No measurement made is ever known to be exact. Accuracy (correctness) and precision (significant digits) of an instrumental measurement (i.e., logging tools and surface laboratory measurement) are subject to the underlying governing physics and the qualities of the apparatus used. As a consequence, every measurement has a range of possible true values and all quantities therefrom derived necessarily carry those uncertainties with them.
In this study, an analysis of the density, sonic and resistivity tools’ associated uncertainty is presented that shows how these measurement related uncertainties propagate forward into conventional overburden and pore pressure gradient calculations. The tool based random uncertainties ultimately create a statistically reliable range for pore pressure estimations.
The implications of this sort of analysis suggests that there is an inherent level of uncertainty in all pore pressure calculations that can never be unless there is some sort of instrumental refinement. Similarly, fracture gradient and wellbore stability calculations also must bear the weight of these uncertainties from derived quantities plus their own contributions. While breakthroughs in analytical technique are likely possible in the future, reduction of the random error by measurement cross-validation and integration is shown to be an achievable outcome without any improvements in the current technology.Limits on the Accuracy of Pore Pressure Estimates by Analysis of Random Measurement Error and Means for Improvement.
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