Physical property and origin of lowly permeable sandstone reservoir in Chang 2 division, Zhang-Han oilfield, Ordos Basin

• Published in: Energy exploration & exploitation Vol. 27; no. 5; pp. 367 - 389
• Main Authors: Gao, Chao, Wang, Zhenliang, Deng, Jie, Zhao, Jinghui, Yang, Xianchao
• Format: Journal Article
• Language: English
• Published: London, England Multi-Science Publishing Co. Ltd 01.10.2009; SAGE Publications; Multi-Science
• Subjects: Applied sciences; Carbonates; Cementation; Cements; Crude oil, natural gas and petroleum products; Diagenetic processes; Energy; Exact sciences and technology; Feldspars; Fuels; Geological facies; Geology and geochemistry. Geological and geochemical prospecting. Petroliferous series; Man made reservoirs; Porosity; Prospecting and exploration; Prospecting and production of crude oil, natural gas, oil shales and tar sands; Quartz; Sandstones; Asia; China; Diagenetic facies; Ordos Basin; Pore media; Lowly permeable sandstone reservoir; Zhang-Han oilfield; Case study; Scanning electron microscopy; Diagenesis; Petroleum geology; Oil field; Permeability; Porosity; Experimental study; Physical properties; Deposition; Sandstone
• ISSN: 0144-5987; 2048-4054
• DOI: 10.1260/0144-5987.27.5.367

Lowly permeable sandstone reservoirs play an important role in the exploration and exploitation of natural gas and petroleum in China. The reservoirs are major lowly permeable sandstone reservoirs in Chang 2 division, Yanchang Formation, Upper Triassic in Zhang-Han oilfield, which located in the northern Shaanxi slope of Ordos Basin. According to the distribution and composition of sand beds, integrated measured physical properties, micro-pore structure analysis, cast thin section observation, scanning electron microscopy, the impacts of deposition and diagenesis on porosity evolution are analyzed. The essential diagenesis causing the porosity loss is evaluated quantitatively, and finally the origin mechanisms of low permeability reservoir in Zhang-Han oilfield are discussed. The results show: (1) Fine particle and low compositional maturity arkose are the material foundation of the formation of poor physical property sandstone; (2) The main pore space of reservoir is secondary pores. There are two types of combined pores that including dissolve-residual pores and dissolve-micropores. The porosity values display an approximately normal distribution, and permeability values are asymmetric distribution of the logarithm in lowly permeable sandstones. Their correlation coefficient becomes more and more worse with the decrease of permeability; (3) There are four diagenetic facies, in which three diagenetic facies belong to extra-lowly permeable and ultra-lowly permeable reservoir sandstones and widely distributed, and they are diagenetic lithofacie background of lowly permeability sandstone; (4) In low compositional maturity arkose, its initial porosity is 1/4 lower than conventional reservoir, the secondary and dissolved pores are main pore types of lowly permeable reservoir rocks. It is also a key factor of effective oil-bearing of lowly permeability sandstone.