9345765574

Doc. No.

Snohvit C02 Tubaen Fm. storage capacity and inj«ction strategy study

Valid from

Rev. no. 1.0

We expect challenges related to CO; injection at Snohvit to remain, and the need for dedicated reservoir management to make surę the reservoirs and wells have sufficient capacity to remain for the next several years. In that perspective, we recommend to acquire new seismic monitor data every second year. This will also fulfil the Klima- og forurensningsdirektoratet (Klif)’s reguest for monitoring and assurance that the site is not leaking.

5.4 Passive seismic (microseismic)

Fracturing often causes smali earthquakes (acoustic events) to occur, and passive seismic registrations - with sensors on the surface or in boreholes may be used to determine when fracturing occurs, as well as event locations and source mechanics. This gives much richer information on the fracturing process than is otherwise available (e.g.    b). It can potentially determine whether fracturing is confined to the reservoir or enters into

the overburden, and it may give the temporal response to a well pressure increase indicating whether the movement is tensional or shear. There is a maturę commercial market for microseismic monitoring of hydraulic fracturing using water, and such monitoring has also been used in the Weyburn CO; project (    ).

concluded from a field comparison of water and CO; injection that the microseismic signature is expected to be fairly similar for the two injection fluids, and thus the large experience on water injection is relevant also for CO? injection. Microseismic monitoring has also been recently implemented at the In Salah C02 storage site (    ), with around 40 events recorded, and is currently being analysed by

several specialist groups, including Engineering Seismology Group.

In Longyearbyen, a test well was drilled late 2009, and during a water injection test carried out February 2010 microseismicity was recorded with one 3C geophone in a borehole 45 m away from the injection well, at a depth of 300 m - about 600 m above the open hole section subject to injection test. The test interval within the Triassic Kapp Toscana Group, is time equivalent to Tubaen Fm. Analysis of the microseismic data is currently ongoing at NORSAR, which has reported 1911 events in about three days, many at considerably shallower depths than the

injection zonę (Figurę 90), and with some alignment along a SW-NW trend.

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Figurę 90: Preliminary microseismic event location from Longyearbyen water injection test February 2010. Data analysis provided by NORSAR.

Classification: Intemal Status: Draft Expiry datę: 2012-12-31 Page 1 1 3 of 132