Determine Oil and Water Saturations in Preserved Source Rocks From 2D T1-T2 NMR

2D T1-T2 NMR has been widely proposed as a method to determine the fluids present in unconventional source rocks. However, the assignment of the components in the 2D T1-T2 NMR has so far been based on conceptual consideration and lacks rigorous experimental verification. Therefore, many of the assignment variations appearing in the literature can be misleading. For example, large T1/T2 peaks in the 2D T1-T2 NMR have been suggested to be fluid in small pores coupled with kerogen through dipolar relaxation. Our recent thorough 500 MHz NMR relaxation experiments found that the dipolar relaxation between nanoconfined fluids and the solid matrix is not large enough to explain the measured T1/T2 result. The objective of this paper is to determine what quantitative data can be obtained using 2D T1-T2 NMR from source rocks with high confidence. We found the oil and water saturation can be accurately measured in preserved source rock plugs. 2D T1-T2 NMR data were collected on 66 preserved plugs from five wells of a source rock reservoir using an Inversion-Recovery CMPG pulse sequence on a 12-MHz NMR instrument. The acquired 2D data were inverted using an optimized inversion software: MUPen2D. We then obtain oil and water saturation from the 2D T1-T2 NMR using an in-house developed NMR MATLAB App. The porosity of all the plugs was measured using a combined NMR and gas porosimetry (CNG) method. Oil and water saturation were also obtained using an industry-standard method developed by Gas Research Institute (GRI) on the rock material close to where the plug was drilled. The oil and water saturations measured on the preserved plugs using 2D T1-T2 NMR and CNG were consistent with those from the GRI method using crushed rocks and an invasive cleaning procedure. The results show that oil and water saturations were accurately determined from 2D T1-T2 NMR on preserved source rock samples with high confidence. The measured results can be further used to determine the production potential of a source rock well in combination with log data. The NMR method is nondestructive and noninvasive and takes less than 4 hours on a preserved source rock plug, while GRI is destructive and invasive and can take several weeks for an accurate measurement on one sample. High-field data of relaxation measurements were applied to low-field T1-T2 maps to further understand the components in the source rock system.