Water Saturation Evaluation in Shaly Sand Reservoirs Using Advanced X-ray Diffraction and Cation Exchange Capacity Measurements

摘要

Interpretation problems are commonly associated with calculating water saturation in non-homogenous shaly sand reservoirs. Recent studies on the electrical anisotropy of shaly sands have shown that the level of our understanding and our ability to correctly and accurately evaluate low resistivity & low contrast pay can be greatly improved. The model (“Expansible Clay Model”) developed in this work is similar in form to the recent shaly sand Dual Water Model. It is an experiment based model designed to directly assess and quantify the effects of the mineralogical and electrical properties of clay minerals in heterolithic reservoirs. Clay minerals usually have multiple effects on petrophysical properties obtained from geophysical well log measurements. The Expansible Clay Model evaluates these effects via direct measurement of independent mineralogy and conductivity of the clay minerals within reservoir sands. The model integrates the following as an effective basis for characterizing shaly sand reservoirs: ? Rietveld based siroquant assay for quantitative X-ray diffraction (XRD) used in determining mineral percentages from standard XRD trace patterns, ? Cation exchange capacity (CEC) used to determine the quantity of cations involved in the exchange at the shale-water interface, ? Porosity, permeability, density and resistivity measurements, Overall, correlations drawn from the model when applied, yields valid results for total water saturation which appeared consistent with those earlier calculated using well known water saturation models (Dual Water and Juhasz). A total of 23 core plugs from two wells in the Cliff Head Field, Perth Basin, were analyzed for this study.