FRANCE: Joint studies laboratory researches through-reservoir fluid transfer

Oil companies, service contractors, and European academic institutions will shortly begin the joint investigation of fault mechanics and their relationship with fluid flow and earthquakes. Three separate studies are being performed at a laboratory on the south shore of the Corinth rift, near Aigeon in Greece. This is said to be Europe's most seis-mically active zone. The studied faults affect Cretaceous carbonate rocks, which constitute a classical fractured hydrocarbon reservoir.

Continuous monitoring of strain, seismicity, fluid pressure, and geochemistry will be conducted at the surface and at various depths in boreholes intersecting active faults. Well imaging will be performed repeatedly through the boreholes to study the fractures and their connection with stress variations. The laboratory, which has been established with European Union funding, spans an area of 30 sq km, and features:

• Four wells, 500-1,200 meters deep, on active faults
• Several shallow wells for strain, stress, and fluid flow monitoring
• A surface array of accelerometers, GPS, and seismic stations.

One of the projects, coordinated by the Institut Français du Pétrole (IFP), is aimed at improving understanding of fluid transfer in and around fault zones and through carbonated reservoirs. Data collected through stress, strain, fluid core, and borehole imaging should aid fault hydraulic and mechanical behavior analysis and will also lead to calibration of all the team's tools on fractured reservoirs, especially through comparing the opening of the fracture with the stress field.

Various sub-groups will be working together. IFP, Enterprise Oil, and the Institut de Physique du Globe de Paris (IPGP) will be examining the damaged zone around the fault by increasing the cored section to 200 meters. Different tools will be employed to describe the material's anisotropy (DSI, FMI, VSP, local seismic network).

The current theory correlates anisotropy with the stress field, so further stress measurements will be made in the wells and the surrounding area. A small 3D survey will also be shot around the well on a surface geophone array. IFP, Schlumberger, and GeiForschungsZentrum Potsdam will test two new technologies for permanent monitoring captors:

• One based on fiber optics to record strain variation versus time (to be installed in the deepest well)
• One based on cemented electrodes - a special well will be dedicated for monitoring flow of the conducive fluid along the fault plane

With Rome's Istituto Nazionale di Geofisica (ING), IFP will also sample fluid flow in all the wells and will conduct chemical description for a short, continuous period. Measurements will include noble gases (ratio and isotopes) in order to understand the source of these elements. Well fluid, cement and paleofluid compositions will be correlated through modeling the fluid/rock interactions.

Another multinational group involving IFP will work on geomechanical modeling of the data to better define the rock deformation and fluid flow in faulted and fractured material. They will also attempt to show potential synergies between the geomechanical approach (employed by academic institutions) and large-scale fluid flow, as adopted by the oil industry.