Description On Geologic Characteristics Of Lower Cretaceou Quantou Formation Gas Reservoir Of Shuang Tuo Zi Gas Field

Shuang Tuo Zi structure is located in the south of Hua Zi Jing terrace in the central depression of Songliao basin. The structure, showing entirely a nosing structure cut by north-south faults, is located in the favorable area of oil-gas migration and accumulation, and has superior condition of petroleum geology. Few gas producing formations were discovered through the exploration of Shuang Tuo Zi structure, and Quantou formation was an important gas producing formation as well as the main aimed formation of the research.Quantou formation was divided into four sections based on lithologic character. Quan 1 section was developed when the fault depression deposition in Songliao basin transformed into depression deposition, and Quan 2 section to Quan 4 section were developed during the period of depression deposition. Among those sections, Quan 1 and Quan 3 were main gas producing formations. As formations of terrestrial clastic rock, facies change of Quan 1 and Quan 3 section in horizontal or vertical direction is more frequent. Reservoir developed chiefly in sand body while the distribution of sand body was in control of the distribution of sedimentary facies. Based on the cognition to the structural evolution and the depositional setting, the data of core,logging and well logging were used to identify and classify sedimentary facies of Quan 1 and Quan 3 section, then the distributing maps of sedimentary facies ofⅨsand set in Quan 3 section,Ⅲsand set,Ⅵsand set andⅦsand set in Quan 1 section were drawed up, and finally, the sedimentary facies models of this area were summarized. Study shows that the upper Quan 1 section((Ⅰ～Ⅴsand set) and Quan 3 section developed the meandering river deposition system, and the lower Quan 1 section(Ⅵ～Ⅷsand set) developed the braided river deposition system. The meandering river sedimentary facies could be further divided into five sorts of sedimentary microfacies: marginal bank,levee,crevasse splay,channel lag and bet lands. and sand body of marginal bank was developed mostly. Similarly, the braided river sedimentary facies could be further divided into four sorts of sedimentary microfacies: piont bat, crevasse splay, channel lag and bet lands, and sand body of piont bat was developed mostly.According to the analysis of the result of statistics of core physical properties data, the reservoir could be divided into four types and the electrical identification standards of various types of reservoir were built up. Quan 1 section chiefly developed the reservoir of middle-low porosity and middle-low penetration, and Quan 3 section chiefly developed the reservoir of middle-high porosity and middle penetration .Though the synthetical analysis of sedimentary microfacies and the data of core physical properties, it was thought that the physical properties of marginal bank reservoir is the best, which followed by piont bat, crevasse splay, channel lag and levee. The research on casting thin slice and the data of mercury penetration shows that the reservoir of Quantou formation mainly developed four types of pore, that is, the residual protozonal intergranular pore, the corrosional intergranular pore, the intergranular miniature pore and the intragranular corrosional pore, and the communication of pore throat is well. Finally, the evaluation of intraformational aeolotropism and interformational aeolotropism of the reservoir shows that the intraformational aeolotropism of levee sand body is the weakest, then piont bat , marginal bank and channel lag, and finally crevasse splay. The interformational aeolotropism of the reservoir of Quan 3 section is weaker than the reservoir of Quan 1 section.Through the research in depth on structure, sedimentary facies and characteristics of reservoir of Quan 1 section and Quan 3 section, the important foundation to the next exploration and exploitation of gas reservoir is provided.