Abstract
This paper details a micro-laminated sand fluid substitution algorithm developed by Rone Shu at OHM Rock Solid Images. Fluid substitution in a laminated sand whose layers are below the resolution of logging tools creates a problem because Gassmann’s equations, the traditional method for fluid substitution, are intended to be used on homogenous rocks. However, in a laminated sand, fluid changes occur only in the sand layers. This leads to an over-prediction of the fluid effect because shale laminations are also being modelled. Alternative solutions to this problem require knowledge of the clean sand and pure shale rock properties, which is not always practical. Our algorithm does not require knowledge of the lithological end-member rock properties, can be applied quickly and efficiently, and is of similar accuracy as more rigorous methods. We illustrate the method and results with a case study. The reservoir section is a turbidite that has a prominent oil-water contact. We fluid substitute the lower (wet) portion to similar reservoir conditions as the upper (hydrocarbon-saturated) portion using both the standard Gassmann algorithm as well as the new laminated sand algorithm. The results show accurate fluid substitutions with the new algorithm but significant over-prediction with the traditional Gassmann approach.
Published Version
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