Interpretation and Practical Applications of Flow Phenomena in Clayey Media

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. The presence of clay in sandstone reservoirs complicates the interpretation of electric logs and can influence the flow properties of fluids. The water-clay interaction and, in particular, the double ionic layer concept has been applied to the study of macroscopic fluid flow phenomena from two points of view: [1] the mechanical driving of clay particles and [21 the ionic equilibrium which allows a generally reversible swelling of the clay to take place. In the latter case, an effective porosity has been defined in keeping with the fact that the swelling water in the double stratum does not participate in the flow, and the resulting permeability reduction has been calculated in function of the ionic concentration of the aqueous phase. Experimental proof of this theory is very effective in artificial formations. To study the practical problems raised by clayey sandstones, sandstones containing illite and kaolinite were examined with standard electrolytes [NaCl, CaCl2, KCl]. The permeability decreases conformed to the theory and depend on the nature of the clay, its distribution in the sandstone and the nature of the compensating ion in the clay. Clay particle driving occurred in both sandstones and artificial media, thus enabling the chances of plugging linked to salt-content variations to be evaluated. A study of this sort brings out the precautions that should be taken in drilling into clayey reservoirs and in making petrophysical studies. Introduction The presence of clay in natural porous media presents drilling and production engineers with various problems linked to the nature of clays and their reactivity.Interpreting electric logs with clay present is made more delicate when searching for oil-bearing zones.The interaction between clays and fluids in contact with each other [oil field water, mud filtrate injected water] is capable of modifying the capillary properties of the rock and, in some cases., can reduce the production capacity of wells by decreasing the permeability of the reservoir.