Cycles During Sedimentation in Bobrikov Interval, and their Influence on the Formation of Productive Reservoirs of Garshinskoye Field, Orenburg Region

This work aims to study the peculiarities of the formation of clastic sediments in the Bobrikov horizon of Garshinskoye Field, Orenburg Region. The work objective is to recreate the sedimentation conditions and to study the facies in order to support differently leveled OWCs in the Bobrikov horizon of Garshinskoye Field, sharp water breakthrough, and reservoir pressure drop during operation of a number of wells. The detailed correlation of Bobrikov sediments within Garshinskoye Field resulted in interpretation of three cycles of sedimentation (B2-2, B2, B2-1 reservoirs), characterized by different sea-levels and different dynamics of flows which carry mineral material from sediment migration area. Different levels of OWCs observed in B2-1 and B2 reservoirs suggest their hydrodynamic isolation. Commingled operation of deposits in different reservoirs results in sudden water breakthrough in the wells which penetrated a pure-oil zone in one reservoir and a water-oil zone in a different reservoir. The sharp drop in reservoir pressure in the wells of commingled operation is due to the fact that the design of the reservoir pressure maintenance system does not take into account a multi-reservoir structure of Bobrikov sediments, and injection wells are mainly targeted to the upper B2-1 reservoir with poorer rock properties in comparison to B2 reservoir