I. Introduction
For petroleum exploration and engineering, the discrimination of the borehole lithology is extremely important since it is the foundation for further formation evaluation and reservoir characterization. Through the observation and analysis of borehole cores or drilling cuttings, lithology conclusions of subsurface formation can be obtained directly. However, borehole cores are generally expensive since drill cuttings have drawbacks in measuring depth error and thin-layer resolution. As a result, borehole lithology columns obtained by these methods cannot be applied widely.