摘要:
鄂尔多斯盆地位于华北地台西部 ,中奥陶统马家沟组含硬石膏的白云岩是盆地中主要的储层与产层之一。奥陶纪由于西侧贺兰裂谷再次开启 ,裂谷肩部发生抬升 ,以及南侧逆冲断层的左行走滑作用 ,在盆地西部和南部形成一“L”形隆起 ,又称中央隆起。在隆起东侧由均衡补偿作用伴生一西缓东陡的边侧坳陷 (盆地 ) ,称 (内 )陆棚盆地亚环境。通过沉积相研究 ,建立了两个马家沟组的沉积模式。其一为东西向穿越 (内 )陆棚盆地中心的陆棚沉积模式 ,该模式中的 (内 )陆棚盆地与中央隆起之间为水下凸起—洼地亚环境 ,其东为开阔内陆棚亚环境。马一时、马三时、马五时(内 )陆棚盆地发育为含白云岩的硬石膏岩 ,石盐岩盆地 ,盆缘主要发育白云岩—硬石膏岩坪 ,马五时西缘硬石膏岩—白云岩坪发育 ,是天然气藏主要分布区。以上表明沉积时气候干热 ,海平面下降 ,具深坳陷海水浓缩成盐特征。马二时、马四时气候湿热 ,海平面上升 ,(内 )陆棚盆地发育成石灰岩白云岩盆地 ,周围盆缘发育为 (含 )白云岩—石灰岩坪。水下凸起—洼地亚环境于马三时和马五时发育白云岩 ;马四时发育石灰岩 ,南延则过渡为白云岩、石灰岩的浅滩。东侧的开阔内陆棚亚环境 ,主要发育微晶—亮晶颗粒石灰岩、白云岩夹硬石膏岩、风暴岩。马六时 ,中央隆起以东根
Abstract:
Ordos basin is located in the west of north china platform, middle Ordovician Majiagou formation is one of most important nature gas reservoirs. In Ordovician the overspread of the southern Helan rift and left strike slipping of the southern overthrust led to rift shoulders being warped and rise in the west and south of Ordos basin, and “L” sharp uplift or names of center uplift was formed. At the same time, as a result of equilibrium activity, in the east of the basin formed an unsymmetrical compensation basin (depression), which is named inner shelf basin. Two different sedimentary models are presented, one is sedimentary model of shelf and another is sedimentary model of distally steeped ramp. The sedimentary model of shelf is extend from east to west and pass through the center of inner shelf basin, which runs through main natural gas reservoirs area of Majiagou formation. The east part of three sub environments, that's to say, inter uplift lecuna and under-water uplift, inner shelf basin, open inner shelf, the latter most located out of the research area. In Majiagou 1,3,5 members depositional stage, the climate was dry and sea level was fall by the evaporation, the L-sharp uplift was close to the sea level or above it, or became the erodedarea, the inner shelf basin became semi-restricted or restricted environment. In the center of the basin deposited anhydrock, halilith and some dolostone compounds, in the basin marginal flat was deposited dolostone interbeded with anhydrock. In 2,4 stages, the climate was moist and sea level raised, the inner shelf basin became dolostone limestone-deposited limestone or dolo-limestone. In Majiagou 6 stage, because most of stratigraphy few wells, there's limestone shelf sedimentary environment. The west shelf lies on the L-sharp uplift, in all of the Majiagou stage was deposited limestone or dolostone. The steep slop, along Helan rift margin, developed carbonate gravity flow stones. However, in submarine through developed turbidites mixed with carbonate and silicon debris. The distally steepened ramp developed in all of Ordovician lies on the south of L-sharp uplift, that's to say, present Weibei uplift area. In 1,3,5 members depositional stage, there is dolstone distally steepened ramp. However, in members 2, 4, 6 present dolostone-limestone distally steepened ramp. According to the sedimentary model, in this paper present lithofaices paleography map from 1 to 6 member of Majiagou formation.
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