The Use of Seismic Emission Tomography (SET) for Imaging Hydraulically Linked Fracture/Fault Networks of Hydrocarbon Reservoirs

Peter Geiser¹, Jan Vermilye¹, Robert Scammell², and Steve Roecker^3
1 STRM LLC, Boulder, CO
² Burlington Resources Canada Ltd, Calgary, AB
³ Rensselaer Polytechnic Institute

We present a method for direct imaging of the fracture scale geometry of reservoir permeability fields using surface based seismic networks. The method makes use of the near critical state of the earth's crust, such that small (≤ .01 bar) perturbations of the ambient stress field are sufficient to cause failure of critically oriented cracks. We find that such perturbations can be generated by a fluid pressure (Pf) “wave” initiated by any &DeltaPf such as that generated during a flow test or frac. The phenomena may be a manifestation of the Biot “slow wave”. Wave velocity appears to be on the order of m/sec, while its effects extend for distances of kilometers from the point of &DeltaPf. Because the ambient permeability field consists of critically oriented cracks, passage of the Pf wave causes their failure. SET methods are used to process the weak acoustic energy (AE) emissions of the failure events illuminating the geometry of the ambient permeability field. The SET results are presented as a sequence of time stacks of the AE energy field in a contoured voxel format. The fracture/fault networks appear as transient energy events occurring in locations geographically stable over some time interval. Crack propagation theory is used to analyze and further process these data to produce 3D skeletons of the permeability field geometry. We illustrate the successful application of the technique in two tight gas plays where we interpret the results as the first direct images of the 3D geometry of reservoir permeability fields.