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

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 (
$T_{1}$
) and the transverse relaxation time (
$T_{2}$
) simultaneously to overcome the shortcomings of conventional IR-CPMG and SR-CPMG pulse train acquisition time and low image resolution. The longitudinal relaxation time (
$T_{1}$
) 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 (
$T_{2}$
) 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.