is just now interpreting the final processed volumes from some of these surveys.

WAZ acquisition is not just limited to the deepwater towed-streamer environment, but it is also critical to identifying remaining subtle traps around existing production infrastructure where towed-streamer activity is not possible. TGS has been able to leverage the full-wave benefits provided by multi-component ocean bottom cable technology in the search for deep complex traps in these settings. WAZ technology will surely have application in many basins, such as in West Africa where many of the same geologic problems exist.

RD. Many developments have been made to improve acquisition equipment so that high quality pressure and shear waver data are accurately recorded. Pressure waves propagate in both solids and fluids whereas shear waves only propagate in solids. This makes combining both data types very useful in interpreting structures and rock properties but also means that they cannot be recorded in the same way. In order to collect both types of data so called ‘multi-component’ acquisition systems have been developed that incorporate different sensor types.

O&G. Can you explain about some of your more complex projects in the past and what lessons you learned?
RH. It is difficult to cite one specific project, but TGS is finding a continued need and significant value in the integration of various data types in the basins in which we operate. Whether it is electro-magnetic data in the North Sea or near-surface core data and multi-beam information in Southeast Asia, the complex problems that TGS is facing with its clients require a broader toolbox of technologies. TGS has learned from these experiences and fully evaluates all types of geoscientific data that may help a customer resolve these complex situations.

RD. Wavefield Inseis was created in early 2006 so we are relatively new. However, we have a great deal of experience within the management team and we are using this career-long experience to steer the technology advances within the company. Over the last six years we have, as a management team, been very involved in emerging permanent seismic monitoring technologies and techniques. We have, for example, worked closely with permanent seismic system equipment providers to bury some of the first ever permanent seismic sensors into the seafloor in some very challenging marine environments.

During that period we concluded, along with the whole industry, that a completely new technology was needed that would meet the reliability and cost criteria for a system that could be installed into the seafloor to collect seismic data for the entire life of a field. Electrical systems that incorporated standard sensors were just not the best technology to use for this type of seismic application.

O&G. What technologies or developments are around the corner to help exploit clients’ reservoirs?
RH. Seismic data acquisition R&D should be focused on reducing the time it takes to acquire both wide-azimuth acquisition and 4D seismic. One way of accomplishing this is to enable simultaneous shooting with multiple sources. Simultaneous shooting can also increase the source density of the data which provides for a better signal to noise ratio.  Also, the development of wireless seismic sensors are critical for 4D seismic. With increased demand for higher recovery rates in existing oil and gas reservoirs, 4D seismic will be used more in the future to understand reservoir changes by using time-lapsed, elastic inversions of the reservoir properties.

With computer technology advances in the last few years, the industry has used computation-intensive, two-way acoustic wave equation (or reverse time migration) to improve the seismic image. The next step is full elastic wave processing. Full elastic wave inversion or processing (P-wave, S-wave and density) will be used in the future for providing better parameters for reservoir characterisation. Full wave data (3-component) acquisition will provide the data needed for elastic wave processing.

Azimuthal anisotropy, which is key for estimating the density and direction of subsurface fracturing, can be used now that techniques such as WAZ are providing a greater range of azimuthal coverage.

RD. In fact we have just turned a major corner and the new technology for the future of seismic in now available. The Optowave permanent seismic system from Wavefield Inseis is comprised of four component (4C) seismic stations that contain optical sensors. This allows shear wave data to also be collected which greatly enhances reservoir imaging leading to improved reservoir monitoring and management. The system also uses fibre optic lead-in cables and a laser interrogation instrumentation system placed at the surface.

The subsea components of the system are completely passive in that they have no electronic components whatsoever and so no power is required. The passive nature of fibre-optic sensors embedded into 4C receiver stations is an advantage over traditional electrical systems since the in-sea sensor equipment is not prone to electrical noise, leakage or short-circuit. The low power loss and large bandwidth of optical fibres enable extremely high data transmission rates over long lead-in cables and allows the transmission of huge amounts of information over tens of kilometres.

An additional and very important factor is that the fibre-optic receiver cables are less expensive to manufacture than the traditional electrical receiver systems. All of these advantages make the fibre-optic sensor technology perfectly suited to be utilised in ocean bottom receiver cables in connection with life-of-field seismic projects. In October this year Wavefield Inseis were awarded a contract to install the first of these systems over the Ekofisk field in the North Sea. A new era has begun.

About the contributors:

Rick Donoghue, VP Marketing and Sales for Wavefield Inseis ASA, has 30 years of experience within the geophysical services industry with Schlumberger, WesternGeco, Multiwave Geophysical and CGGVeritas. During his career he has had a variety of roles in offshore management, data processing, land acquisition, marine operations, international sales and marketing. He holds a BSc in Physical Geology from Exeter University in the UK.

Robert Hobbs joined TGS in 2008 as Chief Operating Officer. He has more than 20 years of experience in the oil and gas industry, including previous appointments at Exxon, Union Texas Petroleum, Veritas DGC and Marathon. He has served in a wide range of technical and leadership roles from Geophysicist, to President and Managing Director. He holds a MSc degree in Geology from the University of Southern California.