Pore Connectivity Characterization of the Wufeng and Longmaxi Shales From Sichuan Basin, China Using Wood’s Metal Intrusion and High-Resolution 2-D and 3-D Imaging

Abstract

Much attention have been paid to the Upper Ordovician Wufeng and Lower Silurian Longmaxi formation shales in the Sichuan Basin after the recent successful commercial development of shale gas in China with numerous publications on the characterization of the shales in various aspects. However, there has been little done with reference to the pore connectivity of the shales, paricularly in three dimensions. We investigated and compared the pore connectivity among different types of shales within the Wufeng and Longmaxi formations by coupling Wood’s metal alloy intrusion at high pressure and high-resolution 2D and 3D imaging using SEM and micro- and nano- scale X-ray CT tomography. Our in-house designed metal alloy intrusion device has a maximum pressure of up to 350 MPa, corresponding to a pore throat diameter of approximately 4 nm. The Wood’s metal alloy in the interconnected nano-pore network provides excellent contrast against the background minerals and organic matters under SEM and X-ray CT, allowing the easy and effective delineation of the connected pore networks. The results indicate that micro- or nano- fractures and interparticle inorganic pores provide the dominant connectivity despite the organic matter pores (OM pores) privide the major storage space. Calcareous shales show excellent connectivity with the presence of well-developed interparticle pores, capable of effectively connecting ink-bottle-like OM pores. In contrast, siliceous shales show an overall poor connectivity with only a small amount of OM pores immediately adjacent to micro fractures displaying interconnection. The three-dimensional morphology and pore structure parameters revealed from the metal alloy intrusion experiments provide further useful information on muti-scale characterization of pore connectivity and upscaling for hydrofracturing.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018