![overburden stress techlog overburden stress techlog](https://library.seg.org/cms/10.1190/INT-2017-0193.1/asset/images/medium/figure17.gif)
Initially, a calibrated rock-physics model was derived to provide a set of relationships between the elastic and petrophysical properties. In this study, the Biot’s coefficient from well-log data was calculated. This paper presents a comprehensive petrophysical and geomechanical evaluation of the unconventional reservoirs of lower Paleozoic age formation: lower Silurian and Ordovician deposits located in the onshore part of the Baltic Basin (Poland). Although, this parameter is necessary to determine the magnitude of the effective stresses acting in the reservoir, it is not included in the standard protocols used in Poland.
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Mineralogy plays an important role in controlling shale’s mechanical properties, among which one of the most problematic parameters to establish is the Biot’s coefficient. In upcoming discussions, we will tie the pore pressure and oveburden stress concepts together to determine the effective stress on rocks in the suburface.The complexity of shale formation interpretation requires an accurate evaluation of a detailed petrophysical model in association with the analysis of the geomechanical properties. So a general rule of thumb is the following:Īssume a rock column load of 1.0 if you lack information This is good ballpark number if you want to quickly do a hand calculation or do not have the data to calculate an average bulk density value.
Overburden stress techlog how to#
You can definitely read up more about how to account for this, but a lot of times it’s easier to assume a value of 1.0 as the pressure gradient for the rock column. the deeper you go, porosity tends to decrease because the rock is compressed more due to supporting more material above it. In real world applications, the bulk density varies with depth because the porosity changes with depth.
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Where the densitys have units of and the overburden stress ends up with units of. In oilfield units the overburden stress can be determined by the following expression with the simplifying assumptions: A lot of times, petroleum engineers assume average density values for the fluid column density and the bulk density. The second term on the right hand side of equation ( 1) represents the pressure caused by the rock column. The first term on the right hand side of equation ( 1) represents the pressure caused by the water column. = the bulk density as a function of depth = density of the fluid column as a function of depth You can account for both of these by using bulk density.īecause the overburden stress is the sum of all the material above a reference point, the mathematical expression to calculate the overburden stress is represented by the following expression: The sponge material are the grains, and the voids in the sponge are filled with water. If your still having trouble with the bulk density concept, think of the rock in the subsurface like a wet sponge.
![overburden stress techlog overburden stress techlog](https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs13202-021-01255-6/MediaObjects/13202_2021_1255_Fig11_HTML.png)
It is important to note that we use bulk density when calculating the pressure caused by the rock column, NOT the grain density. From the figure above, it is clear that the overburden stress at a depth, the datum point, is the sum of the pressure caused by the fluid column and the pressure caused by the rock (fluid-grain mixture).