Optimization of two-dimensional T1–T2 relaxation correlation measurements in shale

Shale reservoirs, composed of fine-grained and organic-rich sedimentary rock, are common unconventional oil and gas reservoirs. Magnetic resonance (MR) relaxometry, a non-destructive and non-invasive method, is a key technique for shale evaluation. The T1*–T2* relaxation correlation, a rapid two-dimensional MR measurement, is a newly emerging and powerful tool to study the structure of materials with short transverse relaxation times. T1* and T2* are the effective longitudinal and transverse relaxation times. T1*–T2* measurement is a promising laboratory method to analyze fluid and organic matter components in shale, but it is very sensitive to the acquisition parameters. In this paper, the effects of acquisition parameters, including flip angle α, initial interval τ1, α pulse interval τ, and scan number, on T1*–T2* relaxation correlation of shale were analyzed by numerical simulations and core plug experiments. The optimized T1*–T2* measurement can be two orders of magnitude faster than a simple T1–T2* measurement. This work provides a theoretical and practical guide for undertaking T1*–T2* measurements, which should be helpful for further laboratory study of shale. •Rapid T1*–T2* measurements based on Look-Locker sequence is performed for shale.•Properties of the sample suitable for T1*–T2* measurement are introduced.•Effects of acquisition parameters on T1*–T2* measurements of shale are analyzed.•Low α, short τ1, and medium τ are recommended for shale T1*–T2* measurements.•Optimized T1*–T2* measurement is much faster than a simple T1–T2* measurement.