Nuclear Magnetic Resonance Evaluation Method of Shale Oil with Medium and Low Maturity in Biyang Sag

The pore structure of shale oil with medium and low maturity is complex, and the detection of pore density is difficult. In addition, kerogen, asphalt, and solid-like components are developed, making it difficult to accurately evaluate sweet spots. In order to accurately evaluate the reservoir and oil-bearing characteristics of shale reservoirs with medium and low maturity, low-field nuclear magnetic resonance (NMR) technology was taken as the main research method. The factors affecting the acquisition accuracy of NMR signals, such as magnetic field intensity, probe aperture, echo interval, and peak shift, were compared and analyzed, and the high-precision acquisition parameters of shale oil with medium and low maturity suitable for the development of short relaxation components were determined. The reservoir and oil-bearing characteristics of Well YY1 in Biyang Sag were evaluated by using high-resolution 1D and 2D NMR measurements, combined with the experimental results of nitrogen adsorption, mercury injection, and geochemical analysis, and a characterization model of kerogen content based on 2D NMR components was established. The results show that the NMR measurement of shale oil with medium and low maturity puts forward higher requirements for the echo interval of instruments. Under the condition that T_E cannot be shortened by instrument hardware, more information of short relaxation components can be collected by means of peak shift to obtain more representative spectra. NMR technology can realize the high-precision evaluation of various characteristics of shale oil reservoirs and source rocks with medium and low maturity. It is of great role to carry out in-depth information mining and research for the efficient exploration and development of shale oil with medium and low maturity.