Isolated formation pressure zones with multi-layered seal regions and superimposed hydrocarbon systems

Nowadays, there is a fairly large number of examples of the development of so-called isolated areas of abnormally high formation pressure (AHFP). The condition for their formation is not only lateral but also vertical isolation, that is, a return to hydrostatic pressure beneath the AHFP zone and, consequently, the presence of a lower seal associated with gas generation processes and its entry into adjacent microporosity zones. Data on this part of the section are very limited due to both objective (geological) and subjective (technological) factors. Moreover, the AHFP interval is often perceived as «infinite» with no lower boundary. Similarly, the appearance of igneous (effusive) rocks in a section is often perceived as the base of a sedimentary cover, whereas a multi-kilometer «normal» sedimentary section can be established beneath the effusive rocks. The purpose of this article is to draw the attention of specialists to the possibility of such phenomena as the isolation of AHFP zones and their impact on hydrocarbon systems. Particular attention should be paid to the influence of isolated AHFP zones on the increased potential of underlying complexes, where new promising horizons may be identified. This is particularly relevant for deep and ultra-deep sections. Such pressure regressions must be taken into account when modeling the development of hydrocarbon systems, especially superimposed ones. Furthermore, isolation of AHFP can form vast areas with so-called «unconventional» massive reservoirs, which may become the target of exploration.

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