Deep-seated regional reservoirs of the Lower Jurassic formations in the Yenisei-Khatanga and Eastern parts of the Gydan oil and gas bearing areas: structural models and formation settings

Areas having different composition within the Toarcian, Pliensbachian, and Hettangian-Sinemurian reservoirs and ranging from mainly sandy to argillaceous-silty, which are regularly distributed across the region, are delineated. Environments where permeable sequences and impermeables were accumulated mainly in marine conditions are discussed. A set of thickness and composition maps is for the first time created for the permeable sequences of regional reservoirs throughout the region under consideration. It is shown that all the Early Jurassic long, transportation of silt-and-sand material from the Siberian Platform was the most intensive. Therefore, composition of the Lower Jurassic deposits in the vicinity of this provenance area is more sandy than in the areas neighbouring with the Taimyr Orogen. Common features of regional reservoir quality variations depending on their depth of occurrence are discovered. Granular reservoirs occurring at the depth up to 3.5 km have the higher porosity and permeability. The reservoir porosity is reduced by 2-2,5 % with each next kilometre of depth. Starting from the depth of 4.5 km, the open porosity typically does not exceed 12-13 %; reservoirs occurring deeper than 5.5 km have open porosity close to their cutoff value. Reservoir permeability also decreases down the section. Prediction of thickness of underexplored reservoirs is carried out using the available limited analytical and production logging data, the revealed regularity of variation in their porosity and permeability depending on depth of occurrence, and analysis of permeable rock associations’ composition. The authors delineated the areas of reservoir local occurrence and absence. The former can be classified into the areas having the highest, medium, decreased, and low reservoir thickness. Quality of the Laidinsky, Kiterbyutsky, and Levinsky impermeable beds all over the study area; quality maps are build for each of them