Dear Mr. Lakkundi,

the primary mineral assemblage of the rocks changes with age, particularly as far as the clay minerals are concerned. At the very end crystalline rocks only contain biotite, phlogobite, paragonite or even the rocks are devoid of clay minerals under very dry metmoprhic conditions. Kaolinite-group minerals occur only up to the low-grade stage of metamoprhic conditions and smectite and some other swelling chlorites appear even later and pesent at very low grade conditions. In that way age and diagenesis/metamorphism run along with each other and so do the clay mineralogical parameters. On the other hand also the textural and structural parameters , in other words micro porosity and permeability are subjected to alteration as it is the composition of the intrastratal solutions which change along with the afore-mentioned conditions. All of these effects have implications on the resistivity. This has also consequences on the IP when the grain shape and and orientation is concerned or OM changes from coal through anthrazite, semigraphite into to well-crystallized graphite. The later may also have been derived from metamorphosed hydrocarbons such as epit- to kataimpsonite.

The mineral and organic matter is subjected to an alteration with depth, age and the P/T regimes and so do the electrolytic parts of the pore solution.

Kind regards

H.G.Dill

Because in each geological period a number of climatic conditions prevailed

Well,

related to variation of groundwater quality(TDS), and water saturation, also to the differentiation in minerals percent from place to place.

Regards

Dear Mr. Lakkundi,

the primary mineral assemblage of the rocks changes with age, particularly as far as the clay minerals are concerned. At the very end crystalline rocks only contain biotite, phlogobite, paragonite or even the rocks are devoid of clay minerals under very dry metmoprhic conditions. Kaolinite-group minerals occur only up to the low-grade stage of metamoprhic conditions and smectite and some other swelling chlorites appear even later and pesent at very low grade conditions. In that way age and diagenesis/metamorphism run along with each other and so do the clay mineralogical parameters. On the other hand also the textural and structural parameters , in other words micro porosity and permeability are subjected to alteration as it is the composition of the intrastratal solutions which change along with the afore-mentioned conditions. All of these effects have implications on the resistivity. This has also consequences on the IP when the grain shape and and orientation is concerned or OM changes from coal through anthrazite, semigraphite into to well-crystallized graphite. The later may also have been derived from metamorphosed hydrocarbons such as epit- to kataimpsonite.

The mineral and organic matter is subjected to an alteration with depth, age and the P/T regimes and so do the electrolytic parts of the pore solution.

Kind regards

H.G.Dill

Excellent answer by Dr. Dill. Essentially the resistivity of a rock formation depends on the mineralogical composition, water saturation, porosity & permeability, compaction, weathering, etc. Nothing to do with the age. However if one observes such differences, then the rock samples have to be examined with respect to the physical, chemical, mineralogical, petrological and hydrological parameters.

The main factor for this the increment in range and resistivity value due to the natural load in rock/overburden material load or we can say also natural compaction.

Resistivty of rocks depends on the property of the rock and fluids thats contain there may be a rock of the same type but with different property and fluid contain therefore give different readings of resistivty, either increased resistivty with depth may be attributed to increasing compaction of rock and decreasing porosity and thats led to increase its resistivties.

Escalating in resistivity of rocks has nothing to do with age, but to the changes happen to minerals of the rock and so contained liquids

Resistivity of a rock solely depends on the mineral composition, porosity, water content and permeability. However, the same type of rocks with different ages can have different resistivity, due to the modification of the parameters mentioned. For e.g: Lets assume both rocks have same porosity, permeability and water content (considering different age) but still can have different resisitivity due to the change in mineral composition with age. The mineralogical change is attributed by weathering over the period of time.