TNO Acquires High Resolution 3D Seismic Data of P18 Gas Field

TNO has acquired high resolution 3D seismic survey to image the shallow water overburden above the P18 gas field. A high-resolution 3D seismic survey is an innovative combination of technologies that resulted in a very high resolution 3D image of the shallow subsurface above the P18 gas field.

In April this year, the RV Pelagia left its Port in Den Helder for a 3D seismic survey near the P18 gas field. With this survey TNO combined shallow high resolution seismic profiling, traditionally only carried out in 2D, with the 3D seismic acquisition that is used for deep oil and gas exploration. The result is a high resolution 3D seismic image of the shallow subsurface, at relatively low cost.

The rock formations of the nearly depleted gas field offshore Rotterdam are a potential site for storage of CO2 . In order to confirm that the storage functions as expected, it is important to accurately map the shallow subsurface – down to a depth of around 1.5 km, before operations begin. The crew on board included staff from Deltares, NIOZ and TNO. TNO was represented by geophysicist and project manager Vincent Vandeweijer. Funding for the survey came through CATO2, the Dutch national research programme on CO2 capture, transport, and storage.

SURVEY DESIGN

The TNO approach to the survey is unique as it combines two approaches that used to be incompatible in the past. “At first glance, this may look like business as usual,” says Vincent Vandeweijer with a big smile.

“But as far as we know, it is the first time ever that a survey has been acquired in this way. There were quite some challenges, such as devising and constructing some non-standard pieces of equipment, the design of the survey’s data acquisition geometry, as a well as all the operational planning on a tight schedule. ConocoPhillips, the US oil and gas giant was interested in our approach. As one of the leaders in innovation of seismic data-acquisition and processing technology they saw an unique opportunity to test some of the ideas the company has been developing recently. They decided to partner with us and their operational knowledge contributed greatly to the project’s success.”

COVERAGE

In a 2D survey a streamer cable with acoustic sensors (hydrophones) is towed behind the stern of the vessel. Surveying in a 3D geometry implies towing multiple cables and requires a vessel with a wide rear deck.

Vandeweijer said: “We found a way to deploy the seismic sources and cables with a wide spread, using extension rods the length of lampposts. In addition, we were able to demonstrate that a seismic source can be towed a couple of hundred meters behind the vessel, which improves data coverage at no additional cost. During operations we did a bit of quick data processing on board. We can already say that we have collected a unique 3D dataset in high resolution. Once the processing has been completed, we will be able to visualize the subsurface in 3D and study all kinds of features in detail. For instance, we expect to be able to find out where there are faults and if there are gas accumulations. As a bonus, we can also generate highly detailed acoustic images of the seafloor.”

SINK OR SWIM

The 3D seismic survey can serve as a base line survey of the area. “Suppose that CO2 is stored in the P18 gas field; the survey can be compared with additional surveys at later dates to confirm that there is no leaking of CO2 towards the sea bed. With our new approach we will be able to bring the cost for a 3D seismic survey down to about a fifth of what a 3D survey for a deep target would cost, which is also very interesting for exploration for shallow gas reservoirs.”

Vandeweijer is satisfied: “It’s always sink or swim when you are out to sea. You have to be on alert 24 hours a day and handle unexpected situation, using nothing else than your creativity and the tools and hardware you took with you on board. You cannot possibly be prepared for every situation when you are testing something that has not been done before. As always, it was both enervating and rewarding at the same time.”