Pore Structure Characterization and Reservoir Evaluation of Lacustrine Organic-Rich Shale Based on the Nuclear Magnetic Resonance Test

Taking the organic-rich shale in the Maye 1 well of the Fengcheng Formation in Junggar Basin and the Chang 73 subsection of the Yanchang Formation in Ordos Basin as the research objects, the samples were tested for pyrolysis of rocks, total organic carbon (TOC) content, X-ray diffraction (XRD), dentification of clay minerals, and one-dimensional and two-dimensional nuclear magnetic resonance (NMR) to carry out studies of pore structure and fractal characterization. The results show that the shale of the Fengcheng Formation develops micropores and small pores, and the shale of the Chang 73 subsection of the Yanchang Formation develops medium and large pores. Dmin and Dmax represent fractal characteristics of bound fluid and movable fluid pores, respectively. The average value of Dmin is 1.54 and that of Dmax is 2.81 in the Fengcheng Formation, and the average value of Dmin is 0.93 and that of Dmax is 2.92 in the Yanchang Formation. The Dmin of the Fengcheng Formation is positively correlated to the porosity and negatively correlated to the TOC and feldspar content. The Dmin of Yanchang Formation is positively correlated with the porosity and TOC; the Dmax is positively correlated with the feldspar content and negatively correlated with the porosity and TOC. We establish a 2D NMR pore fluid component analysis method and a standardized template for identification and realize accurate identification of pore fluid components in shale oil reservoirs (clay-bound water, asphaltene, capillary-bound water, adsorbed oil, free oil, free water). It is found that the bound water and asphaltene contents in the Fengcheng Formation are low, while the average of the Yanchang Formation is higher. The bound and free oil contents in the Fengcheng Formation are higher than those in the Yanchang Formation, while the free oil in the Yanchang Formation has longer T1 and T2 relaxation times and better mobility.