Distribution characteristics of abnormal formation pressures in the aquatic area of the Sakhalin shelf

Introduction. The conditions determining the distribution of abnormal formation pressures in the aquatic area of the Sakhalin shelf are analysed using boring data.Aim. To analyse the genesis of abnormally high pore pressure (AHPP) or abnormally high formation pressure (AHFP) zones and identify the pore pressure heterogeneities of the Sakhalin shelf.Materials and methods. Data systematization and statistical generalization, partial borrowing of materials from field data, reference literature and published materials. Modelling of the AHPP (AHFP) formation process was performed using the PetroMod software (Schlumberger).Results. The study revealed the isolated AHPP zones of the Sakhalin shelf, related to the syngenetic AHPPs and typically encountered in facies that develop downward the regional dip and consist of deltaic sediments, formed subsequently in the environments of internal neritic (subsaline-aqueous and offshore-marine sediments) and middle neritic (shallow marine sediments) zones, i.e., in places with the large mass accumulation rate. From this position, the AHPPs (AHFPs) in the Paleo-Amur deltaic sediments of the Sakhalin shelf were studied. Various procedures and direct borehole measurements proved the sectional presence of AHPP (AHFP) zones. Within the limits of the Sakhalin shelf, an increase in the formation pressure is recorded in several boreholes, i.e., zones of abnormally high formation pressure (AHFP) are revealed. The process of forming AHPP (AHFP) should be modelled based on the knowledge about the compaction processes of rocks, as well as their initial, final and normal porosity, density and pressure.