Hidrológiai Közlöny 1942 (22. évfolyam)

Szakosztályi ügyek

470 János Dinda This water filming the sand grains is the so-called connate water, which is in fact fossil-bearing sea water. Accordingly, this connate water is in most cases salt, tho while no deffinite data to the effect are available, it might in principle be other than salt water. The formations are being made wet also by such water as will reach either by way of flowing or seepage down to them. This water in contrast to the one designated as connate water is called „meteoric", while practically it might be said to be rain water. There would certainly be some difficulty encountered in trying to ascertain whether the water on the sample taken from the deep is connate or one that had reached the sand grains from the surface. In general, the practice is to regard the water found adhering to the sand grains of the core as being connate. In spite of the fact that the connate water represents a substantial (10—20%) percentage of the pore volume and the accumulated water content of the sand is much more in excess of this (being 40—50%) often still pure crude leaves the formation as the water adhering to the formation is being retained by the adhesive force and the capillary action. It can easily be imagined that in the course of production some of this connate water under adhesion manages to get free and so reaches the surface together with the oil. This should explain the fact experienced with some producing wells that from time to time a negligible quantity of water reaches the surface altho the part of the producing formation is still quite distant from the oil-water contact. A. W. McCoy advanced a very interesting theory by stating that at all times oil tends to flow towards the relatively coarser-grained parts, and water, on the other hand towards, the relatively finer-grained ones, because the surface tension of water is double, nay, even twoand-a-half-fold of that of the oil, hence it gravitates towards the smaller capillaries. This theory has in practice been found to hold in several instances hence its being dealt with in trade papers. Thus, for instance, in Pennsylvania oil has been encountered so to say exclusively in coarser-grained streaks imbedded between finer-grained sandstones, and, in coarser-grained formations, in some cases also under such circumstances that the lower and upper finer-grained formation layers forming organic unit with oil-bearing coarser-grained formation were saturated with water. As has been explained above, oil entered the formation together with water. Such formation can be at times sand as well, tho by supposition it is more often clay or shale. This being the case oil is blended with water to such an extent that here can be no question of producing any oil and until it will reach such a state as will render