Abnormally high formation pressures in jurassic-cretaceous reservoirs of Arctic regions of Western Siberia

Abstract

Results of the study of the structure of hydrodynamic fields in Arctic part of the West Siberian sedimentary basin have designated the main region-specific hydrodynamic feature consisting in the phenomenon of abnormally high formation pressures widely spread at depths of 2.8-6.0 km within Jurassic-Cretaceous reservoirs. The two types of natural pressurized water systems which have developed in the region are: 1) elision (geostatic and geodynamic) system most common in the interior regions, and 2) infiltration aquifer system inherent in the external, near edge zones. As the depth increases, two hydrodynamic zones are distinctly distinguished (from top downwards): hydrostatic and enhanced evolving into AHFD (abnormally high formation pressure). Most of the Aptian-Albian-Cenomanian aquifers belong to the first type. Hydrodynamic field stresses tend to increase in the lower lying Neocomian complex where the already elevated formation pressures gradually build up, to the extent of AHFP in the lower horizons. The Jurassic aquifer complexes in the central parts of the Yamal-Kara depression exhibit either enhanced or abnormally high formation pressures, which decline to hydrostatic levels towards the basin periphery. The anomaly coefficients of formation pressure reach the value of 2.2. The established piezo-minima zones extending along major petroleum charge zones, extending along the major hydrocarbon generation zones (Bolshaya Kheta and Kara megasyneclises) associated with the largest areas of petroleum accumulation (Vankor-Suzun, Bovanenkovo, Urengoy, etc.).