Effect Of Underground Waters In Localizing Oil Accumulations

Abstract

Oil and gas are fluids but our prospecting methods have been based mainly on observations of the reservoir rocks. Little use has been made of measurements of the physical and chemical properties of their fluid contents. There is now general agreement that petroleum originates in a very disperse state and is segregated into oil pools during the compaction and lithification of the sediments. The mechanism of this process is little understood, but it may be caused by the expulsion of pore water from the sediments and involve a capillary filtering action. If the routes of water migration and the location of capillary filters could be predicted, much more use could be made of our available geological data in predicting likely places for oil to accumulate. Usually the oil remains where it was originally trapped. Sometimes, however, the regional dip may be reversed and the oil will then run to the other end of the aquifer that contains it. In mountainous areas, reservoirs are severely disturbed and often breached so the oil can run out, which is the principal cause of surface oil seeps. In such areas an effort should be made to locate the sites of the original accumulations, and then consider where the oil might now be.

Tilted original oil/water contact in the Arab-D reservoir, Ghawar field, Saudi Arabia

“…• As discussed above, the possibility of fluid flow along the flanks of the Ghawar field is inconsistent with the field's initial pressure data, the lack of aquifer support during production, and the conclusions reached by Dickey (1963) and Chiarelli (1973) concerning stagnant aquifers.…”

“…This leads to the possibility of fresh water introduced from shallower aquifers as 'floating' on top of the more saline water. Dickey (1963) formulated similar ideas when discussing the general topic of underground waters and oil exploration. He later repeated the idea that a tilted OOWC does not necessarily imply hydrodynamics, especially in basins where the aquifer salinity shows high contents of chlorides, calcium, and total dissolved solids that indicated stagnant aquifers (Dickey, 1968(Dickey, , 1988.…”

“…Where hydrocarbons are trapped deeper in the sedimentary basin, the flow in the aquifer leg may lead to the dynamic tilting of the OOWC. Dickey (1963), Dickey and Soto (1974) linked aquifer activity with chemical composition at the scale of the sedimentary basin, and showed that highly saline brines are characteristic of static aquifers. Of special importance for this paper was the concept introduced by Bond (1973Bond ( , 1975 of aquifers in static equilibrium even though changes in hydraulic head were measured.…”