Analysis of the Fault-Block Structure and Stress State of the Sedimentary Cover in Gas-Condensate Deposits: Basics of the Tectonophysical Approach

Abstract

Consideration is being given to the tectonophysical approach to the reconstruction of structure formation mechanisms and stress-strain state of rocks in hydrocarbon deposits localized in the platform cover, which has a complex structure in terms of rheological layering and disturbance by different-rank fractures. With the Kovykta gas condensate field, largest in Eastern Siberia, there were shown the main methods and ways of using modern achievements in tectonophysics for interpreting geological and geophysical information on the upper and lower parts of the sedimentary cover, unique in terms of volume and significance, that was obtained during geological exploration therein. Regularities of changes in the stress-strain state of rocks, found during the research, are combined into a tectonophysical model, which can be used as a base for other hydrocarbon deposits. The model is based on the concept of a zone-block structure of the platform cover, which is formed by a network of subvertical and subhorizontal fault zones that divide it into less faulted blocks. Disjunctive structures are highly fractured zones with concentration of relatively small low-amplitude faults, i.e. represent the early stages of faulting. The zone-block structure is formed mainly by tectonic or gravitational forces; in the first case, the stages and fracture characteristics are transformed onto the platform from the surrounding mobile belts, and in the second case they are determined by the presence of ductile rocks in the section capable of gravitational sliding. The graphic component of the tectonophysical model is 3D datasets that show the zone-block structure and stress state of rocks for the deposit with the degree of detail provided by key geophysical materials and, primarily, by seismic data. By modern GIS, this information can be quickly retrieved for any-size area of the studied rock mass and then used as a basis for solving production issues related to the development of deposits in fracture-pore reservoirs, or for analyzing general problems of their formation and dynamics.