Key factors influencing the low-field NMR characterisation of gas- and oil-bearing shales: a case study of the shales from the southern Sichuan Basin and Dongying sag, China. (20th April 2020)

• Record Type: Journal Article
• Authors: Chen, Chen; Lu, Shuangfang; Zhang, Pengfei; Li, Junqian; Li, Wenbiao; Wang, Siyuan
• Is Part Of: International journal of oil, gas and coal technology. Volume 24:Number 4(2020)
• Page Start: 466
• Page End: 482
• Publication Date: 2020-04-20
• Subjects: shale -- low-field nuclear magnetic resonance -- NMR -- waiting time -- TW -- number of scans -- NS -- grain size -- probe liquid -- echo number -- NECH -- signal-to-noise ratio -- SNR; Petroleum as fuel -- Periodicals; Gas as fuel -- Periodicals; Coal -- Periodicals; Biomass energy -- Periodicals; Hydrogen as fuel -- Periodicals; 662.6
• Languages: English
• ISSNs: 1753-3309

Abstract

The response characteristics of transverse relaxation time ( T2 ) of key experimental parameters [waiting time (TW), number of scans (NS) and echo number (NECH)], sample size and probe fluid, are analysed systematically based on NMR experiments of oil- and gas-bearing shales from the Shahejie Formation in Dongying sag and the Wufeng and Longmaxi Formations in the southern Sichuan Basin. The results indicate that: 1) the optimised NMR parameters for TW, NS and NECH are 1, 500 ms, 64 and 6, 000, respectively, which will ensure higher accuracy and signal-to-noise ratio (SNR); 2) the total signal amplitude of the T2 spectrum increases with decreasing grain size. The T2 spectra of shale which grain size bigger than 10 mesh can characterize the shale PSD; 3) water porosity clearly decreases with increasing brittle minerals but decreasing clay content than n-dodecane-saturated porosity, which indicates the hydration of clay and brittle minerals together controls the reconstruction of PSD. [Received: May 30, 2018; Accepted: October 24, 2018]