This paper describes a comprehensive analysis of the 3D seismic data, well logs, and cores from productive intervals of the Mayskoye and Festivalnoye fields. The analysis covered the sandstone layers of the lower part of Tyumen Formation and the fractured reservoirs of pre-Jurassic basement. The goal of this study was to build geological models that will serve as a basis for field development planning of the low-permeability, low-porosity reservoirs of the described intervals.
First, we completed a structural and tectonic analysis, i.e. identified the main mechanisms of structural and tectonic evolution. At the Festivalnoye field, the main anticline structure is a pop-up fold that was formed by displacements along a major regional-scale wrench fault. This conclusion guided the structural interpretation, and in particular, resulted in more reliable fault recognition and tracing. The fault tracing widely involved the Ant Tracking function. The revealed direction of a regional stress (interpreted from FMI and sonic scanner data) has enabled a planning of the optimal trajectories for horizontal wells that is of special importance when hydraulic fracturing is involved.
Second, we interpreted depositional environments and facies distribution of the Jurassic sandstone layers. In the Mayskoye productive interval we have identified two major parts of the section corresponding to different depositional systems: The lower section (zones J15—J16) was deposited in a braided river depositional system that fills the pre-Jursassic erosional relief. This environment was identified using the results of sedimentological core descriptions. The upper section (zones J12—J14) was deposited in a meandering river depositional system, with depositional cycles (sequences) topped with coals. This part of the section demonstrates higher heterogeneity compared to the lower unit deposited in braided rivers.
The results of facies analysis provided grounds for the selection of optimal algorithms for geological modeling and adequate honoring of the reservoir heterogeneity. The conclusion about facies and the evolution of fluvial sedimentation for the lower part of the Tyumen Formation is presented first time for the southeastern region of Western Siberia.