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Areal monitoring of the reservoir

Thursday, January 31, 2013

Shell is developing ways to make it easier and faster to implement permanent reservoir monitoring systems

Take-up of reservoir monitoring solutions is still slow, mainly due to cost, says Peter Engbers, Smart Fields and Areal Reservoir Surveillance Global Deployment Lead with Shell, and a past Head Quantitative Seismic Interpretation at Brunei Shell Petroleum.

Technologies for monitoring reservoirs while they are producing, including 4D seismic and seabed fibre optic cable, have been available for many years.

But when it comes to seabed permanent fibre optic recording for areal reservoir surveillance, you can count the number of implementations 'on one hand', he reckons.

He was speaking at the Integrated Operations conference in Trondheim on September 25-26.

Shell uses the term 'areal reservoir surveillance', for monitoring reservoirs while they are producing.

But you can reduce the costs by keeping the reservoir monitoring systems over a smaller area of the seabed, where they can provide the most value, he says. 'We can focus on where it is needed,' he said.

'One obvious place is in a water flood, when we are injecting. We basically need to visualise what is happening around the injector, where is the water going.'

'We don't need to monitor the whole field if we are injecting in a few wells. We just have to monitor a few kilometres around it.'

Shell is developing ways to get a range of areal reservoir monitoring tools deployable in 5 months.

'The whole idea is to have a flexible system which we just put there when we need it,' he said.

Shell has a name for the system - 'i4D', which means 'Innovative, inexpensive, intelligent and instantaneous,' he said.

'We basically measure everything in an instantaneous way get the results within days on your workstation. That's more efficient, faster and cheaper. That's what we see as a future way for a lot of particularly water flood fields.'

'It's a real qualitative use of the 4D seismic data.'

So far Shell has 80 fields covered with different types of 4D seismic.
'That's about a quarter of all the fields in the whole of the Shell group,' he said.

'Most of them are already the fields where we think this is making sense. 'We are going very far to what we feel is our applicable base.'

'By the end of 2014 we will have covered all our offshore water flood fields with 4D seismic.'


Benefits

The biggest reason for areal reservoir surveillance is that reality is often different to what reservoir models predict. 'There are always unexpected things,' Mr Engbers said. The reservoirs all behave differently to our reservoir models.'

Where the 4D data has been gathered and integrated with reservoir models, the reservoir models typically show much more heterogeneity (mixed-up-ness), he said. 'So it is much more realistic and therefore much more accurate for helping position wells.'

Reservoirs might turn out to be a different shape to what was previously thought. 'We don't know much about how reservoirs will drain and how fluids will flow around them.'

By having a better understanding of the reservoir, you can improve your plan for where you want to drill wells in future. You can also use it to monitor how well any improved recovery methods are working (such as water flood) and see if they can be improved.

It can also help improve safety. 'More and more detailed information can tell us about unexpected fluid movements, maybe out of zone, out of zone fracturing or leakage of gas, and making sure we are injecting safely,' he said.

The information generated is useful to people working on a several month to several year time scale, who are in charge of well and reservoir management, and field development, he said.

Reservoir engineers usually do history matching, matching the actual data with the data the model predicted. But this is only usually done with production data, not reservoir data. If you continually monitor the reservoir, you can do history matching for the reservoir.

'Any areal data is automatically used to constrain your reservoir model,' he said.

It would be good if it could work on faster time scales, to support production optimisation and real time operations, he said, integrating the data with a dynamic reservoir model.


Technologies

Areal reservoir surveillance can involve a large range of different technology solutions, he said, but 4D seismic (taking repeated seismic surveys of the field to see what has changed) is 'the most specific and detailed way of working out what's happening there.'

Other methods include seabed fibre optic (see below), microseismic, passive seismic monitoring, borehole seismic measurements, time lapse magnetics, time lapse gravity, time lapse geodesy (small changes in the earth's shape). These can be used together with 4D seismic, or when 4D seismic doesn't work.

There are many developments with in-well fibre optic monitoring. Another method is time lapse geochemistry - taking chemical samples and analysing them. This can tell you something about how fluids or flowing around the subsurface, or your 'connectivity', he said.

'All of these solutions are deployed around the Shell group. And we are proactively pushing these out into more and more, even more remote places.'

'It makes sense to combine time lapse geodesy with microseismic or 4D seismic.'


Permanent reservoir monitoring

'One of the more advanced ways is to think not in terms of some individual surveys but to go to permanent reservoir monitoring,' he said.

'To install fibre optic lines or geophones on the seafloor, on land, and continously visualise and monitor what is happening.'

'These kinds of permanent systems make it possible to get repeatable and measurable 4D signals, being able to regularly repeat it and to make that very efficient.

Fibre optics on the seafloor can also measure seafloor geodesy, small changes in the shape of the seafloor due to oil and gas production beneath it.

'You can have a continuous and optimal measurement of your whole field and the overburden,' he said.


Slow take-up

'[But] one of the questions I always have, if [permanent reservoir monitoring] is the best thing in terms of surveillance, why is it not happening in the world?' he asked.

'Very few fields have these kinds of systems. We can count on one hand the number of worldwide installations.'

'One reason is the high upfront cost. But after that the opex [operating expenditure] is relatively low. So if you know you're going to do this a lot it would make sense to make this investment.'

'The challenge I want to give to you: why is the uptake so limited and how can we change that?' he said.

One possible reason for slow take-up is that the data from reservoir monitoring never makes it beyond the geophysics domain, when other departments in the company, particularly drilling, could do a lot more with it, once the field is in production.

'We in Shell are making sure it is all part of the bigger picture,' he said.

'Can we link this areal reservoir monitoring to integrated operations, to real time operations and production operations?'

'How do we make sure this is an automatic kind of piece of information that is being used, and tell you where you think this is going or where you have to make action?'



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