Changes in formation fluid composition during development of multi-layer fields with faults

The purpose of this work is to identify the interaction between the developed and undeveloped oil deposits in a multi-layer field, complicated by the fault causing hydrodynamic connection between the layers. The study is carried out through flow simulations for a hypothetical sector of a multi-layer oil field. The multivariate calculations carried out made it possible to conclude that the presence of a hydrodynamic connection through the fault between the developed deposit and the deposit left for later production can significantly influence production dynamics, and lead to changes in reserves, composition and properties of reservoir oil in the undeveloped deposit before putting it into production.
Materials and methods
The study was performed on the basis of literature analysis and numerical simulation using a compositional 3D model of a hypothetical multi-layer oil deposit with parameters corresponding to one of the fields in Western Siberia. The model is implemented in the RFD tNavigator simulation software.
Results
The research carried out has shown that the presence of hydrodynamic connection through the fault between the developed deposit and the deposit left for later production can manifest itself in: • partial maintenance of reservoir pressure in the developed reservoir due to the fl infl w along the fault from the undeveloped reservoir, with a positive eff on the well performance, mainly in the near-fault areas; • changes in the reserves (and original oilin-place), composition and properties of the reservoir oil of the undeveloped deposit before putting it into production; • non-monotonic behavior of the dynamics of the production gas-oil ration and bidirectional changes in oil saturation in the zones of secondary gas cap formation, which are aff ed by the infl w of fl s along the fault. At the same time the specifi results of the hydrodynamic connection of the deposits along the fault essentially depend on the reservoir properties of the corresponding layers. The presented simulation results refer to the depletion drive with transition to the solution-gas drive. This situation is typical, especially in the initial period of development, for multi-layer deposits, where the need for simultaneous drilling on several reservoirs or transfer of wells between them often leads to decreased number of injection wells to maintain reservoir pressure. Nevertheless, the possible manifestation of other features of reservoir interaction during waterfl g is of interest for further research.
Conclusions
The presence of faults and near-fault decompaction zones, as well as the multilayer nature of the oil fi d, are usually considered as complicating factors for technologically effi ient and cost-eff e development. At the same time, adequate consideration of the possible impact of faults on the development of a multi-layered fi d during project design and monitoring allows to identify and take into account both negative and positive factors of such infl e. In conclusion, the authors would like to emphasize once again the importance of constant monitoring and assessment of the diversifi infl e of faults on the fi d development not only by geological data, but also by the analysis and monitoring of the fi d production.