Possible seismic intensities had been mapped for the earth as a whole giving necessary analytical data for the structures that are planned, but will there be any effect on this predetermined seismic intensity of a particular zone where resources are extracted by deep drilling/mining process, although steps are taken to fill back to makeup the extractions.
I think large scale depletion of underground water/oil/minerals may create weak spot which may responsible for geological changes particularly during seismic activity.
Dear sir.
As a Geophysicist, I recommend the use of time-lapse 3D seismic data (called 4D) following your question.
The 4D seismic attributes allow us to analyze changes in reservoir status during production and of course, with the natural depletion of the reservoir.
The 4D seismic analysis technique consisting of seismic imaging, attributes extraction, and pattern recognition functions, coupled iteratively with high resolution, seismic forward and inverse modeling.
When I talk about attributes, it means both, the maps volume conventional amplitude analysis, and prestack analysis: AVO and seismic inversion. So, you use to examine similarities and differences among the seismic amplitudes your field. You need to think to start with a 3D baseline, and reference the next ones to it. This technique minimizes the difficulties in matching acquisition parameters, variable geometries, and technology improvements that have accompanied the development of 3D seismic methodologies over the years. The survey planning means that the ideal 4D monitor survey is an exact replica of the acquisition of the baseline survey. This involves repeating source and receiver positions and matching environmental conditions such as tide state and currents.
There are examples of seismic surveys that were first, in order to the preparation into a 4D dataset ready for inter-comparison, requires extraction of similar power spectra from the two / three / four seismic surveys. The inter-comparisons are accomplished in attribute-derivative space, since we have found that only the lowest frequency amplitude spectra preserve the best commonality among the differently acquired acoustic datasets. Specifically, the waveform envelope of the reflection strength is calculated and compared.
The normalization technique cannot correct for differences in reflection strength caused by orientation changes between the surveys relative to rock geometry in the subsurface, so the match is never perfect. Of course, you need another critical data: the well-logs from key-well (monitors) information to calibrate seismic changes observed during seismic monitoring at your field, leading to reservoir characterization that can predict pressure distributions, interface changes such as O/W contact movements, porosity anomalies, permeability boundaries, GOR changes, and in particular, bypassed hydrocarbons-all in true 3D and near real-time.
The prediction of changes in reservoir physical parameters such as pressure and fluid content from the 4D attributes and seismic analysis of changes in seismic amplitudes over time is ultimately an ill-posed, inverse problem. Consequently, forthcoming refinements to the 4D answer might be coupled to the results of forward models of the different physical types such as reservoir fluids, elastic, and acoustic properties.
Let me share this paper, I hope it is a very good synthesis of the applications of the 4D seismic techniques.
Best wishes,
Mario
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