Rapid inverse modeling of pressure interference tests using trajectory-based traveltime and amplitude sensitivities

This paper presents an efficient trajectory-based approach to integrate transient pressure data into high-resolution reservoir and aquifer models. The method involves alternating traveltime and peak amplitude matching of pressure response using inverse modeling and is particularly well suited for high-resolution subsurface characterization using hydraulic tomography or pressure interference tests. Compared to traveltime inversion only, our proposed approach results in a significantly improved match of the pressure response at the wells and also better estimates of subsurface properties. This is accomplished with very little increase in computational cost. Utilizing the concept of a "diffusive" time of flight derived from an asymptotic solution of the diffusivity equation, we develop analytical approaches to estimate the sensitivities for traveltime and peak amplitude of pressure response to subsurface properties. The sensitivities are then used in an iterative least squares minimization to match the pressure data. We illustrate our approach using synthetic and field examples. In the field application at a fractured limestone formation the predominant fracture patterns emerging from the inversion are shown to be consistent with independent geophysical experiments and borehole data.