Characteristics and origins of the modal pore throat structure in weakly cemented sandy conglomerate reservoirs

Abstract

The pore throat structure of sandy conglomerate reservoirs is more complex than that of conventional sandstone reservoirs. At present, research on the modal pore throat structure of sandy conglomerate reservoirs mainly focuses on tight reservoirs with diagenesis controlled, while research on weakly cemented reservoirs is limited. Taking the newly discovered Cretaceous Guyang Formation reservoir on the western edge of the Hetao Basin as the research object, the modal pore throat structure of this weakly cemented sandy conglomerate reservoir is studied. The petrological and pore throat characteristics are studied by performing various tests. Based on the inflection points of the multifractal curve of the pore throat radius of the studied sandy conglomerate reservoir, the pore throat structures of a sample are divided into three types: macrothroats, mesothroats and microthroats. The pore throat structures of every sample are composed of these three pore throat structures. The heterogeneity at the microscale is controlled by the proportions of these three pore throat types. Based on the proportions of macrothroats, mesothroats and microthroats, the modal pore throat structures of the studied sandy conglomerate reservoir are analyzed for the first time. The modal pore throat structures of the corresponding samples are characterized into unimodal, bimodal and multimodal structures. When the pore throat structure of the sandy conglomerate reservoirs of the Cretaceous Guyang Formation in the western margin of the Hetao Basin includes more microthroats, it is more homogeneous, resulting in a poorer reservoir quality. The fundamental reason for the development of the modal pore throat structure is the mixed deposition of grain sizes, and the modal pore throat structure is controlled by the combination of macrothroats, mesothroats and microthroats.