A logging-curve separation scale overlay method for total-organic-carbon estimation in organic-rich shale reservoirs

Abstract

Quantitative estimation of total organic carbon (TOC) content using well logs is very important for shale-gas reservoir evaluation especially when core data is limited.Even though many techniques have been developed to calculate TOC from well logs, they all have their limitations and accurate assessment of TOC in organic-rich tight shales is still challenging. This paper presents an improved log-overlay method for evaluating TOC content in organic-rich tight shale reservoirs by overlying the properly scaled GR, DT, DEN curves on top of the CNL curve based on the same concept to the original ∆logR technique. These logging curves are overlapped with the CNL in non-source intervals and are separated in organic-rich shale reservoirs. The separation magnitude increase along with the increase of TOC content of the shale and this relationship is transformed to calculate TOC. This method was tested and verified by doing a case study using well-log data from the Jiaoshiba tight shale-gas play in the Sichuan Basin. The results show that the new TOC evaluation method is more practical and effective compared with existing TOC evaluation methods.

Effective Attributes Quantification to Bridge Gap between Elastic Properties and Reservoir Parameters in Self-Resource Rocks

“…Generally, well logs are used to quantify organic matter and to do so several methods have been proposed by different researchers [5][6][7] . The brittleness index can be inferred through elastic properties or minerals content of the rock 8 .…”