Classification of the tight oil reservoir storage space in the Raoyang Sag of the Jizhong Depression in the Bohai Bay Basin, China

Abstract

AbstractTo improve the precision of predicting sweet spots in tight oil reservoirs, the classification of tight oil reservoir storage space is necessary. The tight oil reservoir in the lower submember of the first member of Shahejie Formation (Es1L) of the Raoyang Sag of the Jizhong Depression in the Bohai Bay Basin was selected as a case study for testing a new method of classifying tight oil reservoir storage space based on the results of porosity, permeability, and mercury intrusion porosimetry measurements. The pore‐throat size ranges were classified according to pore‐throat fractal characteristics and were divided into three groups: <100 nm, 100‐1000 nm, and >1000 nm. The oil‐bearing property of tight oil reservoir samples is closely related to the median and maximum pore‐throat radii. The inflection and intersection points in the trend lines of the pore volume percentages connected by different pore‐throat widths (<100 nm, 100‐1000 nm, and >1000 nm) vs the porosity and permeability values (which represent the relationship between the pore volume connectivity characteristics and porosity/permeability) were used as the basis for classifying the tight oil reservoir storage space. The tight oil reservoir storage space in the Es1L formation of the Raoyang Sag was divided into three categories, namely classes of III, II, and I. The porosity ranges of the three tight reservoir storage space classes are <5%, 5%‐8%, and 8%‐11%, respectively, and their permeability ranges are <0.04 mD, 0.04‐0.15 mD, and 0.15‐0.8 mD, respectively.