【作者】 邓秀芹；

【导师】 李文厚； 赵文智；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2011， 博士

【摘要】 鄂尔多斯盆地延长组发育低孔渗大型岩性油藏。近几年,油气勘探获得了重大突破,发现了西峰、姬塬、华庆大油田及塔儿湾、合水含油富集区。目前已形成了东北、西南、西北和湖盆中部4大富油区的石油分布格局。其中湖盆中部以发育大型超低渗透油藏为主,已发现多个探明地质储量超过亿吨的含油区块。超低渗透大型岩性油藏成藏条件复杂,研究难度大。开展超低渗油藏成藏机理研究可为鄂尔多斯盆地的进一步增储上产、勘探开发决策提供科学依据,同时对类似盆地油气发现与生产具有重要的借鉴意义。本次研究重点分析大型超低渗透岩性油藏的沉积类型、储层成岩致密史、输导体系类型及特征、油气运聚动力及规律,探讨超低渗透油藏形成的主控因素,总结成藏规律。主要在以下几个方面取得了新的认识：提出早印支运动控制了晚三叠世沉积演化,多幕构造控制了盆地多旋回充填特征。利用磷灰石裂变径迹、锆石U—Pb微区测年等综合分析技术,通过对盆地周缘岩浆岩体和盆地腹部延长组凝灰岩年代测试,识别了印支运动构造期次,明确了受西秦岭造山运动的影响,长8末存在一次显著的构造事件,该事件导致盆地格局、沉积演化和生物面貌等方面发生重大变革。构建了湖盆中部延长组厚层砂体沉积模式。长6、长7油层组厚层深水砂岩主要由深水三角洲、砂质碎屑流、滑塌、浊积岩等沉积类型组合形成,为大型三角洲—重力流复合储集体。重力流砂体复合连片,平行于相带界线带状展布,深水三角洲砂体主要分布在白豹及其北部地区,呈带状或朵状分布。恢复了生排烃高峰期储层物性。明确了石英加大边中的烃类包裹体代表了生排烃高峰期石油充注。以该认识为基础,探讨了生排烃高峰期古物性恢复方法,计算主成藏期长6—长8储层孔隙度平均12%-20%,渗透率可达到10×10-3μm2以上。提出含铁碳酸盐胶结是造成储层致密化的最终决定因素,生排烃高峰期储层尚未致密化。探讨了不同类型的输导体在石油运移中的作用。主成藏期,连通的、尚未致密化的砂体是油气运移的主要通道,有油气运移痕迹的、强烈充填的北北东向裂缝和弱充填的近东西向裂缝形成于喜山期和燕山末期,它们沟通了延长组上部和侏罗系储层与长7优质烃源岩,侏罗系古河为延长组上部和延安组石油成藏提供了运移通道。划分了延长组成藏动力系统,明确了不同子系统中流体运移特征。延长组中下部整体为超压流体动力系统。根据岩性、物性和过剩压力特征,进一步划分了西南和东北2个动力子系统。陇东子系统以纵向运移为主,纵向过剩压差低值区为成藏有利区,陕北子系统既有纵向运移,又有横向运移,横向过剩压力低值区为成藏有利区。建立了鄂尔多斯盆地中生界的成藏序列。延长组成藏序列为“延长组成藏序列为“烃源岩上覆浮力、超压驱动型油藏→烃源岩下伏超压驱动型油藏→长3以上裂缝沟通、古河输导型油藏”的成藏序列。可划分早期浮力、超压驱动充注,后期裂缝调整的两个成藏阶段。总结了延长组石油富集规律。优质烃源岩的范围控制了低孔渗大型岩性油藏的分布；湖盆中部三角洲前缘和重力流砂体为超低渗透油藏发育的主要相带；三角洲前缘存在相对高渗区,为有利的成岩相带；过剩压力(压差)低值区为延长组中下部油气运移聚集的有利地区；前侏罗纪古地貌控制了延长组上部和侏罗系油藏的分布。更多还原

【Abstract】 Large oil reserviors with low permeability are well developed in Ordos basin. Oil exploration and major breakthroughs have been achieved. Large oil pools, such as Xifeng, Jiyuan and Huaqing oil pools and some oil riched regions as Taerwan and Heshui have been found in the last ten years. So far, four large-scale hydrocarbon riched accumulations have taken shape, located in the northeast, the southwest, the northwest and the depocenter in Ordos basin respectively. The physical property of large-sized lithogical reservior is poor in the depositional center. It belongs to ultra-low permeability reservior. Some oil-riched area with submited proved-geological-oil-reserves exceeding 100 millions tons, have been discovered. Complex accumulation process makes it difficult to study. The research of accumulation machanism on ultra-low-permeability reserviors in the depositional center of Ordos basin will provide scientific basis for production and reserve increasing in the basin, and will perform enlightenment for similar investigation in other hydrocarbon riched bearing basins in future. Aiming at exploring the key parameters of reservior and sumerizing hydrocarbon migration and accumulation rules, this research emphasizes on the sedimental type, diagenesis and densification of reservior, hydrocarbon transporting systems and petroleum migration and accumulation dynamic. Some new views are promoted as follow:It is presented that early Indosinian movement dominant the evolution of Ordos basin and the characteristics of multi-cycle sedimentary evolution is the consequence of polycyclic tectonic movement. The tectonic epochs is identified on the base of comprehensive analysis of apatite fission track and a LA-ICP-MS U-Pb chronological study of zircons, sampled from magmatic rock around the basin and the tuff rock at the bottom of chang7 member in Yanchang formation in the basin. A new option is advanced that affacted by west Qingling orogenesis, a intense tectonic event happened at the end of sedimental phase of Chang8 strata. It made graet change on basin framwork, depositional feature and biological character.New modle of thick deep-water sandstone is built. Stretching along the facies lines in depositional centre of Ordos basin, the thick deep-water sandstone of Chang6 and Chang7 oil bearing formation consists of deep-water delta, debrite, slide and turbidite, and can be named as large delta-gravity complex. The compound sandbody, origining from gravity-flow, parallels the faces borderlines, and deep-water delta sandbody takes on the shape of lobe and belt, distributing at Baibao and its northern areas.The reservior porosity at premium stage of hydrocarbon generation is uncovered. It is suggested that hydrocarbon inclusions cathched in quartz overgrowths stand for the oil injection occurred at premium stage of hydrocarbon generation and expulsion. Probing into the computational method of reservior porosity at premium stage of hydrocarbon generation and expulsion, it shows that the average porosity of Chang6-Chang8 was mainly arranged from 12%to 20%, and the permeability should exceed 10x10-3μm2 at the stage. Ironed carbonate cement made the reservior compacted eventually and the sandstone peroperty at that time was raletively better than that at present.The role of different transporting passages in oil migeration is argued. Interconnected and uncompletely densified sandbodies palyed as the main passages for migration and accumulation at the phase of oil-pools forming. Fractures and joints with calcium intense filling, which extend along the direction of NNE-SSW, were formed at the Himalayan period or at the end of Yanshanian period. Some of them remain the trail of petroleum transit. They connected the premium oil source of Chang7 member and the reserviors of upper Yanchang formation or Yan’an formation. Early Jurrasic river channel did as one of the important transport passage for oil accumulation at upper Yanchang formation and Yan’an formation.The hydrocarbon dynamic system is divided and fluid migeration feature in different systems and sub-systems is discussed. Middle and lower Yanchang formation was a excess pressure hydrodynamic system during the deepes-depth period. According to lithology, property and overpressure, it can be divided into two subsystems, i.e. the southwest dynamic subsystem and the northeast dynamic subsystem. As to the southwest hydrodynamic subsystem, the higher the altitude, the more seriously compacted the reservoir is. Vertical hydrocarbon migeration played a dominant role during the process of pool forming. The areas with low overpressure-difference or the areas with relative low overpressure-difference in high overpressure-difference region are the preferential places for oil migeration. As to the northeast hydrodynamic subsystem, oil migerated not only vertically but also transversely through the layered carrier bed. The areas with low overpressure are the faverable places for oil accumulation in the northeast dynamic subsystem.Accumulation sequence of Mesozoic Yanchang formation and Yan’an formation in Ordos basin is set up. The sequence is:①reserviors above the source rock, drivern by buoyancy and excess pressure;②eserviors underneath the source rock, drivern by excess pressure;③eservior of Chang3 and its upper strata, connected by fractures and joints and oil tranporting in Jurrasic river channels. The enrichment regularity of petroleum in Yanchang formation is summarized. It is shown that the delta-front and gravity-flow sediment are the main areas for the ultra-low-permeability reserviors. The raletive higher permeability reserviors located in the delta front and it domimants the distribution of oil-riched area and high yield area:the places with relative low overpressure or relative low overpressure-difference are the preferential places for oil migeration and accumulation at the middle and low part of Yanchang formation. Pre-Jurrassic palaeo-geomorphology controls the reservior distribution of upper Yanchang formation and Jurrassic.更多还原