Abstract

Reservoir evaluation of shaly formations has long been a difficult task. This in turn makes seeking enhanced reservoir description of shaly sand reservoirs much more difficult. This study develops four models and a systematic technique which incorporate conventional log-derived data to identify shale type and hydraulic flow units in shaly sand reservoirs. The four models were derived using available shale models: laminated shale, dispersed shale for low and high shaly formations, total shale, and the Waxman-Smits (W-S) "Cation Exchange Capacity" model. It is found that these four models possess common features in that each flow unit in any shaly sand reservoir can be represented by a straight line on a log- log plot of the "Shaly Reservoir Quality Index" (SRQI) versus porosity. This straight line representing the flow unit yields a unique slope that equal: [1.7 + (m/2)] for laminated shale, [1.7] for dispersed shale, [1.7 + (m/2)] for total shale model, and (1.7+m) for Waxman-Smits model. In addition, each flow unit has a characteristic intercept at (= 1.0 which is equal to the "Shaly Flow Unit Factor" (SFUF).

This study also includes how to apply these models in order to define the shale type and identify different flow units constituting the shaly sand reservoir.

These shaly sand models were validated using a simulated well-log data. The new models, in combination with the technique proposed in this study, represent an effective tool for an enhanced reservoir description of shaly sand reservoirs. In addition, it provides an economical technique due to its inherent use of conventional well log-derived data

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