Abstract
In 2003 a permanent seismic array, LoFS, was installed in across the Valhall field in the North Sea. Since then fifteen seismic surveys have been acquired. The main objective of the Valhall LoFS system is to support the water flood programing which started in 2006 and are is expected to deliver 30% of the remaining resources in the field. To date15 seismic surveys have been acquired and the LoFS program has proved to deliver valuable information, which is also underpinning the delivery of a safe and reliable continuous drilling program.
The Valhall field has been on production since 1982 and produced in excess of 800 mmboe since field start-up. The primary reservoir is the over-pressured, high porosity and fractured Upper Cretaceous Tor formation. The field is compacting during depletion, resulting in subsidence in the overburden.
In monitoring of the Valhall water-flood program we were facing several fundamental technical challenges which not necessary favor a seismic based surveillance; poor p-wave seismic quality in part of the field and the presence of very thin dense, zones with pervasive fault induced fracturing which act as fast conduits for fluid in a low permeable reservoir.
Fortunately, the type of seismic recordings achieved using a system like the one installed at Valhall turned out be favorable for the use of full waveform inversion (FWFI) to produces detailed and accurate velocity models which has significantly reduce the area impacted by poor seismic definition. These velocity models greatly complement existing reflection data, and have also been very helpful for the delivery of new wells in a complex overburden.
FWFI is one of several technology developments which have helped us making the permanent monitoring of the Valhall field as significant technical success.
Biography
Olav Inge Barkved is currently an Advisor in Geophysics with BP, located in Stavanger, Norway, where he has been supporting the development of the Valhall field as a geophysicist, technology coordinator and team lead. From 2003 to 2008 Olav was the project leader of the Valhall Life of Field Seismic delivery program. In 2006 he received the Norwegian Geophysical Award for his technical contribution and ability to identify and implement emerging technologies to support business objectives in support of field development. BP's Valhall Life of Field Seismic Project has been recognized by the industry by receiving the Norwegian Petroleum Directorates Improved Recovery award, the ONS innovation award and OTC's Distinguished Achievement Award.
Olav receiving his MSc in Oil and Gas exploration from the Norwegian Institute of Technology in 1983, he started working as a Research Scientist with Geco, working a variety of aspects related to seismic reservoir characterization, interpretation technology and processing. His career with Geco, included stays at Schlumberger Doll and Schlumberger Cambridge research. In 1992 In 1992 Olav joined Amoco, and remained through the merger with BP in 1998.
Olav has, together with his colleagues, received the EAGE best paper award in 1997 and in 2009, the Louis Canard Award in 2008 and TLE best paper award in 2008. Olav is a member of NGF, NPF, EAGE and SEG and served as an EAGE Distinguished Lecturer in 2010.
