MEOS lookahead: Seismic

Ahead of the event, Bob Heath of Seismic Source & iSeis about the latest developments in seismic. Seismic Source & iSeis will be attending MEOS.

New vibroseis control products enhance acquisition techniques

In the last few years, the land exploration industry has witnessed the introduction of a number of novel, high efficiency vibroseis techniques, including BP’s ISS, DSSS and variations thereof, as well as ZenSeis from ConocoPhilips.

Other oil companies are also devising their own new methods, a few of which seem broadly based on the fundamental innovations outlined by these and other oil companies such as Shell and ExxonMobil. These techniques and their variants have the potential to bring about a whole new vibroseis era and new ideas are now being introduced into impulsive shooting too. This is all (a small) part of what is now increasingly being called “future-seismic”. Whereas expectations are high, hardware to make such techniques as productive as they ought to be has only very recently become available.

The problem is that such new acquisition methods can pose unexpected problems not just for the recording instrumentation itself but also for any source control equipment which was developed before anyone envisaged techniques so flexible. The oldest systems almost certainly restrict the ways in which these some of these methods can be exploited, and these limitations may not be apparent till the operator goes to the field, or until end-users try to start to ramp-up productivity rates.

Seismic Source Co., of Ponca City, Oklahoma, is the world’s largest independent centre for vibroseis research and development. Its unrivalled facilities permit new techniques to be field-tested and hardware/software to be developed to work with a wider range of acquisition systems and vibroseis controllers than any other company’s in the world, and now SSC’s new SourceLink solution tackles many of these new problems. With a flexibility which has not before been possible it provides simultaneous control and QC of all sources on the project, including multiple dynamite, weight drop, airgun and/or vibrator groups. This also makes it ideal for use with continuous recording systems such as iSeis’s Sigma cablefree recorder, as well as OYO’s GSR, Fairfield Z-land and Sercel’s Unite system.

SourceLink software offers a graphical map interface for each group, selecting the nearest flag while automatically finding the CoG of each group and taking the shots. The real time status of each group is provided, showing distance to flag, sweep/ready status, the EP number within the VP and error conditions and so on. It efficiently supports all simultaneous vibroseis methods such as HFVS, Slipsweep and its derivations, ISS, Zenseis, and combinations of these.

Where these techniques result in a large number of independent sources on the spread communication with each source is vital. This is provided via SSC’s TDMA server system which does away withe need for expensive digital radios where communication may be limited to a relatively low number of groups. The TDMA hardware can make use of standard analog crew radios and any permitted RF power. The result is the ability in real time to display source performance of, for example, the last 100 sweeps while focussing on any problem areas. PSS data is displayed graphically and out-of-spec or missing shots can be identified. For dynamite operations, different uphole times in different colours show variance graphically. Google Earth images can even be easily added to any prospect.

The TDMA system includes hardware and comprehensive software for almost every conceivable set-up. The “TDMA Server” is essentially a complete recording system. It includes all SPS driven software and everything necessary to interface to the geophysical recording instrument to handle all the latest vibroseis techniques. It also incorporates Ethernet communications, GPS timing, GPS positioning (can be almost any GPS type), and source signature recording. The maximum number of independent sources that can be handled is a staggering 255, a massive leap over anything previously.

SourceLink operates not only with SSC TDMA system but also with a variety of source control equipment, including SSC’s own new Force Three encoder/decoder, as well as SSC’s long-established Universal Encoder, Force Two vib’ electronics and BoomBox blaster unit, and weight drop control systems. It can also be used with Pelton VibPro and ShotPro hardware.

SourceLink offers immediate benefits for all vibroseis and impulsive operations anywhere in the world, improving production rates in all shooting modes, savings hours per days in any type of operation.

Passive acquisition and permanent monitoring breakthrough

Passive seismic acquisition and permanent monitoring are often considered less demanding of equipment than traditional exploration with controlled surface sources. Whereas there may have been some truth to this a few years ago, it is the latest requirements for non-active recording which are now pushing hardware to the limits. And it is the Sigma cableless system from iSeis is which is setting records in the field due to a variety of unique features which make it ideal for these difficult environments.

At the EAGE’s Passive Workshop in Athens, a number of papers were presented discussing better and new ways to gather information about the reservoir without use of active sources. What the realisation of some of these ideas may have lacked is equipment capable of taking on the recording task, perhaps due to cost, flexibility or even simple specifications. A paper by iSeis’ Bob Heath showed how Sigma cableless recorder can change all that. (This paper was followed up with an article expanding on the subject in July 2011’s First Break).

Passive and permanent monitoring systems are generally listening for much smaller signals than are common in active acquisition, and may also be interested in lower frequencies than many standard 24 bit recorders are designed to measure. To cope with this, Sigma uses a 32 bit convertor providing a far larger dynamic range than is typically found in equipment primarily designed for active acquisition and optionally can be supplied to acquire signals below 1 Hz.

Non-active recording may also need to take place over very large areas, perhaps hundreds of square miles. And while all equipment may need to be monitored continuously, cabled or shootblind cableless systems are clearly inappropriate. However, these problems are solved by Sigma’s unique in-built mesh radio network, which also allows essential remote control of hardware. The MRN permits an operator in a central location to safely monitor huge live remote spreads of equipment, and is even able to import images from Google Earth, ensuring no data or hardware is lost.

Permanent installations also usually assume that recording takes place to all intents and purposes indefinitely, twenty four hour per day. Essentially, the flow of data can be considered relentless and losing just a single frame may miss an important event. Therefore, in order to call itself a “modern recording system” the important criteria are that it can handle this massive amount of incessant data, offer either real-time recording or a capability which allows very rapid data retrieval without disturbing recording, and ideally – both, as is possible with Sigma.

When data is not required in real-time, high sample rates and longer recording durations nowadays encountered in the passive/permanent environment can mean that (a) very large memory capacities are necessary, and (b) far more flexibility is required in data harvesting. Sigma ground units not only have huge memory capacities but also multiple methods of harvesting, including wifi for pass-by downloading, and even USB copying, none of which require recording to halt or ground units to be collected up. When it is necessary to return data in real time, Sigma is the only system which is field-proven and shown capable of doing the job over very large areas and the most awkward geometries.

However, there are some passive recording situations, such as fracing, where a cabled architecture may not be so disadvantageous and for this reason, Sigma offers the options to hardwire its ground units together. Sigma is the only cableless system able to offer this.

Finally, as the distinctions between what passive, permanent and active recording requirements become ever more blurred, it is increasingly important for one recording system to be able to take on all types of operation. Only such universal equipment can solve so many of the acquisition problems being encountered in this industry.