Study On The Sedimentary System Of Member 2 And Member 3 Of Lower Permian Xiashihezi Formation In Daniudi Gas Field

The sandstone of the member 2 and member 3 of lower Shihezi formation of lower Permian is the important reservoir in Daniudi gas field, Ordos basin. In order to know reservoir more distinct, the study on gas enrichment law has important theoretical and realistic meaning. With the foundation of detailed sedimentary study, careful analyses have been studied on the sedimentary system of the member 2 and member 3 of lower Shihezi formation of Daniudi gasfield, such as depositional feature, microfacies analysis, sand body distribution, depositional model and sedimentary evolvement. Study results offer theory and tech support for exploration and the production of the gas field.Mainly by means of taking the observation and description of core, and comprehensive study of logging, well study, survey and paleontology data, with the exercitation of sedimentology theory, enriched the intrinsic sedimentary viewpoint that the lower Shihezi formation of Daniudi gasfiled merely generally develops fluvial facies. This research considered that braided delta and shallow-lake sedimentary system developed in the lower Shihezi formation.This paper defines the tempestites of the member 2 and member 3 of lower Shihezi formation of lower Permian in the Daniudi gas field. The former viewpoint is that the fluvial sedimentary system develops in this work area, however, the discovery of tempestites proves that the lacustrine facies also develops in the work area. During the member 2 and member 3 of lower Shihezi formation of lower Permian, the geological backgrounds, which are broad lake, gentle terrain and shallow water, benefit the developing of tempestites. On the basis of core observation, grain analysis and the other data, the work area develops abundant tempestites, and the main types of tempestite sedimentary characteristics have been identified, including truncated structure, gutter cast, hummocky cross-stratification and scouring surface. The cumulative probability plots and sedimentary structures reflect that the transportation medium has characters of tractive current and gravity flow synchronously. The perfect vertical sequence of the tempestites in the work area is a Bouma-like sequences, which are A-graded and massive bedding segment, B-parallel bedding segment, C-hummocky cross stratification segment, D-Ripple bedding segment, E-mudstone segment. The tempestites is a typical evidence of lacustrine facies, therefore, the tempestites take a new sedimentary facies type in the work area and have a significance of reconstructing the palaeogeography.With lacustrine sedimentary viewpoint and depositional model, using gas reservoir distribution model in Daniudi gasfieil, this paper firstly realized that the gas reservoir distribution was obviously controlled by lake-coastline. The source rock, sandbody, reservoir distribution and migration of gas are influenced by lake-coastline.