Lithofacies Classification of Thin Layered Reservoirs Through the Integration of Core Data and Dielectric Dispersion Log Measurements

摘要

Distal turbidites consist of thin laminations(inch-scale)usually ranging from fine sand to clay-rich deposits and may represent major hydrocarbon reservoirs:conventionally,they are studied by means of a log-based binary modeling that discriminates productive and non-productive layers.Nevertheless,the binary model represents a major drawback when dealing with laminations in the silt grain-size range,as their allotment to either end-member can be extremely problematic. This paper deals with a novel lithological facies classification approach that integrates core data and a high-resolution dielectric dispersion wireline log:its 1-inch vertical resolution and a related fit-for-purpose petrophysical model make the log tool’s response suitable to describe the lithological heteroge-neity of these reservoirs. The approach is presented by means of a study performed on the cored section of a well drilled into a laminated gas-bearing Pleistocene reservoir in the Adriatic Basin.A core-based classification was first carried out using sedimentological descriptions,mineralogical analyses,cation exchange capacity mea-surements,routine and special core analyses,and a statistical investigation of grain-size distributions:this allowed the identification of four litho-facies ranging from hemipelagite to coarse silt.Next,a log-based classification was carried out with a multivariate statistical numerical technique(cluster analysis)run on the dielectric dispersion model output curves along the cored section of the well.In the end,a four-facies log-based classification was obtained that matches the core-based classification with an overall agreement in excess of 93%. When compared to the conventional methodology,the presented approach shows the added value of identifying intermediate lithologies,thus leading to a more accurate quantification of the thickness of the potentially hydrocarbon-bearing net reservoir.