Mapping the internal structures of fault zones of the sedimentary cover: a tectonophysical approach applied to interpret TDEM data (Kovykta gas condensate field)

Abstract

The article presents the results of studying the internal structures of platform fault zones with the use of a new tectonophysical approach to processing and interpretation of electrical exploration data obtained by the transient elec‐ tromagnetic method in the near field zone (TEM). In the study of the central part of the Kovykta gas condensate field (East Siberia, Russia), we applied the ideas of tectonophysics envisaging three stages of fault formation, which determine the three‐membered transverse zoning of a fully formed fault zone. Each subzone is characterized by a certain level of rock disturbance and corresponding electrical conductivity. Based on the analysis of electrical conductivity values, the boundaries can be determined between locations differing by the degrees of rock disturbance of the sedimentary stra‐ tum. Using a map of this parameter, it becomes possible to generally establish the boundaries of fault zones and specify internal subzones. The new approach was applied to assess the electrical conductivity of the reservoirs of the Kovykta field. It is established that there are several zones of faulting in the sedimentary stratum, which have not reached a final stage of development when a single fault plane is formed. Currently, these are zones of increased fracturing and dense occurrence of second‐order ruptures that are typical of platform settings due to their relatively weak tectonic activity. The zones are structurally non‐uniform, as evidenced by rheological layering of the sedimentary cover in the vertical cross‐section. A 3D electrical conductivity model of the largest fault zone in the study area shows alternating segments with more or less developed internal structures. Such segments are confined to layers that differ with respect to frac‐ turing. Exploration and development of hydrocarbon deposits can benefit from 3D modeling of large fault zones with the use of the tectonophysical approach for processing and interpretation of the TEM data. The models can provide addition‐ al arguments for improved decision making about locations for trouble‐free well drilling, as well as for selecting more effective methods for drilling sedimentary strata composed of complex horizontal layers.

Keywords

• fault zone
• sedimentary cover
• transient electromagnetic method (tem)
• tectonophysics
• kovykta gas condensate field