The features of the geological structure of the Verkhnechonsky oil and gas condensate field and their influence on the field development and operation system

Abstract

The study aims to analyze the relationship between the redetermination of the complexity of the geological structure of the Verkhnechonsky oil and gas condensate field and the schedule adjustment of the field development plans. The paper uses the data on the exploration and production wells obtained from the pilot operation of JSC Verkhnechonskneftegaz, the geophysical work results, and the research materials publicly available in the press. The geological structure of the Verhnechonskoye oil and gas condensate field is unique in its complexity. This is due to the following factors: a combination of tectonic disturbances accompanied by the intrusion of traps; high mineralization of the reservoir water; sharp variability of the filtration and reservoir properties of the producing horizons by area and section due to the unevenness of the lithological composition of the reservoirs, their salinization and complete pinch-out. The development system of any field should take into account the peculiarities of the field’s tectonic and lithological-facies structure, and meet specific technical and economic requirements for drilling and operating wells. The complexity of the field structure requires a thorough selection of a development system that inevitably changes as the features of the field structure are studied, e.g. vertical drilling suggested at the initial stage of the filed development was shortly after replaced with inclined-horizontal drilling with the calculation of two options. Within the pilot operation project of the Verkhnechonsky field, JSC Verkhnechonskneftegaz has developed two variants of uniform grids of directional and horizontal wells with pattern flooding for the most explored deposits of the Verkhnechonsky horizon of blocks I and II. Because of the intensive processes of the reservoirs’ secondary salinization, the flooding method required a study of the reservoir water composition. However, the proposed drilling plan using a downhole engine and gamma-ray logging could not ensure the wellbores ducting through the most productive sections of the horizon, therefore, the flow rates of some directional and horizontal wells were not high enough. To increase the drilling efficiency, the specialists of the Drilling Department (JSC Verhnechonskneftegaz), together with the Department of Geology and Field Development (Schlumberger Ltd.), proposed a new methodology that increases the drilling efficiency by using a rotary-controlled system, logging-while-drilling, and geosteering. Thus, the development system of the Verkhnechonsky oils and gas condensate field was changing in the process of specifying the field’s geological structure, anisotropy reservoir properties, and the thickness of the producing horizons in size and cut, their salinization and pinch-out, and the composition of the reservoir waters.