Nanopores in Longmaxi Formation Shale, East Sichuan Basin, Southwest China

Abstract

Longmaxi Formation shale is a very important shale gas target in east Sichuan Basin, China, which was discovered 200 thousand cubic meters per day of gas production. It had organic pores and mineral pores in the Longmaxi Formation shale, and that natural gas is mainly stored in organic matter pores or mineral pores are becoming the discussed focus. FE-SEM (field-emission scanning electron microscopy), carbon dioxide and nitrogen low-pressure sorption were used to define this problem in ten Longmaxi shale samples with the total organic carbon (TOC) content ranged 1.34 wt% to 6.45 wt% and helium porosity varied from 1.2% to 4.3%. Helium porosity were strongly associated with total organic carbon (TOC) content instead of mineral matrix in the ten Longmaxi shale samples. The porosity detectable by FE-SEM was a small fraction of total porosity, ranging from 18% to 64%, average 60%. Helium porosity undetectable by FE-SEM had the strongly relationship with TOC volume percent, suggesting that most porosity may be associated with TOC. carbon dioxide and nitrogen low-pressure sorption results showed that many pore were lesson than 8 nm in the Longmaxi Formation shale, which could not be captured by FE-SEM, consistent with that most pores may be under the FE-SEM limit. Therefore, organic matter pores may be the dominant accumulation pore types of natural gas in the Longmaxi Formation shale.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015