Regularities of the secondary processes in terrigenous deposits of the Nepa formation within the Chona group of deposits

Abstract

Introduction. For the first time, a comprehensive program for the study of terrigenous formations of the Nepa formation was implemented on the core of new wells of the Ignalinsky, Tympuchikansky, Vakunaysky sites and wells drilled before 2000 in these and adjacent areas. Secondary processes developing in the terrigenous deposits of the Nepa formation are identified and characterized, their stages are determined, the relationship with the sedimentation medium and tectogenesis processes is established, and the prerequisites for the areal forecast of zones of secondary rock change and zones of absence of such changes are described.
Aim. Identification of the patterns of the spread of secondary processes in the deposits of the Nepa formation, the degree of their influence on the properties of rocks. Determining the directions of forecasting promising areas of reservoir development.
Materials and methods. To create a detailed model of secondary changes, a core study of 17 wells drilled by Gazpromneft-GEO LLC and 46 wells drilled before the 2000s was conducted.
Results. The scheme of stages of post-sedimentation processes is proposed, taking into account the influence of sedimentation conditions, background immersion of the sedimentary basin and inversion-tectonic restructuring, accompanied by changes in water-fluid regimes; formation of tectonic disturbances, fracture zones; thermal effects of magmatic bodies.
Conclusion. Analysis of core material, Well logs data and well operation results shows that halitization, anhydritization, dolomitization and bituminization have the greatest impact on reservoir properties of the deposit. The remaining processes are developed locally at individual sites and their impact on the amount of reserves, as well as the porosity and permeability, is significantly lower. The restoration of the sedimentation history of sediments, their compaction, and tectonic movements of the territory makes it possible to predict the prospects of sites at the zonal and local levels.