Application of a lithofacies model to characterise the gas shale in the Wufeng and Lungmachi formations,NE Sichuan Basin,China

Abstract

A practical model that uses a combination of the variations in total organic carbon (TOC) content and mineralogy is developed to determine the shale facies. By using a ternary plot, four main lithofacies and 14 subfacies were identified. This method is applied to describe the shale lithofacies and to identify the favourable lithofacies in the Wufeng and Lungmachi formations based on drill cores from well WX2, NE Sichuan Basin, China. The results show five classes of lithofacies are present and the organic-rich siliceous shale at the base of the Lungmachi Formation (LMF) is the most promising lithofacies, as it has the highest in-situ gas content, abundant TOC, and a high brittleness index, which are all favourable for the generation and development of shale gas. No significant changes in lateral continuity exist in the study area. The core based model can be used to quantify shale lithofacies in other areas.