Hello,
I know that there is a squeezing technique to sample pore water of mudrocks. But this technique is very sophisticated and potentially time consuming. My question if it is possible to evaluate the pore water chemistry of mudrocks from a chemical analysis of water sampled from boreholes?
The water samples would be from a depth of about 20-25 m. Is it possible to assume that the groundwater is in equilibrium with the pore water inside the hydraulic active pores of the mudrock and that the groundwater is representative for the composition of the pore water?
Unfortunately I can't rule out that there is a hydraulic connectivity to a quartenary aquifer.
Best Regards
It is good to try bore hole logger technique. Loggers are available to monitor the EC, TDS, pH , temperature and other water quality parameters in different depth internal Technique is quick and economical for pore pressure studies.
Dear Mr. Saxena,
thank you for your answer. But my main interest is the chemical composition of the pore water. There are correlations and possibilities to model the composition from the measurements you mentioned but I try to find out the real composition of the pore water chemistry by direct procedures.
Best Regards
Christian Günther
One difficulty you can expect to encounter is that at such shallow depths small conductive fractures enhancing vertical permeability that introduce fluids from outside of the aquiclude may dominate water quality not representative of the aquiclude. Large differences in hydraulic conductivity among thin sand/silt layers may also dominate the water contribution to the well. So much depends on the length of the screened interval when collecting bulk water samples. In a domestic water well (as opposed to a monitor well) open hole and gravel pack completions will not allow you to get a representative composition from low conductivity rocks. You can try repeated sampling to evaluate the effect of fluid mixtures occurring in the well bore. But, to recognize contributions from mudrocks will require extended analysis beyond the major ions to include trace metals and dissolved noble gas isotopes helpful for addressing residence times.
Dear Gunter,
According to Gorody explanation it may be helpful for your research to sample water borehole in rain period and also in dry one. The water sampled in dry period could be closer to rock pore water than rain period water samples. Also the knowledge of hidrogeology of area (recharge zones, springs, aquifers behaviours, ect) and chemistry of rocks involved could help you in order to determine the different ion apportations to waters sampled. It is good to sample all the boreholes, springs and rivers surrounding your study area having in count water flow directions and hidraulic connections, etc.
Hope this could be heplful
Have a nice day
DG
Предлагаю частный случай решения задачи: когда водоносный горизонт - коллектор граничит с прилегающим малопроницаемым слоем, который является источником поровой воды. Необходимо вскрыть только второй слой, а первый слой в скважине необходимо изолировать. Несколько раз извлечь воду из этой скважины. И вы получите ту воду, которая поступает из малопроницаемого слоя в эксплуатационный горизонт. Имейте в виду, если Вы выдавите всю воду из малопроницаемого горизонта, то она будет несколько другого состава.
Всего наилучшего
There are other techniques involving pumping with nitrogen. This requires you to seal the sample longitudinally, I believe this should be along the general flow direction. there wll be sealed in parts of the pore volume but you get the effective pore volume. Pumping nitrogen in one side and collecting water or everything, then remember to account for N2 and the pore volume it displaced. Nitrogen is small enough to displace pretty much everything, and can be modeled using something akin to the Buckley -Leverett Solution. This will destroy your sample in a way, since it's difficult to displace the nitrogen. Vacuum techniques are one way to get close to removing it.
Other considerations are anisotropic conditions, although shallow sample wells will allow you to characterize that. A Petroleum Engineering professor, Dr Jafarpour at USC is working on characterizing subsurface conditions with limited data, but I've not worked with him so I don't know it well.
If you only wish to chemically characterize your pore water then displace it with other water and model the diffusing effects. This is relatively simple to model, using the error function, to determine the mixing of your components and your input water.
- Badges
- Science topic
- Similar topics
- Geoscience
- Cartography
- Mapping