Tomographic Fracture Imaging (TFI): Direct 5D Mapping of Transmissive Fracture/fault Fairways Using Seismic Emission Tomography (SET)

Abstract

TFI is a proven method for direct 4D mapping of transmissive fracture/fault networks with over 50 successful projects completed for the Oil and Gas industry. TFI uses SET to capture the weak but spatially and temporally coherent seismic emissions of transmissive fracture/fault damage zones. TFI works by utilizing two phenomena of the Earth¡¯s brittle crust. 1. The near critical state where stress drops ¡Ü 0.01 bar are associated with failure. 2. Fluid pressure (Pf) waves created by changes in Pf that propagate through transmissive networks for distances that can be at the kilometer scale and at velocities of 10s of meters/second. TFI differs from hypo-central techniques in two ways: 1. It can extract objective images of the actual fracture/fault surfaces themselves thus eliminating the need for the highly subjective interpretation of hypo-central clouds. 2. It uses high sampling rates (1ms) and stacking rather than standard hypo-central location techniques. Stacking from seconds to hours allows the signal of the weak seismicity of the fracture damage zones to emerge. TFI has proven X,Y accuracy of as much as +/- 5m. In all cases (>20) where independent evidence for the location of transmissive fracture/faults existed, TFI results were confirmed. We give the geological and geophysical framework for TFI. As an example of TFI we show a movie sequence of 1 minute intervals during which a Pf wave induced by a frac moved along a natural transmissive fairway to intersect a 2nd well over 700 m from the treatment well. The Pf wave preceded the arrival of the fluid in the well intersected by the fairway by 2 stages.