Organic matter detection in T1-T2 relaxation maps for shale reservoirs

VELASCO, MANUEL I.; SILLETTA, EMILIA V.; VILA, GABRIELA S.; DOMENÉ, ESTEBAN A.; BEDINI, PAULA; GARRO LINCK, YAMILA; FRANZONI, MARÍA B.; MASIERO, DIANA; MONTI, GUSTAVO; ACOSTA, RODOLFO H.

Hangzhou

Conferencia; 15th International Bologna Conference on Magnetic Resonance in Porous Media (MRPM15); 2022

Quantification of organic matter and fluids contained in oil source rocks from shale plays is a fundamental goal for the petrophysical and geochemical assessment of the production potential of a well. Laboratory 1H nuclear magnetic resonance (NMR) is a fast, reliable, and non-destructive method widely used in the oil industry. Measurement of T1-T2 correlation maps have been found to be critical for identifying the presence of solid organic matter, liquid hydrocarbons, and brine in these formations. However, the inherent long echo times associated with standard laboratory equipment for large sample volumes is challenging for the detection of kerogen and viscous bitumen [1]. In this work, we implement a T1-T2*&T2 pulse sequence to enable the detection of solid organic matter by acquiring the free induction decay after the first excitation pulse, followed by a CPMG pulse train [2,3]. To aquire the T1 dimension, Saturation-Recovery showed a better performance than Inversion-Recovery sequence. This development was used to study samples from the Vaca Muerta Formation in the Neuquén Basin, Argentina, with a broad range of total organic carbon (TOC) as received.Fig. 1a shows the T1-T2 relaxation map for a shale sample extracted from a well in the oil production window, using the SR-CPMG sequence. Due to the long echo-time (tE = 200 µs), only components with relaxation times longer than 100µs are detected. The signal coming from solid-like components (including organic matter) decays faster and those contributions do not appear in the map. Using the proposed sequence (SR-FID-CPMG) the FID decay is also measured. Contributions with shorter T2 values are present as shown in Fig. 1b. Regions 1 and 2 correspond to organic matter. Region 3 is assigned to clay-bound water while region 4 corresponds to liquid hydrocarbons. The inclusion of a Hahn echo prior to the CPMG detection was also implemented (SR-FID-ECHO-CPMG) to extend the FID acquisition period