| Nice indication of oil and gas at Changxin and Feixianguan Formation of Yuanba 2 well has been discovered in Yuan ba gas field,which confirms reef flat reservoir existence in Yuan ba gas field.The marine facies layer in Feixianguan Formation pocessed great exploration prospect of gas.Therefore, we carry out detailed reservoir studies and accurately grasp the distribution law of reservoir extensions and scientifically assess the reservoir quality groundwater will contribute to the next exploration and development of research area.Based on the previous studies, this paper take full advantage of available data, involving geological data, well logging, testing of well and so on, to carry out detailed reservoir studies. This paper has researched into the deposition pattern analysis of Feixianguan Formation in lower Triassic, study of sequence stratigraphy, study of sedimentary characteristics, study of reservoir characteristics and reservoir's control factor and study of evaluation of reservoir. Through the study, We can realize that: (1)the sedimentary framework of the Feixianguan Foramation inherit the characteristics of Changxin Formation which is decided by"platform- slope- basin",but the"basin"has transformed to"shelf".The platforms is rimmed during the 1st and 2nd section of the Feixianguan Formation, After early Feixianguan 3 member, this paleogeographic framework is nearly filling and leveling, then the region of interest evolve to platform. (2) The Feixianguan Formation is divided into 2 3rd-order sequences, 11~16 4th-order sequences, and 20~31 5th-order sequences, 3rd-order is divided into11 4th-order sequences and 205th-order sequences。The 3rd-order sequences can be divided into 11 4th-order sequences, and 20 5th-order sequences when it doesn't include LST, the number adds when it include LST.LST mainly develops in slope and shelf,the upper part of the slope and platform margin only includes TST and HST. Furthermore, the frameworks of the 3rd-order sequence and the high-frequency sequence are built for the study area.(3) In the framework of the sequence stratigraphy, by analyzing the sedimentary facies vertically and ichnographically, it shows that the shoals not only occur mainly in the upper HST of the lower sequence in the platform margin and in the TST of the upper sequence,but also occur in the middle and lowerHST of the upper sequence. the evolution of platform edge shallow facies is progradation, and is aggradation when the shoals occur in the interior of the platform. (4)Observing from core and core wafer, we recognize that the main reservoir rock is oosparite and calcarenyte, and the main reservoir pore space is intragranular emposieu and moldic pore, and the secondly reservoir pore space is intergranular pore.the pore configuration of the reservoir is bad, and most pores in the the reservoir are micropores. (5)The main diagenesis have compaction, pressolution, cementation, denudation, dolomitization, rejuvenation of crystals, and cataclasis,and so on. the dissolution which happened during the syngenesis influenced greatly on the formation and quality of the reservoir. The dissolution happened during the burial react greatly on the melioration of the dimensions and quality of the reservoir. cataclasis promotes the quality of the permeability(6) Reservoir occurs mainly in the platform margin, the evolution of the reservoir develop in platform margin is progradation, and is aggradation when the reservoir develop in the interior of the platform. And the reservoir forming is also controled by kinds of diagenesis and tectogenesis.(7) The core porosity of the reservoir is between 1%～2% , 70.5% of the porosity less than 6%, permeability of the reservoir is between0.01～1mD. porosity is smaller than 6%,and most of it is between 2%～3%.Communication of pore and correlation between porosity and permeability is bad,then,a conclusion can be made that the reservoir of the Feixianguan Formation falls into three category.
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