An estimation method for effective stress changes in a reservoir from 4D seismics data

Abstract

Advances in seismics acquisition and processing and the widespread use of 4D seismics have made available reliable production‐induced subsurface deformation data in the form of overburden time‐shifts. Inversion of these data is now beginning to be used as an aid to the monitoring of a reservoir's effective stress. Past solutions to this inversion problem have relied upon analytic calculations for an unrealistically simplified subsurface, which can lead to uncertainties. To enhance the accuracy of this approach, a method based on transfer functions is proposed in which the function itself is calibrated using numerically generated overburden strain deformation calculated for a small select group of reference sources. This technique proves to be a good compromise between the faster but more accurate history match of the overburden strain using a geomechanical simulator and the slower, less accurate analytic method. Synthetic tests using a coupled geomechanical and fluid flow simulator for the South Arne field confirm the efficacy of the method. Application to measured time‐shifts from observed 4D seismics indicates compartmentalization in the Tor reservoir, more heterogeneity than is currently considered in the simulation model and moderate connectivity with the overlying Ekofisk formation.

Practical Applications of Time-lapse Seismic Data

“…To address this need, Garcia et al (2010) take advantage of a geomechanical simulator that can model a complex subsurface. They propose that the relationship between the reservoir pressure change and the overburden strain can be considered to be a linear filter Downloaded 09/30/15 to 129.78.139.28.…”

“…They propose that the relationship between the reservoir pressure change and the overburden strain can be considered to be a linear filter Downloaded 09/30/15 to 129.78.139.28. If the reservoir does not behave as a linear elastic solid (e.g., as a com pacting chalk or an HPHT reservoir), the method can be used to invert for reservoir volumetric strain which, assuming there is no fault movement, is always lin early related to the overburden strain (Garcia et al, 2010). In this context, the Green's function is a filter transfer function.…”

“…Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/ process. Garcia and MacBeth (2013) have applied that method to 4D data from the South Arne chalk field in the Danish North Sea. Garcia et al (2010) use the simulator to calculate the Green's functions that are generated from a selected number of pressure sources (e.g., in separate pressure compartments).…”

“…In this context, the Green's function is a filter transfer function. Garcia et al (2010) comment that with this method, we can easily apply the filter in both forward and inverse directions. A spatially varying filter is then estimated from the Green's functions, and the inverse of that filter is used to predict reservoir pressure changes from measured overburden strain.…”

Adaptive scaling for an enhanced dynamic interpretation of 4D seismic data

“…For the synthetics considered below, this is achieved by using picked horizons common to both data sets. For the observed data this is performed using a code based on the work of Hale (2007) as implemented by Garcia and MacBeth (2011), which employs the cross-correlation based technique. Both 4D seismic maps are consistent with the general well activity ( Fig.…”