苏干湖盆地及毗邻柴北缘西段侏罗系残留地层发育特征

前期的油气勘探和评价揭示了柴北缘西段侏罗系具有良好的油气和煤炭勘探前景。在前人研究的基础上,利用野外露头、岩心、钻井及地震等资料,对柴北缘西段侏罗系残留地层发育特征进行了系统研究,初步落实了侏罗系残留地层的分布。侏罗系自下而上可划分为下统的湖西山组和小煤沟组,中统的大煤沟组及上统的采石岭组和红水沟组。下统主要见于冷湖构造带(湖西山组)和苏干湖盆地东部的向阳煤矿(小煤沟组)。湖西山组的下部岩性为厚层粗粒沉积物,表现为水下扇沉积特征,上部为大套湖相暗色泥岩;小煤沟组厚度较薄,沉积物粒度粗,发育煤层。中、上侏罗统主要分布于赛什腾凹陷和苏干湖盆地内的西部凹陷、中部凹陷、向阳煤矿。根据钻井显示,苏干湖盆地内中侏罗统主要发育大煤沟组五至七段,岩性主要为灰色、灰黑色泥岩夹灰色细砂岩、砾岩及薄煤层;其中五段为主力煤层和油气烃源岩层。上侏罗统岩性主要为棕红色、褐色泥岩夹砾岩、砂岩。残留地层的分布主要受控于沉积中心的迁移和断裂的展布。

THE DEVELOPMENT CHARACTERISTICS OF THE RESIDUAL JURASSIC STRATUM IN SUGANHU BASIN AND THE WEST SECTION OF THE NORTHERN MARGIN OF THE QAIDAM BASIN

Previous exploration and assessment of oil and gas showed that Jurassic stratum in the west section of the northern margin of the Qaidam Basinare are of excellent potential in oil and gas and coal. Based on the previous research, development characteristics of the residual Jurassic stratum in the west section of the northern margin of the Qaidam Basin are studied systemically through field outcrops, cores, drilling and seismic data, and the distribution characteristics are determined preliminarily. Jurassic could be divided into several formations from bottom to top, including Huxishan and Xiaomeigou formation in the lower part, Dameigou formation in the middle part, and Caishiling and Hongshuigou formation in the upper part. The Lower Jurassic mainly distributes in Lenghu structural belt(Huxishan formation)in the Southern Suganhu Basin, and Xiangyang coal mine in the eastern Suganhu basin(Xiaomeigou formation). The lithology of lower Huxishan Formation consists of thick coarse sediments which show features of subaqueous fan sedimentation, and the thick dark shales develop in the upper formation; Xiaomeigou Formation is thinner with coarser sediments which are suitable for the development of coalbed. The Middle and Upper Jurassic stratum mainly developped in the Saishiteng sag and the West Depression, Central Depression and Xiangyang coal mine inside the Suganhu Basin. According to the drilling data, it is mainly the fifth to seventh member of Dameigou formation that developed inside Suganhu Basin, with lithology of grey, ash black shale interbedded with fine sandstone, conglomerate and thin coal layer, and the fifth member is predominant coalbeds and oil and gas hydrocarbon source rocks. The lithology of Upper Jurassic is brownish red shale interbedded with conglomerate and sandstone. The distribution of residual stratum is basically controlled by the transfer of the deposit center and the distribution of the fractures.