天窗型古潜山油气藏形成与盆地深部水动力循环

【作者】 刘静江；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2010， 博士

【摘要】 轮南古潜山油气藏是塔里木盆地的一个大型碳酸盐岩古潜山油气藏,潜山相对高差2000m,面积20000km2,埋深4100m。潜山主要储集空间为奥陶系碳酸盐岩风化壳岩溶裂缝～溶洞系统；潜山周围斜坡由巨厚的上奥陶统泥岩、石炭系泥岩构成披覆盖层,但在潜山顶部有一个80km2的区域为巨厚的三叠系含水砂岩所覆盖,形成古潜山的“天窗”区。由于天窗的存在从而形成了一种新类型的油气藏——天窗型古潜山油气藏。天窗型古潜山油气藏油气主要分布在潜山斜坡部位,而潜山的高部位为水区或含油水区；天窗型古潜山油气藏油水界面是倾斜的,油气藏具有水动力特征。控制油气藏形成的主要因素是储集层、差异溶解作用和水动力作用。储集层控制油气沿潜山表层风化壳聚集；差异聚集作用控制油气平面上差异分布及局部高点中的聚集；水动力作用抑制油气的散失,控制油气沿潜山斜坡聚集,并控制油气藏的形态特征。虽然“天窗”的存在不利于油气的保存,但由于逆向水动力的作用,在油气运移的上倾方向上形成了水动力遮挡,使后期充注的油气得以保存,同时也阻止了早期聚集的油气继续逸散,这也可能是轮南古潜山历经劫难仍能够富集油气的主要原因。在具有多期成藏历史的油气藏中,后期新来的油气会在老的油藏里发生溶解,新来油气的聚集是以溶解方式进行的。差异溶解观点揭示了叠合盆地普遍存在的一种常见而又常常被忽视的油气聚集现象,即地层条件下油气的相互溶解。差异溶解作用的实质是油气分子之间的溶解不平衡,其表现形式为新生成的油气在原有油藏里边溶解边聚集。差异溶解作用的结果是造成新老油气的差异性混合,使油藏中原有油气的物理性质、地球化学特征发生不均匀变化,从而造成油气分布的复杂而有规律的变化。塔里木盆地深部存在着广泛的流体流动,这种流动以浅表层流体循环和深层流体循环形式存在。浅表层流体循环的动力为流体自身重力,深层流体循环的主要动力是盆地深部大地热流分布的差异造成的局部地热异常。盆地水动力结构随大地构造演化而演化,不同水文地质阶段、不同的水文地质结构层次,对于盆地流体流动具有不同的驱动类型。盆地流体循环为盆地深部的物质传输和能量传递提供了必要的载体,为深部油气和其他各类矿床的形成提供了必要的储集空间和成藏动力。更多还原

【Abstract】 Lunnan buried hill reservoir is a super carbonate reservoir with 2000m high and 20000km2 area and 4100m depth buried under the ground, Tarim basin. The main reservoir space of the reservoir is Ordovician carbonate ancient weathered crust Karst cave-fractures system. Above the hill, there was a giant thick Ordovician or Carboniferous mudstone onlapped on the slopes of the hill as a capping formation, but a more than 80km2 area in the top of the hill covering with a thick Triassic water-bearing sandstone came into being a top-window area for the hill. It is just because of the top window so that a NEW type of reservoir formed, which called Top-opening Buried Hill Reservoir. In this type of reservoir, the oil and gas accumulated mostly in the slopes surrounding the hill. The upper area near the top of the hill was filled with water or water and little oil. The oil-water interface in such a reservoir was tilting, and the oil-gas accumulating has a unique hydrodynamic features. The genesis of the Lunnan super buried hill reservoir would have likely related with the hydrodynamism due to the Top-window. The main factors dominated the reservoir forming were reservoir, differential dissolution and hydrodynamism. The reservoir controlled the oil and gas accumulating in the surface weathered crust of the buried hill, differential dissolution controlled the oil and gas differential distributing in the hill and the hydrodynamism restrained the oil and gas leaking from the hill and controlled it accumulating in the slope of the hill and controlled the shape of the oil and gas reservoir.Although the top window was unfavorable to the oil and gas preserving, the inverted water dynamic created a sealed zone at the upper of the slope and prevented the oil and gas escaping through the window, which would be the essential reason that the buried hill richly accumulated oil and gas in despite of broken once and again.The hypostasis of differential dissolution is the molecules of oil and gas dissolving and diffusing each other. The differential dissolution made oil and gas mixing and complicated distributing in the reservoir, but in a certain rule:the traps close to the source would be full filled with dry gas or condensate gas, and far away from the source would be oil.There were broad fluids flow in the deep of Tarim Basin, and the flows were shown as the shallow fluid circulation and deep hydrothermal circulation. The driving force driven the deep hydrothermal circulation is the local geothermal discrepancy coming from the difference of thermal flux distributing in the deep of the basin. The hydrodynamic texture would be changed followed the tectonic framework changing, and there would be different driving mechanism at a different hydrogeologic stage and a different hydrogeologic frameworks for the basin fluids. The basin fluids circulation flow supplies vital carriers for matter transport and energy convection, and provides necessary spaces and dynamic for oil, gas and other ores accumulating.更多还原