Fracture development and hydrocarbon accumulation in tight sandstone reservoirs of the Paleogene Huagang Formation in the central reversal tectonic belt of the Xihu Sag, East China Sea

By using thin section identification, cathodoluminescence, major and trace elements and fluid inclusion tests and authigenic illite dating, based on observation of core cracks, combined with the microscopic characteristics and imaging logging characteristics of fractures, the stages of the fractures in the Huagang Formation of the central reversal tectonic belt of the Xihu Sag in the East China Sea, and the matching relationship between the fracture development stages and the oil and gas charging stages are clarified. There are diagenetic fractures and tectonic fractures in the reservoirs of the Huagang Formation in the study area. The diagenetic fractures developed during the diagenetic stage of the reservoirs and have less effect on oil and gas migration and transport. The tectonic fractures are divided into three stages based on tectonic movements controlling the fractures and their relationships with hydrocarbon charging: The first stage of fractures was generated in the early stage of the Himalayan Movement–Longjing Movement(12–13 Ma ago), when the tectonic stress caused the sutures and shale strips to twist, deform, and break. Tectonic microfractures generated in this period had short extension, narrow width, and poor effectiveness, and had little effect on oil and gas migration and transport. The second stage of fractures came up during the middle-late period of Himalayan Movement–Longjing Movement(9–12 Ma ago), when tectonic movements caused the development of tectonic fractures in the central reversal tectonic belt, these fractures are of large scale, long extension, and good effectiveness, and matched with the first stage of large scale oil and gas charging(9–12 Ma ago), so they play an important role in oil and gas migration, transportation, and accumulation. The third stage of fractures were created from Himalayan Movement–Okinawa Trough movement to the present day(0–3 Ma ago), the fractures are tectonic ones developing successively;matching with the second stage(0–3 Ma ago) of large-scale oil and gas charging, they created conditions for continuous natural gas migration and transportation. All these prove that the development of reservoir fractures in the Huagang Formation of Xihu Sag can provide seepage space and continuous and effective channels for efficient migration and accumulation of oil and gas.

江苏地区句容凹陷油气充注史研究

江苏地区句容凹陷是中国南方海相中、古生界勘探较早的地区,油气显示丰富。根据有机包裹体的荧光颜色将容2井储层方解石脉中的有机包裹体分为不同的期次;用离线压碎的方法对容2和容3井储层方解石脉中有机包裹体的烃类组成进行了分析,并与储层中的轻质油进行了对比;结合句容地区的埋藏史对该区油气来源及充注史进行了探讨。结果表明:容2井和容3井油藏存在多期油气的充注;包裹体油代表了早期充注的油气,而不同的正构烷烃分布特征证明容2井早期充注的烃类经历了生物降解过程;早期充注的烃类主要来源于二叠系源岩,而现今三叠系储层中的轻质油为后期充注的,其主要来源于晚白垩世末二叠系及部分三叠系烃源岩的急剧沉降而生成的大量油气。

珠江口盆地阳江凹陷不同成藏期次原油成因及混源比例分析

阳江凹陷为珠江口盆地近两年来获得油气勘探重大突破的新区。采用饱和烃色谱—质谱实验、流体包裹体系统分析和全油气相色谱法混源油定量配比实验相结合,对阳江凹陷不同成藏期次原油成因进行系统分析,并对已获得混源油藏的混源比例进行了测算。阳江凹陷发生两期原油充注,充注时间分别为12.0~7.5 Ma和6.5~0 Ma。第一期原油来源于恩平20洼始新统文昌组文三段中浅湖相烃源岩,主要在中新统珠江组储层中聚集成藏;第二期原油来源于文一段和文二段中深湖相烃源岩,在中新统珠江组—韩江组储层中均有成藏。通过混源油定量配比实验建立混源比例测算模板,计算结果表明,B20-1、B20-2油田韩江组油藏均为第二期充注,B20-1油田珠江组油藏第一期和第二期充注量占比分别为39%和61%。关键成藏时期断裂活动强度、圈闭发育层段及有效烃源岩三者耦合关系共同控制着圈闭富集程度。

应用定量荧光技术判识番禺低隆起—白云凹陷北坡残余油藏并重构烃类充注史

珠江口盆地白云凹陷油气勘探程度较低，目前尚未发现油田，已发现的天然气田和含气构造主要分布在番禺低隆起-白云凹陷北坡，天然气藏多伴生一定数量的凝析油。应用储层砂岩颗粒萃取液荧光定量分析（QGF—E）技术，测定了9口探井224个天然气产层或非产层砂岩样品萃取物的荧光发射光谱及强度。依据测定结果，结合储层流体包裹体资料、测井资料、MDT资料以及埋藏史研究结果分析认为：研究区内残余油藏主要分布在珠海组和珠江组下段，且分布较广泛，油质较轻；20～10Ma期间区内可能发生过两期石油充注，14～0 Ma期间可能发生过两期天然气充注。