Nanostructures in tight oil reservoirs: Multiple perspectives

Abstract

This study reveals the heterogeneity, anisotropy, and formation mechanism of nanostructures (pores and throats) for the storage and seepage of tight oil by comprehensively unifying the following techniques: FE–SEM, gas adsorption, EDS, HPMI, MICP, and umbrella deconstruction. The results show that for tight oil reservoirs, 82.8% of the nanoscale pore contributes to oil storage, 50.2% of the nanoscale pore contributes to oil seepage, 76.5% of the nanoscale throat contributes to oil storage, and 38.9% of the nanoscale throat contributes to oil seepage. The nanopores were mainly formed in kaolinite, chlorite, K-feldspar, and illite, with 57%, 21%, 14%, and 7% of the contents, respectively. Among them, 85% are clay minerals. The weathering and dissolution of feldspar contributes a great deal to the formation of nanopores, accounting for about 78%, which a follow-up study should target. The relatively large pores can easily form a relatively large throat, and compaction and diagenesis later have little influence on the density of the nanoscale pores. Simultaneously, the pore radius and throat peak radius are the most robust parameters reflecting the reservoir's storage capacity and infiltration difficulty. The conclusion will provide a crucial scientific basis for tight oil storage and underground flow.