In this paper, the basic concepts of a 3-D random gravel packing modelling technique being developed to simulate typical gravelpack structures are presented. This is a followup on the 2-D modelling technique which was initiated in the Department of Petroleum Engineering at Heriot-Watt University as part of an on-going project On optimum gravel sizing for effective sand control.

The 3-D modelling is based on the simple probability concept in which the gravelpack structure is simulated in three dimensional format by modelling the deposition or settling of gravels one at a time. The resulting gravelpack structure is thereafter evaluated for stability and the resulting pore throat size distribution is evaluated using a purposely developed computer code. The program goes further to evaluate the maximum pore throat distribution and the resulting porosity and permeability of the simulated gravelpack. The maximum pore throat size distribution is here taken as the minimum size of the formation fines that can be effectively controlled by the commercial gravel.

Specific case studies have been carried out for typical commercial gravels the results of which are presented.

Comparisons are made between the 3-D model predictions and those obtained from the preceding 2D model. The 3-D model not only provides a better appreciation of the geometry of the gravelpack structure but also gives a more realistic prediction of pack porosity and permeability when compared with experimental results. The maximum pore throat distribution as predicted by the 3-D model were found to be larger than the equivalent 2-D predictions for all the commercial gravels considered.

Overall, the results have demonstrated that simulation of the gravelpack structure is a very effective technique for probable gravel size selection and is a promising tool for the setting of optimum size distribution criteria for different commercial gravels.

The concept of gravelpack structure simulation forms an integral part of a comprehensive gravel size selection strategy involving the development of a computer package for optimum gravel sizing, a summary of which has also been presented.

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