Introducing Electromagnetic Surveying in MexicoWed, 01/25/2012 - 17:16
From as early as the 1930s, data was taken from drilled wells using a technique developed by oilfield services company Schlumberger Limited known as borehole resistivity logging. Whilst this technology developed over time, the premise was a simple one: a borehole resistivity log would measure the dierence in resistivity between brine-filled sand, which has low electrical resistivity, and oil-filled sand, which has much higher electrical resistivity. However, as Dave Ridyard, President of EMGS Americas points out, “The biggest problem with a borehole resistivity log is that in order to obtain the data, you need a borehole. In order to obtain that information you have to spend US$100 million drilling a well. We thought it might be nice to have that information before spending that money, rather than afterwards. We try to give our clients an idea of what the chances of drilling success are from the seabed rather than once the well has been drilled.”
Ridyard explains that the inventors of the technology, Svein Ellingsrud and Terje Eidesmo, had something of a ‘eureka’ moment in the late 1990s whilst working for Norway’s national oil company Statoil regarding application of electromagnetic (EM) technology to map hydrocarbon reserves from the seabed. “After carrying out theoretical and modelling tests in test tanks in Norway, Ellingsrud and Eidesmo secured a commitment from Statoil to further develop their idea through a field trial. Borrowing equipment from the University of Southampton and Scripps Institution of Oceanography, the team tried a proof of concept survey in Angola, which was a success.” Rather than internalizing the technology, Statoil decided to use the invention as the basis for new company, and transferred all the intellectual property and patents into EMGS.
In less than a decade, EMGS has developed its controlled source electromagnetic (CSEM) technology through more than 500 surveys. In 2008, the company acquired its first purpose-built vessel. “In comparison to the development of seismic technology, EMGS took about 90 years of development and compressed it into ten years,” Ridyard says. “We naturally learned a lot from the seismic industry. We already knew, for example, that 3D was better than 2D, and wide-azimuth 3D was better than narrow-azimuth 3D. We had also learnt that if you are going to acquire cost-eective 3D data, you can’t do it from vessels of opportunity; you have to use vessels which are designed for that purpose. So we hit fastforward and pushed 70 or 80 years of development into a ten-year time period.”
Today, many of EMGS’s clients use CSEM technology to complement their seismic data and increase the percentage of successful wells drilled. Ridyard explains that many times, a company will conduct its first CSEM survey in an area where they have an existing well in addition to a prospective hydrocarbon deposit. In this way, they can benchmark the results produced at the existing well in order to gauge the ecacy of the technique. “90 percent of our customers will do 3D seismic first,” says Ridyard. “The idea for many companies is to spend a little extra to improve the chances of drilling a successful well. However, we are starting to see some customers getting creative when they conduct their CSEM surveys. It is still a radical concept, but some of our customers are starting to experiment with only conducting a dense 2D seismic run and a CSEM survey before drilling.”
In its standard form, CSEM is not only rapidly gaining customers, but also developing its ability to improve the chance of drilling success. “When an E&P company has gone through its seismic data on a prospect, the chance of drilling success stands at roughly between 25-30%. EM data is very good at disproving the existence of wells – our success rate in negative EM is 99%,” Ridyard says “When it comes to positive EM, it seems that so far our customers are seeing between 50% and 70% drilling success once our data is laid alongside seismic data.”
However, the rapid development of CSEM technology does not come without a price. “As a result of EMGS’s rapid development of this technology, the consulting companies and the interpretation software companies are a little behind the curve. They have wonderful tools for interpreting seismic data, but they don’t have the equivalent tools yet for interpreting EM data. It’s therefore not as easy for oil companies to consume our data as it is for them to consume seismic data. I think the next big barrier for EMGS will be to get the customers more ready to accept and utilize the CSEM data more eectively.”