Reservoir Quality Vertical Heterogeneity Characterization in Shale Oil Reservoir, a Case Study from Junggar Basin

Compared with the marine shale oil resource conditions in the United States, the lacustrine shale oil resource conditions in China are different and the lithology is complex. At present, PetroChina has successfully conducted shale oil horizontal well exploration in such strata as Fengcheng Formation in MaBei, Xinjiang, Kong2 member of Cangdong sag in Bohai Bay, and Qingshankou in Songliao basin has made some progress. However, the understanding and evaluation of "sweet spot" are not perfect, which results in some misleading information for current shale oil exploration, and it brings great challenges to test layer selection and horizontal well landing window selection. Vertical heterogeneity places additional obstacles for reservoir characterization. This paper introduces an integrated methodology for reservoir quality vertical heterogeneous characteristic identification and evaluation in shale oil reservoir by integrating advanced spectroscopy, 2D nuclear magnetic resonance (NMR), and borehole electric image data. Vertical heterogeneity for reservoir quality characteristics includes mineralogy and lithology, rock texture, total organic carbon (TOC), porosity and pore structure, and water saturation. Mineralogy and TOC difference was recognized by the advanced spectroscopy logging data. Rock texture was defined with an innovative edge detection method to identify the lamination status throughout the reservoir. T1-T2 based 2D NMR will solve for porosity, pore size distribution, and fluid identification. Case studies are presented from a shale oil reservoir in the Junggar Basin of Western China. Vertical variety inside the Fengcheng Formation is well defined based on several specs in this case study, including mineralogy and lithology, kerogen distribution, porosity and pore size distribution, and oil-water distribution; the reservoir producibility index was further calculated based on integrated analysis. From the vertical heterogeneity recognized from the above methodology, the sweet spot and horizontal well landing window was successfully recognized. In this paper, we discuss a novel combination of advanced logging methods in unconventional reservoirs, which can help the operators to analyze the reservoir quality vertical heterogeneous character of these reservoirs. The fine reservoir evaluation process helps to define the best oil zones, which will help ascertain the potential of the reservoir and boost the promising oil production. The integrated workflow illustrated in our case studies can be applied and extended to the exploration of other unconventional reservoirs in China.