Pore structure and fluid distribution of tight sandstone by the combined use of SEM, MICP and X-ray micro-CT

Tight reservoirs contain considerable hydrocarbon resources, which are characterized by complicated pore structure and heterogeneous fluid distribution in the pore network. In this study, a tight sandstone sample from the Lucaogou Formation in the Jimsar Sag was selected for the characterization of pore structure and two-phase (brine and oil) flow experiment. Interparticle and intraparticle pores were identified and quantified by direct image analyses. Intraparticle pores, commonly smaller than 1 mu m, were the dominant contributor of surface area, whereas interparticle pores contributed considerably to pore volume with minor quantity. Pore network model of the selected sample was featured by large pore throat ratio, which was also verified by low efficiency of mercury ejection (approximate to 1.66%). The flow potential of tight reservoir was dominantly controlled by pore-throats with a diameter larger than 2 mu m. Based on the results of pore-scale micro-CT flow experiments, the configuration of oil clusters in the pore space was categorized into singlet, multiple, branched and network. The size of oil clusters ranged over five orders of magnitude (10 mu m3 - 106 mu m3), which followed a power-law distribution. The displacement process of water by oil in the pore space of tight sandstone was controlled by pore structure and external driving force. The well-connected pore network mainly composed of large interparticle pores was the preferential flow path, and a high proportion of singlet oil clusters was attributed to high aspect ratios of the pore network. As the external driving force increased, convergence and divergence of oil flow occurred simultaneously in the pore network. The displacement process of water by oil was suggested as a cooperative pore-filling event.

Automated summary

This study characterized the pore structure and two-phase (brine and oil) flow experiment of a tight sandstone sample from the Lucaogou Formation in the Jimsar Sag, identifying interparticle and intraparticle pores, as well as the configuration and displacement process of oil clusters in the pore space. The pore-throat ratio and pore size were found to control the flow potential of the reservoir, with oil displacement by water suggested as a cooperative pore-filling event.