An integrated assessment system for shale gas resources associated with graptolites and its application

Shale gas exploration or development has been carried out in many countries, and gas shales have become one of the major sources of future natural gas production worldwide. However, many differences of gas shales in China with those in other regions make shale gas development in China exceptionally challenging. Fortunately, the Wufeng-Longmaxi gas shales in China contain abundant graptolites, providing a potential method for evaluating the quality of these gas shale reservoirs in South China. Numerous exploration studies have shown that the shale gas sweet-spot intervals in the Wufeng-Longmaxi Shale coincide with graptolite biozones WF2-LM5, providing new insight for evaluating shale gas sweet-spot intervals. This paper, for the first time, proposes a new integrated method using graptolite zones to identify shale gas sweet-spot intervals. Once the sweet-spot interval of shale gas is determined quickly by using this method in an explored block, it can provide an important reference for well design and hydraulically fracturing treatments within short time, significantly enhancing the efficiency of shale gas exploration. More importantly, this new integrated assessment system can be utilized to quickly judge the potential of shale gas development for new shale gas blocks or poorly explored blocks.