Prediction of distribution of reservoir rocks of the Vendian Moshakovskaya suite within the southwest end of the Siberian platform

The lithological characteristic of the Vendian Moshakovskaya suite deposits of productive gas within the south end of the Siberian platform (the zone of the Angarskie plications and the Boguchano-Manzinskiy slope of the Prisayano-Eniseyskaya syneclise) was defi as a result of diffent-scale detailed lithological and petrophysical researches of core material and the analysis of well logging data.Type sections, the revealed regularity of their structure, the inversion of depositional conditions, lithological and petrophysical characteristics of Vendian reservoir rocks of the Moshakovskaya suite deposits and the prediction of their distribution are also presented in the article.The depositional sequence of ichnofacies in the Vendian deposits of the Moshakovskaya suite is described.
Materials and methods
Core material from 4 wells (the overall total is 700 m); 450 petrographic thin sections; the results of petrophysical researches (more than 350 porosity and permeability measurements); well logging data from 6 deep-hole wells, geological and field data; photographs of the full-length core from 6 wells and its lithological description. The complex of different-scale lithological researches included the researches of texture, structure, mineral composition of reservoir rocks, the structure of voids, using optical and scanning electron microscopy and the microprobe analysis.
Results
Productive gas deposits of the Moshakovskaya suite of the Taseevskaya depositional sequence is represented by a diverse set of variegated terrigenous, terrigenous-carbonate, sulfate and clay rocks.It is demonstrated, that the formation of the Moshakovskaya suite was originated under various facial conditions: alluvial delta complex, tidally-influenced flat land, shallow marine conditions.The distribution of reservoir rocks is determined by lithological and facies conditions of formation and direction of secondary changes, including fissility. Porous-fissured, mixed fractured-porous,and porous types of reservoir rocks are distinguished in different structural zones. Three main types of voids are distinguished in the porous type of reservoirs: intergranular, the voids of desalination of the carbonaceous cement, microvoids of the corrosion fragments of the potassium feldspar. The predominance of one type of voids or another in various structural zones is different.
Сonclusions
The maximum values of productivity are noted in the deposits with porous-fissured reservoir type, that is related to facies of bar bodies within the zone of the Angarskie plications.Thus, the facie zone of bar bodies is considered to be the most promising for searching zones of development of reservoir rocks in deposits of the Vendian Moshakovskaya suite.