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DTU Olie og Gas
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smart water as lubricant ?e scientific work with the ct scans focuses on examining which eor
method
s might be worth using in or- der to improve the sweep efficiency and reduce the residual
oil
saturation in an
oil
field. ?it?s much easier to choose the best eor
method
when you can see what is happening inside the chalk and at the same time measure how much
oil
comes out. if you only measure the
oil
, it?s like working in the dark,? says an- ders nymark christensen, a postdoc at dhrtc. initially, the scientists are focusing on different combinations of brine as an eor
method
? so-called ?smart wa- ter?. ?e researchers? hypothesis is that it would be cheaper for the industry to use a variant of water rather than add- ing various chemicals. ?e price has to be low, as the
oil
industry will need to use huge volumes. in 2014, about 35 million cubic metres of sea water were injected into the rocks under the north sea as part of the work to recover
oil
,? explains anders nymark christensen: ?so, even if, as part of eor, you needed to add just 100 ml of a chem- ical, for example, to one cubic metre of water, it would still add up to large quantities,? he says. ?e two researchers are part of an ever-growing team of more than 10 people who are trying to find eor
method
s that can increase
oil
recov- ery, particularly in the north sea. "we are working to make sure that the improvement in production will be significant, ideally around 10 per cent or more of the original
oil
in place in the laboratory," explains amalia yunita halim, who adds that the work in the laboratory is associ- ated with a degree of experimental uncertainty. ?erefore, the results cannot be translated directly to the north sea. challenges along the way it has taken a lot of patience to improve the
method
, which the researchers are expecting to describe in scientific journals. ?e challenges have included: ? selecting representative
core
samples, so that comparable tests can be car- ried out in both the ct scanner and in similar setups without ct scanning ? analysing and using water with the same composition of salts as is found in the
oil
reservoirs in order to have the right reservoir condi- tions in the laboratory ? working with a medical scanner that gets hot during the process and thus affects the test so that data had to be ?cleaned? a?erwards ? developing a
method
for working without contrast agent, which is normal with ct scans. ?e usual contrast agents bind to the chalk and produce poor results ? developing
method
s for synchro- nizing the images from the scanner (i.e. combining several images to produce a single image) and filter- ing them in a resolution that pro- vides true quantitative information. ?e development work also de- manded considerable innovation along the way. for example, anders nymark christensen found out that, by drill- ing millimetre-wide holes in the
core
samples, he could use the holes to syn- chronize the images. at the end of 2016, the status is that the
method
has been validated. among other things, this is evident from the fact that the saturations from the image analyses from the ct scans are consistent with the mass balance. ?in other words, we now know what we inject, we know what happens in- side the
core
sample, and we know what comes out. ?is means that we?re ready to start testing different eor
method
s,? says anders nymark christensen, and the two researchers agree that the really interesting part of the work can now begin: ?our work only becomes really in- teresting once we find an eor
method
which can actually lead to greater
oil
recovery in the danish section of the north sea,? says amalia yunita halim. 17 dhrtc 2016 alternative
method
s for water flooding experiments at the end of 2016, researchers at the geologi- cal survey of denmark and greenland (geus) started a series of ?ekofisk base case experi- ments?, with the aim of investigating alternative
method
s for water flooding under reservoir conditions in the laboratory. in such experi- ments,
oil
recovery in the north sea is simulat- ed under conditions which are as close to reality as possible. one of the challenges today is that the process takes three to four months for each chalk
core
plug. can it be done faster? geus will examine this by comparing the usual porous plate technique for saturating
core
plugs using water with the vapour saturation
method
. ??eoretically, the porous plate technique is the most correct for simulating what happens in the reservoir, but the evaporation saturation
method
is much easier and quicker to use. so, if we can validate that it can be used without any disadvantages, it will be preferable,? says dan olsen, senior researcher and head of the geus
core
laboratory. geus is also examining whether you can use ?dead crude
oil
? ? i.e.
oil
which is degassed ? instead of ?live crude
oil
?, which contains the naturally occurring gases, without impacting the quality of the measurements of the
oil
re- covery. it is faster, easier and cheaper to work with degassed
oil
. in addition, geus is examining: ? what difference there is in the results depend- ing on whether
core
plugs are used which are fractured or not. the study may be able to improve the computer modelling of flow in fractured
oil
reservoirs. ? whether the
core
plugs can be reused in ex- periments without it affecting the quality of the results. it would be an advantage if they could be reused, as it is expensive and difficult to obtain
core
plugs from
oil
reservoirs in the north sea. ?e ekofisk base case experiments are expected to be completed by mid-2018.
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