Abstract
Carbonate reservoirs in the South China Sea mostly contain natural fractures with various length scales and different intensities, which causes great challenges in efficient reservoir modeling and flow simulation. Existing efforts based on dual-porosity and dual-permeability models could not reflect the characteristics of production data in certain wells. To accurately and efficiently characterize multiscale fractures, a hybrid fracture characterization method is proposed. Firstly, fractures are divided into two types according to the geometrical size and interpretation approach. Then, small-scale fractures, characterized mainly by image log interpretations, are modeled by the traditional dual-porosity/dual-permeability (DP) method. And large-scale fractures, which are characterized by seismic interpretations and dominate the flow regime, are modeled by the embedded discrete fracture method (EDFM) to achieve both accuracy and efficiency. Lastly, transmissibilities among these three types of grid mediums are calculated to generate the hybrid DP+EDFM model for flow simulation. The proposed approach is applied to a carbonate, fractured reservoir in the South China Sea. The overall procedure is fast and reliable, and water cut matches of both field and specific wells are dramatically improved. Comparing the simulation results with the conventional DP model, the proposed approach yields much more accurate predictions on rapid water breakthrough and high water cut in fractured reservoirs.
Highlights
Effective modeling of fractured reservoir remains a challenge since realistic characterization of fractures is difficult, and highly recognized algorithms to derive field-scale fracture properties from seismic processing results are not yet available
In terms of simulation time cost, the DP +embedded discrete fracture model (EDFM) model slightly increases to 11,162 s, which is
(1) A hybrid grid system is generated to precisely and efficiently model both large-scale and small-scale fractures through an integrated approach
Summary
Effective modeling of fractured reservoir remains a challenge since realistic characterization of fractures is difficult, and highly recognized algorithms to derive field-scale fracture properties from seismic processing results are not yet available. Advances in seismic and image log interpretations for fracture mapping have been made for the last two decades, which make quantitative modeling of naturally fractured systems possible. As a result, it is viable, though with significant uncertainty, to represent actual fracture distribution in reservoir modeling and run detailed flow simulation via a discrete approach [1]. Moinfar et al [9] proposed an embedded discrete fracture model (EDFM) to model different scales of fractures all together into a dual-porosity type of media. The target reservoir is an offshore carbonate formation in the South China Sea that has been in production since 1996 It has complex geology and developed faults and fractures. The water cut rapidly increased above 90% by the end of 2001
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