Practical approach to achieve accuracy in sanding prediction
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Sand production is a major concern for many operators. It can impact production, cause erosion in downhole and surface facilities, require additional separation and disposal, and lead to significant economic loss. On the other hand, precautionary but unnecessary sand prevention will mean unwarranted reduction in productivity. Reliable sanding prediction analysis thus provides a basis for designs that achieve appropriate sand management strategies and maximization of economic production, and overestimates or underestimates of sanding risk increase the chances of serious economical loss. This raises the question of how accurate and reliable sanding predictions might be achieved without overcomplicating the analyses and without requiring complex lab and field data that, in most instances, will be unavailable or the acquisition of which will incur unwanted delays and costs. This paper presents the case of a sanding study for the Messla field in Libya; a field that has produced oil for more than 30 years. This field experiences massive sanding from some wells but experiences no problems with other wells. This variation made the Messla field an ideal candidate for a detailed sanding and geomechanics investigation aimed at optimizing completions and production and at dramatically reducing the current sanding without having to enter into a lengthy data acquisition programme or time-consuming modelling. In this study, sanding prediction analyses were conducted using a technique that combines easily measurable lab data, log data, and analytical calculations with empirical methods that are supported by the results from previously run rigorous and advanced numerical code. The result of this integration is a sanding analyses tool that uses input parameters such as rock strength, geostresses, and particle size to: account for plasticity effects that modify the strength behaviour of sands surrounding openhole wells and perforations during drawdown to reduce uncertainty and conservatism such as seen in simple elastic models, account for scale effects associated with different perforation and borehole diameters, provide a significant improvement and predictive capability over simple empirical methods, provide the above accuracies without needing complex or extensive lab programmes to determine advanced rock mechanics properties. The application of this approach to the Messla field and a later comparison of the results to actual field data and observations validated the analyses and methods used. The application and comparison also disclosed that the approach was not only able to provide results that closely matched field experience but was also able to predict correctly, to the year, the onset of sanding in wells. This paper describes the methods employed in this investigation, provides details of the data acquisition and processing required, and demonstrates that accurate sanding predictions can be achieved by focusing effort on certain input data, targeting and reducing specific uncertainties, and by employing pragmatic models that do not rely on over-complicated measurements and analyses. Copyright 2006, Society of Petroleum Engineers Inc.
