The paper discusses the approach to the study of sediments related to the development of organic buildups in the Syrachoy formation of R. Trebs and A. Titov oil fields. Characterization of the depositional environments in which the Upper Devonian carbonate sediments were accumulated within the license area comprising these two fields presents a challenging task due to the geological complexity of this reservoir. This complexity is caused by high facies heterogeneity of the deposits, the influence of secondary diagenetic changes and the geometry of the void space. It is well established in the industry that the prediction of storage and flow properties for such reservoirs is possible only by means of their integrated studies and comprehensive analysis of all the available G&G and production data including core, well logs and seismic.
The first step to understanding the geology of the study area was the identification of the sedimentary conditions, i.e. the primary initial factors that predetermine the geometry of the void space, its complexity and trends in its spatial distribution and at the same time control all further stages of the reservoir formation. Lithological typification of the section coupled with the well log interpretation and seismic data helped to establish the main depositional trends. The findings were used to identify three facies zones, i.e. back reef, the reef crest (build-up itself) and fore reef. The results of core studies on conventional plugs and whole-core samples provided evidence on the prevailing types of the reservoir rock proved in the survey area: fine vuggy, fractured-vuggy-porous, fractured-vuggy and fractured-porous. The depositional model calibrated against the established geological heterogeneity may be used to predict spatial changes in reservoir properties and determine the most promising zones.
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