16 EXPLORATION/DRILLING/FIELD SERVICES
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measured. Instead, engineers infer geologic properties indirectly from seismic data and measurements taken at scattered wells. “In a typical reservoir, millions of pixels are needed to adequately describe the complex subsurface pathways that convey the oil to wells. Unfortunately, the number of seismic and well observations available for estimating these pixel values is typically very limited. The methods we’ve developed extract more information from those limited measurements to provide better descriptions of subsurface pathways and the oil moving through them,” said McLaughlin, lead researcher on the project. In a 36-month simulated oil-recovery process, McLaughlin and Jarfarpour’s estimation approach accurately captured the main features and trends in fluid conductivity of a reservoir formation, demonstrating that the new technique is robust, accurate and efficient (Fig. 1). “Our next step – already in progress – is to test our
idea in real oil reservoirs and evaluate its impact on oil recovery under realistic field settings,” Jafarpour said.
Meanwhile, new Danish research may have come up with an explanation as to where and how North Sea oil clings to underground rocks. This explanation could turn out to be the first step on the way to developing improved oil production techniques with the intent of increasing oil production from Danish oil fields. A research group at the Nano-Science Centre,
part of the Institute of Chemistry at University of Copenhagen, has investigated drill cores collected from North Sea oil fields using an atomic force microscope.
Their investigations show that the spaces which contain oil have totally different surface qualities than expected from our knowledge of the minerals which make up the rock. The rocks which contain oil in the
Danish part of the North Sea are primarily chalk – the same type of rock that the cliffs of Stevns and Møns in Denmark are made of. Assistant Professor Tue Hassenkam led the
research, whose preliminary results were published in Proceedings of the National Academy of Sciences (PNAS) in June. He says that this is the first time that investigations of this type have been carried out on chalk from an oil field in the North Sea. “Previous investigations were carried out on the
surface properties of pure mineral crystals. But our investigation has shown that this chalk has a different and more complex structure,” says Hassenkam. The oil bearing layers in the subsurface are
reminiscent of a sponge. The oil ‘hides’ in tiny pores and gaps and only some of the oil can be pressed out of the chalk and into the borehole by injecting water into the chalk layer. The rest is left behind as small droplets of oil surrounded by water either in small gaps in the rock or stuck to the walls of the pores. The chalk particles ought to repel oil if they act like particles of the mineral calcite, which chalk is almost 100 per cent made up of.
However the new investigations, carried out with
a particularly powerful microscope, have shown that the surfaces of the pores in the chalk are partially covered in a material which oil can stick to. Hassenkam believes that the surprising behaviour of the material in the surface of the chalk can be explained by studying how the chalk was formed. “Chalk is actually the casings of ancient algae. The algae gave their cases a type of ‘surface coating’ to make them resistant to water. And it is probably this surface coating that we can see in action here, even 60 million years later.”
For two years now Mærsk Oil and Gas and the Danish National Advanced Technology Foundation have been supporting a closely-related project: the Nano-Chalk Venture. o
ENCODER FEATURES REPLACEABLE SHAFT
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