The Microfacies Combination and Character istics of Delta Front in Yanchang Formation (Triassic) of Jiyuan Area Shaanxi-Gansu-Ningxia Basin

Key words: 
• delta /
• microfacies combination /
• mesa delta front and sloping delta front /
• Shaanxi-Gansu-Ningxia basin /
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Abstract: A series of gentle slope delta are developed in Yanchang Formation in Jiyuan Area of Shaanxi-Gansu-Ningxia Basin. The delta front in this area can be divided into mesa delta front and slop ing delta front. The deposition models of delta along gentle slop are proposed based on the strength of the current in distributary channel and the depth of water in the lake. According to the research of underwater distributary channel, recombination bars and mouth bar, we can establish the assorted scheme and discriminating characteristics. For example, the distributary channels are composed of truncated underwater distributary channels and underwater superposition channels. The rivermouth bars are composed of the integrated mouth bars and recombination bars. The recombination bars consist of mouse bars at the bottom and underwater distributary channels at the top, and it can be subdivide into up side deformity recombination bars, integral recombination bars and downside recombination bars. This type of compartmentation scheme can be helpful to identify and distributing prognosticate of high quality reservoir, and it can also serve to subdivide the flow unit in oil exploitation.