Abstract:

The Well YNS is located in the Yidikelike structural belt in the eastern Kuda Depression. The Yangxia Formation develops sandstone and conglomerate of braided river delta，while the Ahe Formation develops thick lacustrine mudstone with the interlaver of sandstone and coal seam.  Based on the thin section observation and physical property test of the sample，it is revealed that in the rock types of the Lower Jurassic reservoir, the litharenite is predominant with relatively more detritus of igneous rock. The ferruginous and argillaceous cements are dominated in the Yangxia Formation，while the siliceous and calcareous cements are the major cements in the Ahe Formation.  The porosity of the Lower Jurassic reservoir is smaller than 12%，mostly between 2%  and 8%，the permeability is largely between0.1 x 10^-3μm² and 5.0x 10^-3μm²，and the average pore throat radius varies from0.2 -3μm to 0.6 -3μm.Generally，the reservoir physical properties of the Ahe Formation are better than those of the Yangxia Formation. The porosity and permeability of Yangxia Formation and Ahe Formation both display characteristics of two sections varying to worse along the increasing depth，due to the compaction and original materials. There are superior intragranular pores and micropores in the Low er Jurassic reservoir owing to the dissolution of the soluble constituent such as feldspar and detritus.  Relatively，the reservoir of Ahe Formation develops more vuggy porosities because of its coarse grains and more feldspar and detritus.  The fractures by the tectonic stress play an important role to improve the reservoir physical properties.

Key words: control factor, tight reservoir, Lower Jurassic, Well YNS, Kuqa Depression