Geomodeling Concept For The Reservoir With High Heterogeneity

The “STC” oilfield was discovered in 1959., it is in production since 1960. and it is one of the most important oil field in Serbia. Up to 2017. on the field were drilled 87 wells.

Geological structure is represented by Sarmatian, Badenian and Jurassic formation. From the aspect of the current field development and quantity of the remaining balance reserves, the most important stratigraphic unit is Badenian which is made of terrigenous reservoirs of different composition and characteristics.

The main goal of this study is to identify the causes and control factors of the existence of different well production and water-cut reduction from Badenian. Badenian reservoir is characterized by high lithological heterogeneity and the rocks are composed from several lithofacies, such as limestone, sandstone and their variation. Each lithofacie has own petrophysical properties. Due to the frequent vertical and horizontal lithological heterogeneity, it was necessary to create a new geological model, including a detailed lithological characterization of badenian’s reservoirs and localize it.

In order to achieve this, it was necessary to include a detailed sedimentological and petrophysical interpretation of the badenia reservoirs, where all cores and well logs data were analyzed. The result of the interpretation is the separation of dominant lithofacies in the reservoir of Badenian. The next step was to define the diffusion of interesting litofacies, which required detailed analysis of seismic data and surface attributes analysis.

The result of all the above-mentioned modeling phases is a geological model that can help us in further development of the field, define the most prosperous zones for effective production wells allocation and necessary operations on existing wells. Also, oil reserves have been estimated for each of the facies, what will enable better field development and planning further production. The first positive results are seen in the overlapping of zones with a lower degree of water-cut in boreholes with increased content of sandstones, next to limestone, which leads to the conclusion that these zones have less water-cut of during the production. The research helped us to create search criteria for geological modeling of similar objects.