| Popis: |
The Yufutsu field is a fractured granite, gas condensate reservoir, located on Hokkaido island, in the north of Japan. There is minimal primary porosity and secondary porosity consists of fractures. Fractures are categorised into four types according to size (mega, major, minor and halo fractures). Mega fractures govern the flow, while micro fractures govern gas storage. Gas migrated into the reservoir after the fractures were formed. The field shows abnormal production behaviour, and this paper attempts to characterise production, by the use of 3D-stochastic geological modelling and reservoir simulation. Incorporating all of the effects that were observed from the Yufutsu field into a reservoir model proved to be an extremely complex process. A three-stage reservoir study was undertaken: To build a 3D stochastic geological model. Initially small-scale models were built, with both mega and micro fractures modelled stochastically as objects. Effective permeability (matrix + fracture) was calculated across a 200,000 cell single porosity simulation model, along with tracer efflux rates for relative permeability calculations. The above model behaviour was replicated in a 6 cell dual porosity model, which was substituted into the coarser scale single well and full field models. The resultant methodology used provided accurate and realistic description of the fracture system, which was then used for well planning and production forecasting. |
