Regional hydraulic behavior of structural zones and sedimentological heterogeneities in an overpressured sedimentary basin

• Definition of the hydraulic function of fault zones and regional aquitards.
• Identification of fluid-potential minimum zones, i.e. hydraulic hydrocarbon traps.
• Determination of diagnostic relationships related to the overpressure dissipation.
• Generalization of overpressure patterns and basic types of p(z) profiles.
• Methodological development for early phase reservoir prognosis.

The paper presents the results of a regional scale hydrogeological study conducted in two areas of the Pannonian Basin in Eastern and Southeastern Hungary. The purpose of the study was to investigate the role of fault zones and sedimentological heterogeneities in areas of overpressure dissipation and hydrocarbon entrapment. The Study Areas (∼10,400 km2 in total) were chosen so as to see the effects of their differing geological characteristics, specifically that of a regional scale Pre-Neogene basement high (Battonya High), and two regional scale depressions (Derecske Trough, Békés Basin). Groundwater flow patterns were inferred for both areas from distributions of fluid dynamic parameters presented on potentiometric surface maps, vertical hydraulic cross sections and pressure-vs.-elevation [p(z)] profiles. The data suggest that both fluid-flow patterns and the potential for hydrocarbon entrapment are predominantly controlled by the dissipation paths of overpressure. In turn, the routes of overpressure dissipation are controlled by the structural and sedimentological heterogeneities of the aquitards. Diagnostic relationships were found between the heterogeneities and fluid-potential anomalies, as well as hydrocarbon occurrences. The observed pattern of overpressure dissipation has allowed the identification of seven regions by seven basic types of pressure–elevation profiles, p(z). As well, a new concept, “the upper boundary of hydrocarbon migration” was proposed. Finally, based on the established diagnostic relationships and the deduced type-profiles of pressure–elevation, a hydrogeological methodology was developed which could be used in other areas and for other purposes, e.g., exploration for groundwater and geothermal resources, petroleum and in preparation for numerical modeling.