Estimation of mean pore-size using formation evaluation and Stoneley slowness

• Derivation of two new empirical models to estimate the pore-size.
• Calibration of the models using the least squares method.
• Assessment of the models in permeable and non-permeable zones.

Continuous estimation of pore-size can be very helpful to use in optimization of well completion and effective production of hydrocarbon reservoirs. This paper shows the application of two new empirical models derived of the Kozeny-Carman equation to estimate the mean pore-size. The models are: The formation evaluation model, and the Stoneley slowness model. The main objective of this work is to give a general framework to develop the number of methods that provide a continuous estimation of formation mean pore-size along the well.In the final form of the derived equations, the calibration factors for minerals were the only constants that had to be determined using a calibration method. Therefore, the proposed models were calibrated with core data using the least squares method. Fortunately, all the required core data were accessible to be used for the calibration process. Moreover, the effects of some parameters such as the shape factor were ignored. The shape factor value is influenced by the pore shape. The calibrated models were then used to re-compute the mean pore-size in the logged intervals. The results showed that, in many points, there was a relatively low difference between the estimated mean pore-size and the core pore-size. According to the calculated calibration factors for two methods, illite had a very negative effect upon the pore-size values among all the minerals. The proposed models could be used as an index for determining the permeable and non-permeable layers. As a result of the calibration of the proposed models (particularly for the Stonely model), the RMSE values calculated for the permeabilities of less than 100 mD were lower than that of the permeabilities of greater than 100 mD. The least RMSE values were calculated for the permeabilities ranged in 10–100 mD. Moreover, the simultaneous assessments of the presented pore-size models, and comparing their results with the core data, helped us to evaluate the correctness of the calculated pore-size as well as the permeability.

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