Shale gas remains one of the hottest topics in the petroleum industry. Petrophysical characterization is an important step for a new shale gas play to better understand the geology of the formation, and it provides vital data to optimize production plan and stimulation design. However, there is little research on correlations between petrophysical parameters for shale gas reservoirs.
The methodologies involved in this study include experimental study, outcrop observation, statistical analysis, and numerical modeling. The Longmaxi shale formation, which is an emerging Lower Silurian marine shale play in China with huge potential according to preliminary explorations, was characterized petrophysically in detail, and research on correlations between different petrophysical parameters was conducted. More than 100 ft core samples were collected from target layers for experiments. Also, the reservoir properties of the Longmaxi shale were compared with those of shale gas plays in the United States, such as the Barnett and Marcellus. Furthermore, based on a robust in-house simulator exclusively for shale gas, a reservoir model was developed by integration of those available petrophysical data to evaluate the key production drivers for typical shale gas reservoirs.
After integrating results from all these methodologies and technologies, total organic content (TOC), vitrinite reflectance (Ro), porosity, permeability, mineralogy, and gas content were obtained. Then, analysis was carefully conducted, and some interesting observations were found, such as an intimate correlation between the clay content and desorbed gas content. Additionally, both similarities and differences between petrophysical properties were concluded from comparison between the Longmaxi Shale and shale gas plays in the US. Moreover, Simulation results quantified the effects of natural fractures and desorption for the production performance.
This study provides a methodology for understanding and characterizing other shale plays. In addition, it offers detailed evidence to support engineers and geologists for understanding the geology and optimizing production plan on the marine shale.