In coalbed methane (CBM) projects, conventional log such density has been used heavily for coal identification, coal property derivation and also potentially for coal ranking. This paper presents a novel workflow of density log normalization for CBM wells. It addresses two major challenges to current normalization methods, namely, absence of a pervasive reference layer, and removal of geological effects after normalization.
To overcome these disadvantages, the proposed workflow undertakes six steps, which are data quality control, geological area segmentation, sub-area type well selection, density control points, variable linear transformation and quality control of log normalization results using box plots, matrix crossplots and histograms. This workflow removes the systematic errors caused by acquiring logs at different times with different logging instrument from different vendors. Furthermore, it possesses the advantages of automated quality control, Type Well Method and Reference Layer Method without incurring their respective disadvantages. It has been applied successfully to about 600 wells in the Surat Basin of Australia.
Proper log normalization will reduce the uncertainties involved in geological modeling and increase the accuracy of reservoir evaluation. This paper should therefore be of interest to petrophysicists and geologists involved in CBM field characterization.