Abstract

The types of features of electric analogue patterns of groundwater movement found most frequently associated with hydrocarbon accumulation are: regional systems, ascending limbs, and stagnant zones. The reason for the preferential accumulation of hydrocarbons under these hydraulic conditions appears to be an increase in the effectiveness of the structural and lithologic traps. This may be explained by: 1) the large quantities of hydrocarbons transported by the regional flow systems; 2) effective segregation of hydrocarbons from the transporting water owing to a divergence between the flow directions of the migrating fluids; 3) effective mechanical (capillary) filtration by the large number of permeability changes along ascending, hence cross-formational flow paths; 4) effective segregation of gases from the water due to a rapid decrease in pressure along ascending flow paths; 5) slight inclination of oil- or gas–water interfaces causing even minor structures to become relatively effective traps.Examples of theoretical subsurface hydrodynamics as well as of practical observations of hydrocarbon occurrences found in literature implicitly or explicitly corroborate these findings. 1) According to Kortsenshteyn 1964, the amounts of economic hydrocarbon reserves are directly proportional to the volume of the transporting flow system; 2) the consistent association of hydrocarbon accumulations with artesian basins often reported by Soviet petroleum geologists and hydrogeologists clearly indicates conditions favorable for hydrocarbon associations in regions of ascending groundwater flow; 3) by application of Hubbert's equation given for the tilt of the oil– or gas–water interface a theoretical ratio of 8.4:1 is expected for preferential association of hydrocarbons with zones of stagnant and ascending groundwater as compared with the lateral limbs of flow systems along the Etzikom Coulee cross section, and by analysis of the analogue flow-pattern an empirical ratio of 6.8:1 is found, representing a good agreement between anticipation and facts; 4) in the Volga–Ural petroleum province a definite decrease in number and importance of major hydrocarbon fields with decreasing depth is reported, suggesting an effective filtration as a consequence of the ascending movement of groundwater.Thus the theoretical considerations, experimental results, and practical observations all indicate that certain hydrocarbon accumulations are identifiably related to the presently prevailing pattern of groundwater flow. This, in turn, can be realistically approximated from the configuration of the water table and consists of topographically controlled, hydraulically continuous, and regionally unconfined flow systems, modified in detail by the local heterogeneities of the geologic framework.

You do not currently have access to this article.