A new method for lithology identification of fine grained deposits and reservoir sweet spot analysis: A case study of Kong 2 Member in Cangdong sag, Bohai Bay Basin, China

Based on systematic coring of 500 m of Kong 2 Member of the Paleogene Kongdian Formation in Cangdong sag of Bohai Bay Basin, identification and XRD (X-Ray Diffraction) analysis of over 1000 thin sections, a simplified method to quantitatively calculate contents of fine grained minerals with conventional logging data such as acoustic travel time (AC) and density log (DEN) has been proposed, and a quick lithologic identification “green mode” has been worked out in this study. By fitting the relationship between normalization of logging curves and mineral content measured by XRD, the mineral contents of sections or wells not cored can be calculated to identify lithology. With this method, several dolomite sweet spot intervals and one sandstone sweet spot interval have been found in the Kong 2 Member of Cangdong sag, where high production oil and gas flows have been tapped from drilled wells. The study shows that the dolomite is in band distribution and enriched in local parts of the study area. This method is applicable to lithologic identification of fine grained deposits in front delta-lake basin center, especially lithologic identification of mud and dolomite dominated fine grained deposits with low sand content of semi-deep, deep lake facies.