Seismic imaging of reservoir flow properties: Resolving water influx and reservoir permeability

Abstract

Methods for geophysical-model assessment — in particular, the computation of model-parameter resolution — indicate the value and the limitations of time-lapse data in estimating reservoir flow properties. A trajectory-based method for computing sensitivities provides an effective means to compute model-parameter resolution. We examine the common situation in which water encroaches into a reservoir from below, as caused by the upward movement of an oil-water contact. Though the techniques described are not limited to this case, we treat the situation in which the time-lapse response is primarily caused by changes in saturation. Using straightforward techniques, we find that, by including reflections off the top and bottom of a reservoir tens of meters thick, we can infer reservoir permeability based upon time-lapse data. We find that, for the case of water influx from below, using multiple time-lapse snapshots does not necessarily improve the resolution of reservoir permeability. An application to time-lapse data from the Norne field in the North Sea illustrates that we can resolve the permeability near a producing well using reflections from three interfaces associated with the reservoir.

A feasibility study of land CSEM reservoir monitoring in a complex 3-D model

“…Smaller effects may be caused by changes in the near surface. A central question in EM monitoring is whether or not resistivity changes in the reservoir are detectable, and if so, if the value of that information is worth the effort compared to more established methods as time‐lapse seismic measurements (Landrø et al 2003; Vasco et al 2008) that provide far better resolution, but not necessarily of the same quantity. In the EM case, spatial resolution will always be poor due to the diffusive character of EM signals in the earth at the low frequencies required to reach sufficient depth (Ward & Hohmann 1987).…”

The feasibility of reservoir monitoring using time-lapse marine CSEM

“…The objective of reservoir-depletion monitoring is to determine the efficacy of the extraction and enhanced oil recovery ͑EOR͒ processes. The current approach to geophysical monitoring of reservoir depletion is to use time-lapse 3D seismic technology ͑e.g., Landro et al, 2003;Vasco et al, 2008͒, an approach that is in the early stages of development. If the feasibility of applying CSEM to this application is demonstrated, we anticipate that CSEM will prove to be highly complementary to time-lapse seismic data, as is the case with exploration CSEM ͑e.g., Darnet et al, 2007͒.…”

Controlled-source electromagnetics for reservoir monitoring on land

“…Smaller effects may be caused by changes in the near surface. A central question in EM monitoring is whether or not resistivity changes in the reservoir are detectable, and if so, if the value of that information is worth the effort compared to more established methods as timelapse seismic measurements (Landrø et al, 2003;Vasco et al, 2008) that provide far better resolution, but not necessarily of the same quantity. In the EM case, spatial resolution will always be poor due to the diffusive character of EM signals in the earth at the low frequencies required to reach sufficient depth (Ward and Hohmann, 1987).…”