Time‐lapse tomography

Abstract

In time‐lapse analysis, we have to distinguish the seismic response changes due to oil and gas production at a reservoir over the years from several other causes, such as the recording signature and random noise. In this paper, we focus our attention on the velocity macromodel provided by seismic tomography, which is a basic tool for the data regularization, its depth or time migration, and a possible final subtraction among different vintages. We show first that we cannot use just a single velocity model for all data sets, because of seasonal variations of the overburden velocity (which is mainly due to seawater temperature in marine cases and to the water table depth in land cases). However, we can exploit the basic assumption of time‐lapse analysis for constraining reflection/refraction tomography, i.e., by imposing the constraint that the layer structure and the local velocities do not change outside the reservoir (and in the shallowest part) over time. We thus get coupled models that are physically consistent, with a better spatial coverage and higher information redundancy. The new method is illustrated by a marine case history from the North Sea.

Time-lapse refraction seismic tomography for the detection of ground ice degradation

“…Vesnaver et al, 2003;King, 2005), similar efforts to investigate the potential of a time-lapse refraction seismic tomography approach for the observation of shallow targets have not been reported so far.…”

Contribution of 3-D time-lapse ERT to the study of leachate recirculation in a landfill

“…During injection processes, if leachate content or gas migration creates resistivity variations, ERT using a time-lapse approach can be considered (i.e., repeating the ERT survey several times during the injection). Time-lapse ERT is used to study environmental processes because it focuses on electrical resistivity changes in the subsurface produced by groundwater flow (Vesnaver et al, 2003). The main potential applications are pollution plume monitoring (DeLima et al, 1995;Benson, 1995;Benson et al, 1997;Day-Lewis et al, 2003) and the location of shallow or deep infiltrations or recharge zones (Descloitres et al, 2008a,b).…”

Optimal experiment design for time-lapse traveltime tomography

“…Differential imaging approaches can be problematic in cases where the dominant changes in delay time are due to localized effects near the sources or receivers which are not the target of the monitoring experiment e.g. water table variations or seawater temperature changes (Vesnaver et al, 2003) in the case of timelapse surface reflection surveys. However, deep boreholes are relatively stable environments and semi-permanent arrays offer an almost ideal scenario where changes in formation coupling are minimized.…”

“…repeated reflection seismic surveys. Unfortunately, a host of logistical constraints hamper the repeatability of such surveys, such as difficulties in exactly replicating the source/receiver geometry, changes in overburden conditions (Vesnaver et al, 2003), and sufficiently matching the seismic processing flow (Ross and Altan, 1997).…”