LAND SUBSIDENCE
Whether capturing the minute variations in earth’s surface using continuous Global Positioning System; or, Extensometers; or, Interferometric Synthetic Aperture Radar would justify the spatio-temporal extent of land subsidence resulting from "petroleum" ‘reservoir compaction’?
In case, if we have a rise in groundwater table; or a groundwater recharge that directly leads to ‘soil swelling’ or an ‘uplift’ respectively (right above the petroleum wellsite), won’t the resulting soil behavior in the unsaturated zone lead to a significant subsidence at the surface level?
If so, then, how could we correlate such a land subsidence to be associated with (petroleum) reservoir compaction in the absence of a proper hydrogeological investigation?
Since, there is no actual reduction in piezometric level within the confined reservoir (pay-zone) thickness, whether, is it becoming too difficult to effectively analyze the mechanism of land subsidence associated with a petroleum reservoir (even, if we manage to deduce the data on the changes in reservoir thickness as well as compressibility)?
In case of a petroleum reservoir, whether the distribution of stress at the interface of a seal and the reservoir would follow the simple correlation, where the ‘total vertical stress’ remains equal to the summation of ‘reservoir pore pressure’ and the ‘effective stress’?
How do we ensure whether Terzhagi’s one dimensional consolidation theory (in the vertical direction) would remain highly sufficient; or, should we also consider the Biot’s coefficient taking into account the load transfer (or maximum and minimum horizontal stresses) on the lateral horizontal directions in deducing the changes in reservoir thickness?
Do we have a direct mechanism by which the data on (petroleum) reservoir compaction that would directly get translated into its equivalent land subsidence in the absence of directly measuring the changes in earth’s surface and reporting the land subsidence using InSAR?
Dear friend Suresh Kumar Govindarajan
The relationship between petroleum reservoir compaction and land subsidence is complex and indirect. While it is true that subsidence can be a result of reservoir compaction, there are many other factors that can contribute to land subsidence, such as soil properties, groundwater, and tectonic activity.
Measuring the minute variations in the earth's surface using continuous GPS, extensometers, or InSAR can help to detect and monitor land subsidence over time, but these methods cannot provide direct evidence of the cause of the subsidence. A proper hydrogeological investigation would be necessary to determine whether subsidence is due to petroleum reservoir compaction or some other factor.
In the case of a rise in groundwater table or groundwater recharge, it is possible for the resulting soil behavior in the unsaturated zone to lead to significant subsidence at the surface level. However, this subsidence may not necessarily be associated with petroleum reservoir compaction.
The distribution of stress at the interface of a seal and the reservoir in a petroleum reservoir can follow a simple correlation where the total vertical stress remains equal to the summation of reservoir pore pressure and the effective stress. However, the relationship between reservoir compaction and land subsidence is not a simple one-dimensional consolidation process. Biot's coefficient may need to be considered to take into account the load transfer on the lateral horizontal directions in deducing the changes in reservoir thickness.
Therefore, it is difficult to directly translate data on petroleum reservoir compaction into land subsidence without a proper investigation of the geological and hydrogeological factors involved.
I don't know if this is helpful because it pertains to groundwater but it might lead you somewhere useful. There is a long is history of major subsidence in the Houston area that might have led to published academic research. https://uh.edu/news-events/stories/2022-news-articles/october-2022/10112022-houston-subsidence.php
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