Improving Oil Recovery from Chalk Fields

Professor Tor Austad at the University of Stavanger was recently awarded the Norwegian Petroleum Directorate’s 2010 IOR prize for his research in getting more oil out of chalk fields. His work will be crucial in keeping production from these types of fields in the Norwegian shelf until 2050 and beyond.

Facts

Previous Norwegian Petroleum Directorate Prize Winners

1998 Hydro for drilling of horizontal wells near the oil-water contact in the Troll field to produce more oil from the thin oil leg.

1999 Saga for Foam assisted Water alternating Gas injection, FAWAG –pilot in the Snorre field.

2000 Phillips Petroleum for making decisions on IOR/EOR projects in the Ekofisk field even when the oil price was low.

2001 Statoil and Egil Sunde for the use of bacteria, MEOR, in the Norne field.

2002 No worthy candidate found.

2003 BP for “Life of Field Seismic” project in the Valhall field.

2004 Gullfaks license for project decisions and implementation ranging from advanced drilling into new reservoirs to new methods of produced water treatment.

2005 Arne Skauge, Prof at UiB/CIPR, for his success to bring IOR research from laboratories to pilot testing and implementation in fields and for his educational skills.

2006 Halliburton and Baker for developing well technology needed in the Troll field.

2007 Talisman for courage and willingness to operate fields at tail end to prolong the production – specially mentioned Yme field re-development.

2008 No worthy candidate found.

2009 FMC Technologies for having demonstrated the courage and determination to invest in technology that increases production from seabed wells.

Source: Norwegian Petroleum Directorate

Austad received the prize this June, together with the Corec research centre at IRIS in Stavanger, for research that has helped oil companies understand the reservoir recovery mechanisms for the chalk fields in the southern part of the North Sea.

He has spent the last two decades studying the special properties of seawater as an enhanced oil recovery and compaction fluid in chalk reservoirs with a high temperature. This has helped explain why injection of seawater displaces oil so efficiently on Norway’s Ekofisk field in the southern North Sea.

His research also helped clarify the chemical mechanism for weakening chalk rock with seawater. This is expected to have considerable significance in the work to improve the efficiency and lifetime of the wells in the area, according to the Norwegian Petroleum Directorate (NPD).

Seawater injection at Ekofisk
Austad’s work with Corec began in 2002 after the NPD requested operators to increase the oil recovery rate on their fields to 50%. The average at the Ekofisk field was 46%, among one of the highest on the shelf. Phillips, operator of the Ekofisk field, started a co-operation with the University of Stavanger and IRIS that later became the Corec programme.

“It was very astonishing to me that you could have such a high recovery (at Ekofisk),” said Austad. He began to think seawater must have some kind of special effect.

The reason Phillips was injecting seawater into the reservoir originally was to re-pressurize the reservoir. The field was producing below the bubble point of the oil and hence producing a lot of gas, which could empty the reservoir for drive energy. The NPD pushed Phillips to run a pilot project and see how seawater injection would function, not knowing at that point seawater was able to imbibe into the rocks matrix.

“At that time it was very gambling,” recalls Austad. ”The experience in the Middle East showed water was not able to displace oil in the matrix.”

The general problem with chalk and other carbonate fields is that oil absorbs into the rocks – similar to a sponge. That makes it difficult for water to soak into the matrix block and displace the oil.   

His research found that seawater changed the rocks’ wetting properties. It was able to release organic material from crude that was absorbed onto the rock. That enabled oil companies to get more water closer to the rock’s reserves and increase the capillary forces to improve recovery.

He discovered that the formation water in the reservoir – i.e. the initial water mixed with oil – had different composition compared to seawater. The key difference was sulphate, which is found in seawater but not in formation water. This was responsible for changes in the wetting properties.

International Recognition
Austad’s work with wettability properties of chalk in Norway has gained international recognition. It has for example been applied for carbonate fields in the Middle East. He is working with international oil companies in Abu Dhabi and Saudi Arabia and seawater is piped from the Arabian Gulf to onshore fields in the desert to help pump out more oil from their fields using water injection.

In addition, he has started research on water-based enhanced oil recovery (EOR) for other carbonates such as limestone and dolomite and received support to study wettability properties in sandstone reservoirs with a special focus on low salinity flooding.

He also contributes to the International Energy Agency on improved oil recovery, along with Norwegian researcher Arne Skauge. The two are scheduled to attend this year’s workshop in Vienna in October.

Professor Tor Austad and the Corec research centre at IRIS were honoured for the important research carried out on oil recovery from chalk fields.

The Corec research centre, with which Austad shares the NPD prize, has been working with improved recovery since 2002. The centre is a collaborative project between the Univeristy of Stavanager, the IRIS research foundation, and ConocoPhilips as the operator of Ekofisk, Eldfisk and Tor. The NPD highlighted in this year’s IOR prize in particular Corec’s work investigating the effect of injecting CO2 following water injection in chalk fields.

“The potential for improved recovery with use of CO2 is undoubtedly large,” said Bente Nyland, NPD director general, in June. “At the same time, the integrity and stability of the chalk rock is a challenging question if CO2 is injected.”

The project is planning for a new nine-year period, starting in the autumn, where they will continue the work on improving understanding of water injection, as well as examine the use of CO2 injection and microbial recovery from carbonate fields.

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