Controlling factors and physical property cutoffs of the tight reservoir in the Liuhe Basin

Tight gas sandstone reservoirs of the Lower Cretaceous Xiahuapidianzi Formation are the main exploration target in the Liuhe Basin in China. Petrology characteristics, reservoir space (pore space), controlling factors and physical property cutoffs of the tight sandstone reservoir in the Liuhe Basin were determined through the integrated analysis of several methods including: casting thin section, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR) and nitrogen gas adsorption (N2GA). The sandstones dominated by lithic arkoses and feldspathic litharenites are characterized by low porosity, low permeability and strong microscopic heterogeneity. The porosity has a range between 0.48% and 4.80%, with an average of 2.26%. Intercrystalline pores, intergranular pores, dissolved pores and microfractures can be observed through the casting thin section and FE-SEM images. Compaction and carbonate cementation are the two primary mechanisms resulting in the low porosity of the Liuhe sandstones. Microfractures improve the permeability of the tight sandstones and provide pathways for fluid migration and the storage of hydrocarbon accumulations. Moreover, the theoretical cutoff of the porosity in the Xiahuapidianzi Formation tight sandstones is 3.3%.