Experimental Research on Porosity of Ordovician Fengfeng Formation of Lu'an Coalfield, China

WANG Chang-shen; BAI Hai-bo; MIAO Xie-xing

doi:10.3321/j.issn:1000-1964.2009.04.001

Abstract：Due to the continuing coal excavation of Taiyuan Formation, North China permo-carboniferous coalfield, the evolutionary and engineering features of deep-buried Fengfeng strata have become an interesting and valuable subject for research. Samples taken from Zhang-54, a complementary exploitation borehole of Zhangcun Mine, Lu' an Coalfield, China, were ob-served and measured with thin-section identification, WdXRF, and mercury porosimetry tech-niques to determine the porosity and lithological features of the Fengfeng Formation. Results show that the upper part of the Fengfeng formation is mainly composed of fine-grained cystal-line limestone and the lower part of alternate layers of gypsum and dolomite. The pore types of the upper formation consist chiefly of intercrystalline pores, dissolved pores and stylolites, which are partially filled by clay, calcite, and gypsum. The average porosity of the upper Fengfeng is 1.15%, volumetric median pore diameter 0. 028 8 μm, area median diameter 0. 009 8 μm, and maximum throat-pore diameter 0. 02-0.04 μm. The pore volume of tiny and super-tiny pores accounts for more than 70% of the total pore volume. Aquifuges exist in, both the upper and lower parts of the formation, and an aquitard exists in the middle part of the for-mation. The thickness of the upper aquifuge that can serve as key-aquifuge is 142 m. The stud-y offers experimental support to the development of key-aquifuge theory and practice.