Experimental investigations concerning the compatibility of certain brines and rocks

Author: R. Skawiński

In sedimentary rocks with a porous structure which is filled by water or water based solutions there exists a physico-chemical equilibrium state in regard of a system composed of water solutions and minerals (mainly clay minerals) which constitute active rock components.

The equilibrium is represented by the stability of the amount of water sorbed by the rock components, i.e. the stability of internal rock swelling.

Any variation of the composition of the solution contained in the pore system creates an instability of the equilibrium state and results in the swelling or shrinkage of the rock mass.

Such internal swelling or shrinkage of the rock is characterised by a variation of the pore dimensions and it may be observed as a variation of the permeability during the flow of fluid in the rock-mass.

The paper presents the results of experimental investigations of the permeability variations in the rock implied by the replacement of liquids contained in the rock pore system by other liquids.

It was recorded that the replacement of the "native" brine filling the rock pores by brines of different composition may result in the variation of rock permeability of as much as two orders of magnitude.

An attempt has been made to explain the recorded results from the standpoint of the physico-chemical interaction in the brine-rock system.