Throughout the history of reflection seismic data acquisition there has been a continuous increase in the acquired field trace density as new acquisition and processing technologies have emerged. As a consequence, the E&P industry has seen consistent improvements in final seismic data quality. In this month’s RECORDER Focus section, we present three papers that show how current emergent technology innovations are changing the way that seismic data are acquired in Canada.
The relationship between trace density and seismic data quality has long been recognized anecdotally, but until recently it had not been thoroughly investigated.
In a series of papers published over the last two years, BP quantified the impact on data quality from the decimation of the 64 km2 ultra-high density, full azimuth Risha 3D survey. This survey was acquired onshore Jordan with a trace density of 41 million traces / km2 or 41 traces / m2. The data were decimated to simulate alternative acquisition geometries, generating data sets with densities as low as 0.16 traces / m2. After processing, conventional and azimuthal attributes were extracted and compared with the same attributes extracted from the densest benchmark volume. These comparisons clearly demonstrate that attribute quality declines as trace density is reduced, with rock property attributes showing the greatest sensitivity to input trace density (Ourabah, et al., 2015).
By comparison, a typical Western Canada 3D delivers trace densities between 0.05 and 0.1 traces / m2, which is lower than the lowest trace density in the BP experiment. A Canadian example of the improvement in 3D seismic data quality that can be achieved by an increasing trace density was provided by Thacker et al. (2014). They observed similar improvements in frequency content and signal-to-noise ratio to those seen in BP’s Risha experiment. Based on these two results, we believe that the quality of Canadian 3D seismic data can be increased considerably by acquiring significantly higher trace densities than those that have been acquired to date. We expect that this increase in seismic quality will feed through to improved business decisions, to added business value, and to improved E&P company performances.
Several enabling technologies and techniques have emerged over the last few years that we believe have yet to deliver their full potential in Canada. Primarily these include nodal recording systems that employ a GPS signal to synchronise timing, and the use of simultaneous, distributed, seismic energy sources that also use a GPS signal for synchronization.
Nodal receivers use GPS time signals in order to maintain their temporal sampling integrity. As Châtenay and Thacker (Deriving High Quality Horizontal Positioning of Seismic Receivers Directly from GPS Receivers Embedded in Wireless Seismic Receiver Nodes) show in this issue, this GPS information can also be exploited to deliver reliable positioning information. Their inherent positioning flexibility and ability to deliver reliable positioning data, allows for efficient deployment of much denser receivers without compromising far offset data.
New denser designs are now emerging that enable geoscientists and seismic crews to break out from the “receiver line” and “recording patch” paradigms, and to deploy the nodes in a fully stake-less operation following lines of least resistance. This has important implications for designs and methods, and will dramatically reduce environmental impact while creating data volumes with much higher trace densities.
In the second paper (Technology Collaboration is the Key Element in Frontier Seismic Exploration), Jason Criss offers a concise summary of the impact of these emerging technologies in challenging areas, and describes how using a reduced size vibrator is highly complementary to the capabilities that are unlocked by distributed nodal receivers in these areas.
In the international arena the use of simultaneous distributed sources, both onshore and offshore, has proven to be a very effective tool to dramatically increase trace density and to deliver improved seismic data quality. Single vibrator, single sweep acquisition has been shown to be effective in Western Canada (Thacker et al., 2014) and Ann O’Byrne documents another successful example of this approach in this issue (Field Testing Justifying Significant Changes in 3D Design Parameters to Improve Seismic Data and Decrease Costs). The use of simultaneous source techniques, such as slip-sweep, has recently been accepted by several operators in Canada; and these techniques have the potential to deliver dramatic increases in recorded trace density and significant increases in seismic crew efficiency.
Explor recently completed a 3D survey in NW Alberta using a nodal recording system and a single vibrator, single sweep, slip-sweep source to deliver trace densities of up to 2.4 traces per m2. We believe that in future programs across large parts of Western Canada, it will be perfectly feasible to increase this trace density many times over simply by more fully utilizing the available nodal receiver inventory, and by extending the use of available simultaneous source technologies.
In the early 1980’s one of the authors remembers a Chief Geologist from a large E&P company trying to disband the company’s in-house seismic acquisition team. Luckily he was unsuccessful, and members of that team went on to invent, or to inspire, a number of acquisition technology innovations that our industry continues to benefit from today. We believe that seismic acquisition technology continues to be a vibrant and exciting arena to work in, and we look forward to embracing and exploiting new technologies as they emerge so that we can continue to add value to the Canadian E&P industry.
About the Author(s)
Ourabah, et al., 2015, Impact of acquisition geometry on AVO/ AVOA attributes quality – a decimation study onshore Jordan: 77th Annual International Conference and Exhibition, EAGE.
Thacker, et al., 2014, An evaluation of single vibrator, single sweep 3D seismic acquisition in the Western Canada Sedimentary Basin: CSEG RECORDER, v.35(5)