My question relates to the potential damaging effect (lowering strength and stiffness properties) of thermal expansion on shale. Is this phonemenon important in a tempersture range from 0 to 40 °C and how it affects the mechanical behaviour of shale, clay rock and of that kind or can it be disregarded? Is there any research in the temperature range between 0 and 40°C?
I don't think this makes a big difference, if at all. A 40 degree temperature difference will result in minimal thermal expansion of both, the minerals and the pore water. So the porosity is not affected much. If you have swelling clays that change hydration states upon temperature change might be an issue.
Thermal expansion is rather important at really high temperatures during steam flooding of oil reservoirs etc.
It might be worth checking the work that has been done for radwaste repositories where the radioactive waste results in some heating of surrounding mudrocks (like for Boom Clay, Opalinus shale or Callovo-Oxfordian shale in BE, CH, F)
Dear Christian,
Regarding your query on the sensitivity of thermal expansion of shale between 0 and 40 degrees Celsius,
1. Depending on type of shale species, chemically-sensitive smectitic-shale will naturally have more sensitivity with that of a chemically-insensitive, naturally-fractured quartz-illite shale - on thermal expansion.
2. The thermal expansion of both the above shale species will remain sensitive under deep drilling resulting from geo-mechanical issues.
3. The thermal expansion of both the above shale species will remain sensitive around 40 degrees Celsius, as in that range, the thermal expansion is associated with the expansion of the rock shale, which in turn, may enhance the resultant effective stress of the respective shale reservoir.
4. In case of deep drilling, there will be a competition between this enhanced effective stress of shale as against the mitigated pore-fluid pressure in the vicinity’s of the bore-well, and thereby making a complex coupling between rock-expansion, pore-fluid expansion and thermal-expansion.
Regards
Suresh Kumar Govindarajan.
Suresh Kumar Govindarajan
Thank you for the answer. This helps me a lot.
In our research of rock thermal decompaction (induced by uneven and anisotropic mineral grains thermal expansion) the uniform rock heating with rate 2° / min up to 100 °C did not result in observable effects; the expansion conserved a reversible character. However, I believe that some effect of strength/stiffness loss might be observable at multi-cyclic uniform rock heating in this temperature interval (as well as at 0 – 40 °C). The presence of water (fluid surface-active to minerals) usually enhances the decompaction effect.
In general the high content of quartz (~ 35 - 40%) in shale makes this type of rock sensitive to thermal expansion effects because of relatively high and anisotropic thermal expansion of α – quartz.
Zaraisky G.P. and Balashov V.N., (1995), Thermal Decompaction of Rocks, Fluids in Crust: Equilibrium and Transport Properties, Ed. K.I.Shmulovich, B.W.D.Yardley, and G.A.Gonchar, 252 -- 284. Book Chapter.
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