TIME-LAPSE JOINT INVERSION OF CROSS-WELL DC RESISTIVITY AND SEISMIC DATA: A NUMERICAL INVESTIGATION

Abstract

Time-lapse joint inversion of geophysical data is required to image the evolution of oil reservoirs during production and enhanced oil recovery, CO2 sequestration, geothermal fields during production, and to monitor the evolution of contaminant plumes. Joint inversion schemes reduce space-related artifacts in filtering out noise that is spatially uncorrelated while time lapse inversion algorithms reduce time-related artifacts in filtering out noise that is uncorrelated over time. There are several approaches that are possible to perform the joint inverse problem. In this work, we investigate both the Structural Cross-Gradient (SCG) joint inversion approach and the Cross-Petrophysical (CP) approach, which are both justified for time-lapse problem by petrophysical models. In the first case, the inversion scheme looks for models with structural similarities. In second the case, we use a direct relationship between the geophysical parameters. Time-lapse inversion is performed with an actively time-constrained (ATC) approach. In this approach, the subsurface is defined as a space-time model. All the snapshots are inverted together assuming a regularization of the sequence of snapshots over time. First we show the advantage of combining the SCG or CP inversion approaches and the ATC inversion by using a synthetic problem corresponding to cross-hole seismic and DC-resistivity data and piecewise constant resistivity and seismic velocity. We show that the combined SCG/ATC approach reduces the presence of artifacts both with respect to individual inversion of the resistivity and seismic datasets as well as with respect to the joint inversion of both data sets at each time step. We also performed a synthetic study using a secondary oil recovery problem. The combined CP/ATC approach is successful in retrieving the position of the oil/water encroachment front.