Diagenetic facies quantitative evaluation of low-permeability sandstone: A case study on Chang 82 reservoirs in the Zhenbei area, Ordos basin

Abstract

Quantitative characterization of diagenetic facies has great significance for reservoir evaluation and prediction. In order to find out the method to evaluate diagenetic facies, the author took Chang 82 reservoir low-permeability sandstone in Zhenbei area of Ordos basin as research object and divided the reservoir into six types of diagenetic facies by analysis of casting thin section, scanning electron microscope, cathode luminescence, and physical property. According to 14 quantitative evaluating parameters which were related with petrology characteristic, diagenesis strength, pore structure, etc. quantitative evaluation of diagenetic facies of low-permeability sandstone reservoir was done by data envelopment analysis. The result showed that in the Chang 82 reservoir low-permeability sandstone in Zhenbei area of Ordos basin, quantitative representative indexes of diagenetic facies ranged from 0 to 1.00. Various diagenetic facies and their indexes had interval corresponding relation. The diagenetic facies of weak corrosion with chlorite mat and the diagenetic facies of corrosion of unstable components had the best reservoir quality. Their diagenetic facies indexes ranged from 0.66 to 1.00. The reservoir quality of the diagenetic facies filled with kaolinite was not as good as the former. The indexes ranged from 0.50 to 0.66. The diagenetic facies of quartz secondary enlargement and the diagenetic facies of clay mineral cementation replacement had poor reservoir quality. Their diagenetic facies indexes ranged from 0.30 to 0.40. The diagenetic facies of carbonate cementation had the poorest reservoir quality. It hardly possessed fluid storage capability. After comparing diagenetic facies indexes, absorption strength and remaining oil saturability, the perfect corresponding relation between quantitative evaluation results and reservoir quality could be verified.