Abstract
The shale gas potential of Ediacaran and Lower Silurian shales from the Upper Yangtze platform is assessed in this study with a focus on the contributions of clay minerals and organic matter to sorption capacity. For this purpose, a multidisciplinary assessment was carried out using petrophysical, mineralogical, petrographic and geochemical methods. In terms of TOC contents (4.2%), brittle mineral contents (68.6%) and maximum gas storage capacities (0.054–0.251 mmol/g) Ediacaran shales from this study show comparable properties to other producing shale gas systems although the thermal maturity is extremely high (VRr = 3.6%). When compared to lower Silurian shales from the same region, it is evident that (1) deeper maximum burial and (2) a lack of silica-associated preservation of the pores resulted in a relatively lower mesopore volume, higher micropore volume fraction and lower overall porosity (Ediacaran shales: 1.4–4.6%; Silurian shales: 6.2–7.4%). Gas production is therefore retarded by poor interconnectivity of the pore system, which was qualitatively demonstrated by comparing experimental gas uptake kinetics. TOC content exhibits a prominent control on sorption capacity and micropore volume for both shales. However, different contributions of clay minerals to sorption capacity were identified. This can partly be attributed to different clay types but is likely also related to burial-induced recrystallisation and different origins of illite. Additionally, it was shown that variations in sorption capacity due to incorrect estimates of clay mineral contribution are in the same range as variations due to differences in thermal maturity.Article highlightsPore structure and gas storage characteristics are evaluated for the first time for Ediacaran Shales from the Upper Yangtze platformDue to a lower free gas storage capacity and diffusivity, the Ediacaran shale can be regarded as a less favorable shale gas prospect when compared to the Silurian shaleClay mineral contribution to sorption capacity is evaluated taking clay mineralogy into considerationMaturity-related changes of organic matter sorption capacity have been discussed on the basis of a compiled data set
Highlights
Shale gas production in China progressed fast from 0.025 billion cubic meter in 2012 to 10.88 bcm in 2018 but is still in an initial stage when compared to the United States (624.40 bcm in 2018) (Zhai et al 2018; Wang et al 2019; Dai et al 2020)
(Ghanizadeh et al 2014; Fink et al 2018), this observation can be regarded as a first indication of a less favorable pore structure of the Ediacaran shales with respect to long-term production when compared to the Silurian shales
High-pressure CH4 sorption, low-pressure N2 / CO2 adsorption and water immersion porosimetry measurements were performed on Ediacaran (Liuchapo and Doushantuo formations) and Lower Silurian (Longmaxi formation) shales from the Upper Yangtze platform to characterize and compare pore structures as well as maximum methane storage capacities
Summary
Shale gas production in China progressed fast from 0.025 billion cubic meter (bcm) in 2012 to 10.88 bcm in 2018 but is still in an initial stage when compared to the United States (624.40 bcm in 2018) (Zhai et al 2018; Wang et al 2019; Dai et al 2020). When compared to the average gas production rate (12.87 9 104 m3/day) and total gas content (1.9–8.0 m3/t or 0.083–0.352 mmol/g at IUPAC conditions) of the Wufeng and Longmaxi shale formations (Zou et al 2014, 2016), these test wells indicate good exploitation potential of Proterozoic shales in the Yangtze platform. (2021) 7:71 studies far focused on shales from the Ediacaran (Chen et al 2016; Yang et al 2020) These shales, though extremely high in thermal maturity (approximately 4.0% in equivalent vitrinite reflectance), are rich in organic matter (TOC content of up to 8.0 wt.%) and widely distributed in the area of the Upper Yangtze platform with thicknesses of 200 to 900 m. The well-studied Silurian Longmaxi Shale in the Sichuan Basin has a lower thermal maturity (2.0–3.2%), smaller thickness from 100 to 500 m, exhibits high TOC contents (up to 8.3 wt.%) as well as porosity (3.4–8.2%) (Zou et al 2014; Yang et al 2015; Zhang et al 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Geomechanics and Geophysics for Geo-Energy and Geo-Resources
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
