HSIR-ME-CPMG: A High-Resolved Pulse Sequence for the T₁ - T₂ Measurement of Unconventional Reservoir Rocks

• Published in: IEEE geoscience and remote sensing letters Vol. 21; pp. 1 - 5
• Main Authors: Ge, Xinmin, Miao, Quansheng, Li, Nan, He, Yufei, Xing, Lei, Liu, Baodi, Zuo, Fu
• Format: Journal Article
• Language: English
• Published: IEEE 2024
• Subjects: Correlation; Hybrid saturation recovery and inversion recovery and the multiple echo-spaced Carr–Purcell–Meiboom–Gill (HSIR-ME-CPMG) pulse sequence; improved resolution; Kernel; numerical analysis; Pulse measurements; Reservoirs; Rocks; Sea measurements; Time measurement; T₁ – T₂ correlation map; unconventional reservoir rocks
• ISSN: 1545-598X
• DOI: 10.1109/LGRS.2024.3372526

We designed an improved pulse sequence combined with the hybrid saturation recovery and inversion recovery and the multiple echo-spaced Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence (HSIR-ME-CPMG) to measure the longitudinal relaxation time (<inline-formula> <tex-math notation="LaTeX">T_{1} </tex-math></inline-formula>) and the transverse relaxation time (<inline-formula> <tex-math notation="LaTeX">T_{2} </tex-math></inline-formula>) simultaneously to overcome the shortcomings of conventional IR-CPMG and SR-CPMG pulse train acquisition time and low image resolution. The longitudinal relaxation time (<inline-formula> <tex-math notation="LaTeX">T_{1} </tex-math></inline-formula>) is encoded using the combination of the saturation recovery and the inversion recovery (IR) pulse sequence to improve the resolution between different relaxation components. The transverse relaxation time (<inline-formula> <tex-math notation="LaTeX">T_{2} </tex-math></inline-formula>) is encoded by the CPMG pulse sequence. To reduce the energy consumption and the data storage space, the echo spacing is varied in different windows. Numerical simulations show that the proposed pulse sequence can capture the contrast between different components with similar relaxation times, even in low signal-to-noise ratio (SNR). The proposed pulse sequence can be popularized for better characterizing relaxation components of unconventional reservoirs, such as the shale oil.