Diagenesis and diagenetic facies distribution prediction of Chang 8 tight oil reservoir in Maling area, Ordos Basin, NW China

Abstract

In this study, characteristics of Chang 8 tight sandstone pore structure and diagenesis are analyzed. A classification standardfor sandstone diagenetic facies is established. Combined with the probabilistic neural network method, logging curves are used topredict the distribution of diagenetic facies. The following results are found: the Chang 8 reservoir has low porosity-low permeabilitycharacteristics, and the pore-throat structures have strong microscopic heterogeneity; both compaction and siliceous and carbonatecementation promote reservoir densification; chlorite cement lining, hydrocarbon emplacement, and the dissolution of feldspar androck fragments have constructive effects on reservoir development; and two favorable diagenetic facies, a weakly compacted andchlorite-authigenic quartz cementation facies and an intensely compacted-dissolution facies, are developed in the middle of the thicksandstone and are a good match in their horizontal distribution with distributary channel sands. The Chang 81 member has a muchlarger area that is more favorable for the development of reservoir diagenetic facies than the Chang 82 member.