Upper Paleozoic reef systems of the Rubezhinsky Trough (southern part of the Buzuluk Depression)

Abstract

Background. The Rubezhinsky Trough has been remained one of the most poorly studied petroleum areas of the Orenburg region to date. At present, Gazprom Neft conducts systematic exploration work within the trough at five license areas of the South Orenburg Cluster. Aim. The purpose of this article is representation of preliminary new dates on a geological structure of paleozoic reef systems within the Rubezhinsky Trough. Materials and methods. The main original materials for the work are the results of the interpretation of the 3D seismic carried out at four license areas. In addition, results drilling and regional sedimentation models were involved for analysis. Results. Regional models of Upper Paleozoic reef systems of the Rubezhinsky Trough have been extensively detailed as a result of the interpretation of 3-D seismic data within the South Orenburg cluster. It was first established that isolated reefs were formed in the interval of the Ardatovian and Mullinian regional stages (Givetian Stage of Middle Devonian) of the research area. Ardatovian-mullinian isolated reefs are covered with clay deposits and represent potential lithological traps for petroleum deposits. Isolated reefs, isolated carbonate platforms and the southern margin of the vast South-Buzuluk carbonate platform with barrier reef systems have been identified for the Frasnian Stage. Isolated frasnian reefs are potential hydrocarbon traps. Barrier frasnian reefs together with increasing them early famennian ones form a series of structural hydrocarbon traps in the overlapping complexes. The significant progradation of the margin of the famennian carbonate platform towards the Pre-Caspian paleobasin is established. Famennian progradation complexes form several large clinoforms which are potentially forward looking for the search for structural-lithological petroleum traps. The barrier reef system has been confirmed for the evaporite-carbonate complex of the Okskian regional stage. Okskian reefs border the late visean epicratonic carbonate platform. Relatively large reefs of the carbonate platform barrier system were identified in the interval from Podolskian regional stage (Carboniferous) to Asselian Stage (Permian). This barrier system has progradational architectures towards the Pre-Caspian paleobasin that was formed from the end of the Middle Carboniferous to the end of the Artinskian Age of the Early Permian. Podolskian-asselian barrier buildings predefine the development of structural hydrocarbon traps of various sizes in overlapping Lower Permian deposits. Conclusions. A preliminary analysis of 3-D seismic data indicates the significant role of the paleozoic reef systems in the formation of the sedimentary complex of the Rubezhinsky trough.