Improved Integrated Approach in Reservoir Modeling by the Example of the Astokh Field

This paper summarizes the results of 3 years collaborative efforts of the Geophysicist, Production Geologist and Reservoir Engineers from the Astokh Development Team and the Geochemist from the LNG plant laboratory on integration of reservoir surveillance and reservoir modelling. In period 2015 - 2018 a large bulk of geological and field development data was collected in the Astokh field, in particular: cased and open hole logs, core, open hole pressure measurements, flowing and closed-in bottom hole pressures, well tests, new 4D seismic surveys (2015, 2018), fluid samples. Since 2016, essential progress was made in oil fingerprinting for oil production allocation. Simultaneously, the need for update of static and dynamic models was matured upon gaining experience in dynamic model history matching to field operational data (rates, pressures, results of well interventions). In other words, the need in update of geological architecture of the Astokh reservoir model was matured upon reaching critical mass of new data and experience. To revise well correlation, it was decided to combine different sorts of data, e.g. seismic, well logs and core data, reservoir pressures and oil fingerprinting. Different pressure regimes were identified for 3 layers within XXI reservoir. Pressure transient surveys were used for identification of geological boundaries where it's possible and this data was also incorporated into the model. Oil fingerprinting data was used for identification of different layers and compartments. Integration of pressure and oil geochemistry data allowed to identify inter-reservoir cross-flows caused by pressure differential. Based on all collected data, depositional model and reservoir correlation were updated based on sequential stratigraphy principles. As a result, a new static model of the main Astokh reservoirs was built, incorporating clinoform architecture for layers XXI-1’ and XXI-2. To check a new concept of geological architecture, material balance model was built and matched to the field data Integration of geological and field operational data provided a key to more advanced reservoir management and development strategy optimization. Based on updated reservoir model, new potential drilling targets were identified. Also, with new wells correlation, water flood optimization via management of voidage replacement ratio was proposed. The completed work suggests the essential improvement of reservoir modelling process by inclusion of the various well and reservoir surveillance data. This paper consists of the following sections: Introduction ∘ Field geology ∘ Field development history Scope of work complete and main results ∘ Proposed well logs correlation update for XXI-1’ and XXI-2 layers ▪ Integration of well logs, pressure and fluid analysis data ∘ Connectivity between layers XXI-S, XXI-1’ and XXI-2 ▪ Integration of pressure and oil fingerprinting data ∘ Connectivity within layers XXI-S, XXI-1’ and XXI-2 ▪ Results of pressure interference tests ∘ Testing of new well correlation concept in material balance model ∘ Proposed reservoir correlation based on seismic data ∘ New geological concept ▪ New depositional model ▪ Integration of core data ▪ Changes in reservoir architecture Conclusion ∘ Main results and impact on field development