Reservoir Induced Seismiciby Services

During hydraulic fracturing, frack fluid, consisting primarily of water with chemical additives, is pumped into a geologic formation at pressures up to 15,000 psi. The high pressure of the fluid, which is designed to exceed the rock strength, opens or enlarges fractures that can extend several hundred feet away from the well. After the fractures are created, proppants in the fluid are pumped into the fractures to keep them from closing when the pumping pressure is released. After the fracturing is completed, the downhole pressure of the geologic formation causes the injected fracturing fluids to rise to the surface where it is typically stored in tanks or pits prior to disposal or recycling

The technique of hydraulic fracture monitoring usually involves deploying a geophone array in a borehole, at or near reservoir depth end. The array of three-component geophones records any induced seismicity occurring within the reservoir. LandTech installs in addition to the borehole sensors and a dense grid of specially designed surface sensors in order to obtain a better 3D velocity model and increase the location accuracy of the induced microseismic events. Recently it has developed very sensitive surface sensors which eliminate the necessity to use monitoring wells, thus reducing considerably the monitoring cost.

Microseismic events are small earthquakes occurring on failure surfaces (e.g. fractures) which have radii of around 10m. Stresses acting on a rock mass are anisotropic, so shear stresses build up on fracture surfaces. Under normal conditions these fracture surfaces are locked. However when the on site stresses are perturbed by reservoir activity, such as changing fluid pressure, the fractures shear producing small earthquakes. The seismic signals from these microearthquakes (also known as microseismic events) can be detected and located in space using geophones. This means that mapping the microseismic events is the same as mapping the location of pressure/stress changes within the reservoir.

Benefits of LandTech’s Fracking Monitoring:

• Higher level of detection sensitivity
• Much less cost due to no need of monitoring well
• Very adjustable since the monitoring network can move to various regions of the reservoir
• Real time monitoring
• Better location of events since a 3D seismic ray geometry is used instead of a 1 dimensional ray geometry
• Also a 3D velocity model is used which farther improves the event location accuracy
• Reduced environmental impact
• Improved efficiency