Hidrológiai Közlöny 1942 (22. évfolyam)

Szakosztályi ügyek

472 János Dinda usually arranged in such a manner that at first the upper part of the oil-bearing zone is being opened up and the lower one, containing water also, remains shut or is shut off. In such an instance only crude will be produced but by the lapse of time when the supply of crude shall be exhausted, water as well begins to reach the surface and finally only water will be lifted. When this situation arises the cementing-off of the lower part of the producing horizon will for some time remedy but as time rolls on the well will again go to water. Should production progress at a high rate, water will cone and then the well shall prematurely begin producing water. Similar is the situation when the field being of the structural type, edge water or that originally in the basin reaches the hole drilled. The point where edge water comes to meet the oil is called „oil-water contact". Theoretically this contact is a level. However, actually this is not the case. In most instances the contact is most irregular as it has been found to resemble a belt instead of a plane. Therefore, the formation shall have a part, an upper one, containing crude alone, then, another comprising water and oil, and hereunder there will prevail a third one made up of water alone. The more uniform the formation and the less viscous the oil, the more .will the oil-water contact be resembling a plane. Should the formation be not uniform in character water in the less porous and less permeable parts will, due to capillary action, rise to a higher level than in those that are porous and permeable to a more substantial degre. As production shall progress, viscosity diminishes and thus the oil-water contact will become more and more complicated. Some writers advance the theory that foreign matters solved by the water originally in the basin exert a chemical action upon the oil, making it more viscous and consequently water will encroach with much more difficulty. In case of lenticular structure the oil-water contact might be different in each and every Ienticle. In several fields utmost care is being taken to ascertain the progress of edge water from year to year towards the axis of such particular field. Edge water might tend towards the axis for two reasons. Namely, one of them is that due to oil production a decrease in pressure sets in on the top of the dome, resp. structure. The other reason is the pressure exerted by the water, that is: the hydrostatic pressure. These two effects do in most instances prevail jointly. Hydrostatic pressure, however, can make itself felt in the upward encroachment of water only in the case the pressure in the upper part of the structure decreases due to oil and gas produced or released thence. The extent to which hydrostatic pressure can develop does depend in addition to the difference ensuing in pressure also from the porosity,