Fluid is pumped through long boreholes drilled from surface to create hydraulically-induced fractures. These fractures increase the permeability of the rock mass, enhancing the flow of oil/gas up boreholes to surface. Microseismic monitoring can be used in real-time to image the new fractures, improving control and efficiency while lowering total cost of the project. The sensors are temporarily installed into long cased boreholes for fracture monitoring, and the seismic station at the surface transmit data in real-time to a local central site. A custom GPS receiver is used for sub-microsecond time synchronisation.
If the project is short-term and only a single monitoring well is used, IMS supplies a temporary shelter for both the seismic data acquisition equipment as well as the central site at the top of the well. If more than one well can be used, or a permanent 4D monitoring is being deployed, then the seismic station at the top of each well uses WiFi to digitally communicate with the remote central site.
Downhole seismic arrays are used for recording the seismogram data. The sensors are typically IMS 14Hz tri-axial geophones, rated to 20 bar/2000m depth. The sensors are temporarily deployed using a borehole clamping mechanism.
SEISMIC DATA PROCESSING & INTERPRETATION
The processing of seismic data is real-time, and delivers an up-to-date map of where fractures are being created. The source mechanisms are also obtained, allowing the well engineer to see what type of fractures are taking place at each location.