Estimating the permeability of reservoir sandstones using image analysis of pore structure

摘要

In this thesis, a method is developed for predicting the permeabilities of a core usingudonly a small number of SEM images, without resorting to computationally intensiveudprocedures. The pore structure is idealised as consisting of a cubic network of poreudtubes having an arbitrary distribution of cross-sectional areas and shapes. The areas andudperimeters of the individual pores are estimated from image analysis of scanningudelectron micrographs of thin sections, with appropriate stereological correctionsudintroduced to infer the true cross sections of the pores.udEffective medium theory is used to find the effective single-tube conductance, basedudon the measured distribution of individual conductances, thereby allowing a predictionudof the permeability. The methodology has been applied to several reservoir sandstonesudfrom the North Sea, and also an outcrop sample from Cumbria, UK, yielding predictionsudthat fall within a factor of two of the laboratory measurements in most cases.udThe procedure, although based on Kirkpatrick's intrinsically isotropic effectivemediumudapproximation, is not only capable of yielding reasonably accurate estimates ofudthe permeabilities, but also gives a qualitatively correct indication of the anisotropyudratio. It also found that the use of an Bernasconi's anisotropic effective-mediumudapproximation does not lead to a systematic improvement in the results, perhaps becauseudthe samples used in this study were insufficiently anisotropic for the approaches to yielduddifferent results.udThe validity of the effective medium approximation was also tested against exactudpore network calculations. For the rocks examined in this study, with pore conductanceuddistributions having log-variances less than 3, the effective medium approximation wasudfound to be accurate to within a few percent.