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Utilizing Well Bore Data to Characterize Non-Matrix Pore Types in Carbonates


Pore types in carbonates range from micron-scale voids to meter-scale non-matrix pores that include faults, fractures, and karst features. Where present, non-matrix pores can have a profound impact on reservoir architecture that ultimately affects field development strategies and predictions on wellbore and field performance. Estimated total hydrocarbon in-place may be underestimated if the pore volume associated with non-matrix features is overlooked. Similarly, excess permeability and connectivity associated to non-matrix can lead to a number of unforeseen outcomes including wells with high productivity index, early water breakthrough, and poor sweep efficiency. Although such reservoir challenges are well recognized, understanding how non-matrix features are distributed and, more importantly, how these features impact flow remains problematic. In order to optimize characterization efforts around non-matrix in carbonate reservoirs, we have developed a field-based, integrated approach on San Salvador Island, Bahamas, to identify, characterize, and quantify the non-matrix component of the pore system. Utilizing conventional core and borehole image logs, we have developed a methodology that captures detailed information about non-matrix pores including vertical distribution, feature type, openness, fill properties, and size. This information is combined with dynamic data, such as pressure surveillance, to evaluate how various non-matrix features impact flow at different scales. While non-matrix typically accounts for less than about 10% percent of the total pore volume in a reservoir, its impact on flow can dominate regions of a producing field, suggesting that such observations should be critical in guiding decisions related to field development, well planning, and reservoir management.