Accelerating exploration

The rapid adoption of seabed logging is setting new standards for the uptake of a gamechanging technology, as Ken Feather, Vice President of Marketing at emgs, explains.

The first commercial application of seabed logging, an innovative electromagnetic (EM) method of locating offshore hydrocarbon reservoirs, was in November 2002. Since then, emgs – the Norwegian company credited with inventing the technique – has conducted more than 200 surveys for almost 40 customers in various parts of the world, an unusually good take-up rate for a brand new exploration concept. Moreover, the technology has been particularly well received by several industry heavyweights, including BP, Chevron, Eni, ONGC, Petrobras, Petronas, Reliance, Shell, Statoil and Woodside.

Boosting drilling success rates

“There is little doubt that seabed logging can significantly raise exploration drilling success rates, historically only around one in four. Our clients, and results from more than 200 surveys, confirm it has genuine game-changing credentials,” says Ken Feather, Vice President of Marketing at emgs. “Not all our customers share their drilling results with us, but seabed logging has correctly predicted the reservoir fluids in more than 90 percent of the 43 cases where we have been able to compare our survey results with their reservoir evaluations.”

Surprisingly, for all the benefits that successful game-changing technologies generate, history shows that they often have a relatively tough time to start with. In fact, the user community tends to reject them, sometimes out of ignorance, sometimes out of fear, but mostly because they generally upset the status quo. They are often, in the best sense of the word, disruptive technologies.

This is where seabed logging does not fit the usual game-changer pattern. As already noted, it has been embraced very positively by the industry. In Feather’s opinion, there are three reasons for this. First, there is a compelling need to improve the industry’s hydrocarbon- finding record, as for the past several years the world has been using oil and gas faster than the industry has been identifying new reserves. Second, seabed logging is seen as the right tool for the job; operators are comfortable with the basic principles behind the technique. The use of EM methods to identify resistive anomalies, and
thus hydrocarbon accumulations, beneath the Earth’s surface is well accepted; borehole logging has been around for 75 years. What emgs has done, however, is to overcome the massive problem of making reliable resistivity measurements remotely – that is, from the seabed. And third, seabed logging is a perfect partner for the industry’s staple exploration technique: seismic surveying.

The compatibility of seabed logging with seismic surveying has probably been the biggest factor in capturing the interest of the exploration companies. That seabed logging does not provide a magic bullet but rather a strong fit with more established techniques has perhaps, unsurprisingly, worked in its favor.

Nobody is going to deny the value that seismic surveying, and recent advances in 3D acquisition and imaging techniques in particular, has brought to the industry. However, seismic surveying has the drawback that although it can identify structures that might be expected to contain hydrocarbons, it is practically blind to any fluids contained in the formation. This explains why roughly three out of four prospects highlighted by traditional means turn out to be dry. No wonder, then, that using seabed logging, which responds to the fluids in the rock, to confirm or discount prospects identified by seismic surveying
has become so popular. It is worth noting that seabed-logging predictions have been confirmed in more than 90 percent of cases where well data have subsequently become available.

Seabed logging is clearly having a significant impact on the oil and gas exploration business; already the technique is being evaluated by the industry for more advanced applications. “We have seen excellent results when using seabed logging for so-called target-oriented surveys. Now, oil companies are routinely using seabed logging in scanning or reconnaissance mode to explore in frontier regions– before they invest in seismic programs,” says Feather.

Scanning for prospects

The rapid increase in demand for oil and gas, which is occurring at the same time as reserves replacement gets more difficult in the established hydrocarbon provinces around the world, is forcing exploration into frontier regions – both deeper water and remote, often inhospitable, unexplored parts of the world. Frontier exploration inevitably means greater risks, increased costs and limited availability of the specialist equipment needed for the task. And, the costs of field development and operation will be far higher than in the established provinces where there is an existing oil and gas production infrastructure. For these reasons, in frontier regions there is a real need to find oil quickly and efficiently – and in large quantities.

Leading oil companies are turning to seabed logging to help them out, as Feather explains: “During several seabed-logging exercises over areas previously seismically surveyed, resistive anomalies were picked up in locations where, significantly, analysis of the seismic data had drawn a blank. This has led some oil companies to re-evaluate their approach to seabed logging and to consider its use as a first-look tool in frontier areas. The idea is to use the technique to rapidly generate leads in areas where large (commercial) hydrocarbon accumulations are most likely to be found. By this means, companies will be able to focus their investment in seismic acquisition, as well as higher resolution seabed logging, and ultimately drilling, on areas that offer the best returns.”

emgs has already adapted and optimized the seabed-logging process for use over sparse grids in what the company is calling scanning mode (Figure 2). When the objective is simply to detect large anomalies, the density of the EM source lines and of the receivers may be reduced, although the company has developed wide-azimuth tech- niques that can identify anomalies that lie between survey lines. And, since preliminary processing of seabed-logging data is also very fast, it is possible to quickly scan considerable areas for large hydrocarbon accumulations, which is very useful in frontier areas such as the Barents Sea, where the weather windows are often very tight.

Naturally, the sparse coverage does not permit the accurate characterization of any finds. However, as a prelude to more targeted seabed-logging and seismic surveys, the scanning process holds enormous potential – and not just for frontier areas. Scanning can equally be applied to mature basins, during the life of an asset, for revealing potential satellite fields or missed opportunities as a final look before assets are abandoned or relinquished.

The scanning data can be evaluated quickly, and detailed infill surveys to investigate the identified resistive anomalies can then be designed and acquired before the vessel leaves the survey area (Figure 3). This fast iterative approach is accelerating prospect delivery, reducing the time to first oil, cutting exploration costs and eliminating extensive exploration in non-hydrocarbon bearing areas.

Over the last 12 months, smarter and more efficient EM source and receiver systems have enabled high-resolution 3D surveys to be conducted using seabed logging. And, looking forward, Feather believes that the technique will also offer the exciting prospect of being able to provide reserves estimates before wells are drilled. The challenge then will be to demonstrate the accuracy of the measurements for accounting and regulatory purposes.

On the evidence so far, and judging by the reactions of many of the leading players in exploration, seabed logging constitutes one of the most important developments in exploration technology that the industry has seen for several decades. And the feeling is that there is more to come.