Effective field development planning for giant fields as big as Samotlor in Western Siberia faces a number of challenges. Samotlor field has almost 50 years of production history, and is known for its complex multi-reservoir geology, active gas cap, sophisticated waterflood program of giant proportions, and has more than 14 thousand wells. The field of such complexity and magnitude cannot be developed without a full-field hydrodynamic model covering the entire reservoir.
Historically, due to extreme complexity, only highly upscaled models have been used. These models were primarily used for calculation of the remaining reservoir energy, material balance analysis, gas cap migration, but never had enough spatial resolution to allow for simulations at the well level.
To make plans for infill drilling and various workovers, the most production units were relying on sector models, which did have necessary spatial resolution, but had obvious limitations in the areal coverage of the field. As a result, due to the differences in grid resolutions, the results obtained from history matching of sectors were rarely used for full-field model causing frequent inefficiencies and redundancies in simulation workflows.
In a course of planning work to develop the remaining oil reserves of Samatlor field, a new “unified model” concept has been developed. In this concept, one and the same model is being used both for global optimization of full-field model as well as for making decisions at the level of individual wells. To determine optimal grid resolution, models with 5, 40, 160 and more than 400 million active grid blocks were selected, and simulation results compared. For the first time, a new hydrodynamic model based on un-upscaled geological grid of AV1-5 reservoir group of Samotlor field was simulated. By taking into account the number of wells and the length of the production history, this is probably the most complex simulation of reservoir dynamics ever attempted in the oil & gas industry.
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