Physical property of tight sandstone reservoir and its controlling factors:A case study of the fourth member of Cretaceous Quantou formation in Da'an area of Songliao basin

SUN Yu; YU Haitao; MA Shizhong; DENG Ming; XIANG Yao; ZHANG Yan

Abstract：Based on the analysis including physical property under overburden pressure,X-ray diffractions,rate-controlled mercury intrusion,casting thin section,scanning electron microscope analysis,this paper systematically studied the reservoir physical properties and the relationship between porosity and permeability under normal condition and overburden pressure,and analyzed the controlling factors of these physical properties.Research results show that the typical characteristic of tight sandstone reservoir is the existence of "sweet" reservoir with good physical properties under the general compact background.The varied types of sedimentary microfacies and pore structures are major controlling factors for the properties difference.Both the measurement results of porosity and permeability under normal condition and overburden pressure are in approximate linear distribution.Under overburden pressure,the loss ratio of porosity and permeability are about 5％ and 26％ respectively.While under normal conditions,values of porosity and permeability range from 1.1％ to 13.5％ and 0.01 to 16.00 mD.The porosity has a positive correlation with permeability,and the correlation curve has obvious segmentation features.Considering the densification origins of sandstone in different regions,the development degree of "sweet" reservoir and the complexity of geological conditions,it is suggested that the upper limit of the tight reservoir physical properties is that the conventional permeability value of 90％ samples is less than 1.00 mD,with the corresponding conventional porosity of about 12％.Meanwhile,the lower limit of the "sweet" reservoir physical property in the fourth member of the Cretaceous Quantou formation is that the conventional porosity value is 7.5 ％,and the conventional permeability is 0.2 mD.The different physical properties are integrated response of sedimentation and diagenesis.Strong compaction and multi-component cementation are major controlling factors of the sandstone densification.Different types of sedimentary microfacies and the heterogeneity of dissolution are primary influence factors for the physical property divergence.The pore structure is a key element that determines the permeability of the tight sandstone reservoir.