Time‐lapse crosswell seismic tomography to characterize flow structure in the reservoir during the thermal stimulation

Abstract

Time‐lapse crosswell seismic tomography data, recorded with an interval of six months, indicate a strong directional thermal response in a fractured eolian sandstone reservoir at a five‐spot thermal stimulation site in the South Casper Creek oil field, Wyoming. The seismic thermal response depicted on the tomogram and in conjunction with the geological data from cores and a wireline log, reveals the multichannel flow mechanism in the reservoir formation. The three factors that control steam or heat propagation are the fractures, the directional permeability existing in the rock matrix, and the fault. Crosswell tomograms imply that the primary fluid flow is through fractures oriented north‐south, whereas the secondary fluid flow is through the matrix in the direction of maximum horizontal permeability. The thermal response expressed on the tomogram infers that a fault oriented N80°E offsets flow units and acts as a flow barrier or baffle. The flow structure implied by the crosswell seismic tomography is strikingly different from the initial conjecture, as deduced from engineering perception based on geological reasoning. However, the tomographic implications were supported by both a tracer test and fluid temperature measurements at the four producing wells around the injector.