Abstract The Himalayan orogeny has shaped the sedimentary basins of the region, where continuous deformation formed both ‘conventional’ and ‘unconventional’ petroleum systems at multiple stratigraphic levels ranging in the age from Precambrian to Neogene. Himalaya is considered to be prospective for hydrocarbon exploration because of its suitable tectono-sedimentary environment, oil/gas shows, and the presence of commercial oil and gas discoveries in broadly similar structural settings in the eastern and western regions. Although detailed surface geological mapping, the acquisition of geological data and the drilling of wells has considerably improved the understanding of the geological and structural setting and the hydrocarbon potential of the NW Himalaya, commercial discoveries have remained largely elusive. In the NW Himalaya the Precambrian-Cambrian sequences that are of primary interest include the Salt Range Formation (Potwar Basin), and also some sequences in the Lesser-and-Sub-Himalaya, such as the Proterozoic Sirban Limestone Formation; in the Kashmir and Bhadarwah-Chamba basins further to the northeast, and in the Garhwal Group and the Krol belt in the southeast. The Palaeozoic sedimentary rocks exposed within the Lesser Himalaya and the Tethyan Himalaya (represented by the Kashmir, Zanskar-Spiti, Kinnaur-Uttarakhand and Kumaon basins) have been subjected to low grade metamorphism, and presently have no significant hydrocarbon generation potential. The Cambrian Khewra and the Permian Tobra formations form hydrocarbon bearing reservoirs in the East Potwar. The Palaeozoic stratigraphy of the Zanskar Tethyan Himalaya in northern India is rather similar to that of the Peshawar Basin in Pakistan. The thick argillaceous successions are the best potential hydrocarbon source rock horizons within the Palaeozoic. The Mesozoic and Early Eocene successions of the Tethyan Himalaya were deposited in the shallow southern margin of the Tethys Ocean. In the western Himalaya, the Tethyan Himalayan succession is exposed in Kashmir, Zanskar, Chamba and Spiti basins. The Mesozoic successions include thick sequences of organic material rich argillaceous sediments. The Triassic and Jurassic strata are generally poorly developed or absent in the eastern Potwar Basin, while they get thicker towards the west Potwar and Kohat basins. The sandstones of Jurassic age are proven reservoirs, and potential source rocks are present. The Mesozoic succession of the Kashmir Basin is represented by the formations of the Triassic age. Some of the shales contain organic matter (OM) and could represent viable hydrocarbon source rocks, while some of the limestones, dolomites and sandstones have sufficient reservoir characteristics. The OM content of the argillaceous sediments within the Mesozoic-Tertiary succession of the Zanskar-Spiti Basin (Ladakh Himalaya) is appropriate for hydrocarbon generation. The Cenozoic foreland basin of the Himalayan orogen was deformed by a southward migrating thrust system during the Late Miocene-Quaternary. The Sub-Himalaya Zone contains a sequence of Cenozoic sedimentary rocks divided into the Subathu and Dharamsala (=Murree) formations, and Siwalik Group. Hydrocarbon source rocks are present in the Subathu and Dharamsala formations; while the Lower Siwalik, Kasauli and Dagshai formations contain potential sandstone reservoirs. The Eocene Subathu Formation is a key exploration target in the NW Himalaya with both potential hydrocarbon source and reservoir rocks sealed by a thick clay sequence. The coeval shales within the Patala and Nammal formations are considered to be the main source rocks in the Potwar Basin, whereas, the fractured carbonates of Palaeocene and Early Eocene age are the main reservoirs. The Miocene Murree Formation is the youngest oil-producing horizon in the Potwar Basin. Palaeocene Hangu Sandstone and Lockhart Limestone are the main reservoirs in the Kohat Basin. The stratigraphy of Kohat-Potwar Basin extends into Margalla, Kalachitta and Samana Ranges. In these ranges the Jurassic-Eocene strata is exposed, so sub-thrust sheets could have hydrocarbon potential. In the NW Himalaya, the surface gas seeps are characterised by a high nitrogen content, and are either thermogenic or biogenic in origin, while the gases encountered in the wells are typically methane rich (dry) with low nitrogen concentrations, indicating thermogenic origin. There appears to be a strong linear correlation between the relative concentration of methane and nitrogen in the Himalayan fore-deep gas shows. There are numerous references to biogenic gas seeps in the Plio-Pleistocene sediments and lignite fields in the Kashmir Valley, and also in the shallow Plio-Pleistocene sediments in the Peshawar Basin. The evolution and establishment of the key petroleum system elements, the generation, expulsion, migration and accumulation (entrapment) of hydrocarbons at multiple stratigraphic levels in NW Himalaya has been controlled by the regional tectonic events. These events are associated with the source rock burial and maturation history, coupled with hydrocarbon generation, ‘peak oil’ and subsequent migration occurring concomitantly with the peak activity along the major regional thrusts. The complex and variable structural geometries have allowed a variety of traps beneath sections where source rocks have adequate burial depth, and where traps have not been breached. In NW Himalaya, the key to understand the direct relationship between tectonics and the evolution of petroleum systems are the accurate estimates for the timing of the related tectonics and that of the hydrocarbon generation, accumulation and critical moment. Here, the exploration has been hampered by the structural complexity, difficult terrain, drilling complications and poor seismic data quality. Timing of the trap formation vs. hydrocarbon charge, trap integrity, seal presence and capacity, and reservoir quality are the key geological risks that have to be addressed.

中文翻译：

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印度和巴基斯坦西北喜马拉雅的石油系统和碳氢化合物潜力

摘要 喜马拉雅造山运动塑造了该地区的沉积盆地，在从前寒武纪到新近纪的多个地层水平上，连续变形形成了“常规”和“非常规”石油系统。由于喜马拉雅山适宜的构造沉积环境、油气显示以及在东部和西部地区大致相似的构造环境中发现商业油气发现，因此人们认为喜马拉雅有油气勘探前景。尽管详细的地表地质测绘、地质数据的获取和井的钻探极大地提高了对喜马拉雅西北部的地质和构造环境以及油气潜力的了解，但商业发现在很大程度上仍然难以实现。在喜马拉雅西北部，主要感兴趣的前寒武纪-寒武纪层序包括盐岭组（Potwar 盆地），以及小喜马拉雅和亚喜马拉雅的一些层序，例如元古界 Sirban 石灰岩组；在克什米尔和 Bhadarwah-Chamba 盆地更远的东北部，以及 Garhwal 群和东南部的 Krol 带。小喜马拉雅和特提斯喜马拉雅（以克什米尔、Zanskar-Spiti、Kinnaur-Uttarakhand 和 Kumaon 盆地为代表）内出露的古生代沉积岩经历了低品位变质作用，目前没有显着的生烃潜力。Cambrian Khewra 和 Permian Tobra 地层在东 Potwar 形成含油气储层。印度北部赞斯卡特提斯喜马拉雅山的古生代地层与巴基斯坦白沙瓦盆地的地层相似。厚泥质层序是古生界内最好的潜在烃源岩层位。特提斯喜马拉雅的中生代和早始新世系列沉积在特提斯洋的浅南缘。在喜马拉雅西部，特提斯喜马拉雅系列在克什米尔、赞斯卡尔、昌巴和斯皮蒂盆地出露。中生代系列包括富含有机物质的泥质沉积物的厚层序。三叠系和侏罗系地层在Potwar 盆地东部普遍不发育或不存在，而在Potwar 盆地西部和Kohat 盆地西部增厚。侏罗纪砂岩是探明储层，并且存在潜在的烃源岩。克什米尔盆地的中生代序列以三叠纪地层为代表。一些页岩含有有机质（OM），可以代表有活力的烃源岩，而一些灰岩、白云岩和砂岩具有足够的储层特征。Zanskar-Spiti盆地（拉达克喜马拉雅）中生代-第三系泥质沉积物的OM含量适合生烃。喜马拉雅造山带新生代前陆盆地受晚中新世-第四纪南移逆冲系统变形。次喜马拉雅带包含一系列新生代沉积岩，分为 Subathu 和 Dharamsala (= Murree) 地层以及 Siwalik 组。烃源岩存在于 Subathu 和 Dharamsala 地层中；而Lower Siwalik、Kasauli 和Dagshai 地层包含潜在的砂岩储层。始新世 Subathu 组是喜马拉雅西北部的一个重要勘探目标，其潜在的烃源和储集层均被厚粘土层序封闭。Patala 和 Nammal 组内的同期页岩被认为是 Potwar 盆地的主要烃源岩，而古新世和早始新世的裂缝性碳酸盐岩是主要的储集层。中新世 Murree 组是 Potwar 盆地最年轻的产油层。古新世汉古砂岩和洛克哈特石灰岩是科哈特盆地的主要储层。Kohat-Potwar盆地的地层延伸到Margalla、Kalachitta和Samana Ranges。在这些范围内，侏罗纪-始新世地层出露，因此次冲断层可能具有油气潜力。在喜马拉雅西北部，地表气体渗漏的特点是氮含量高，并且是热成因或生物成因，而井中遇到的气体通常富含甲烷（干燥），氮浓度低，表明热成因。喜马拉雅前深部天然气显示中甲烷和氮的相对浓度之间似乎存在很强的线性相关性。在克什米尔山谷的上新-更新世沉积物和褐煤田以及白沙瓦盆地的上新-更新世浅层沉积物中，有许多关于生物气渗漏的参考资料。油气系统关键要素的演化与建立、生成、排挤、喜马拉雅西北部多个地层水平的油气运移和聚集（截留）受到区域构造事件的控制。这些事件与烃源岩的埋藏和成熟历史以及油气生成、“石油峰值”和随后的运移有关，这些迁移与沿主要区域逆冲断层的峰值活动同时发生。复杂多变的构​​造几何形状允许在烃源岩具有足够埋藏深度且未突破圈闭的部分下方存在各种圈闭。在喜马拉雅西北部，理解构造与油气系统演化直接关系的关键是准确估计相关构造的时间和油气生成、聚集和关键时刻的时间。这里，由于结构复杂、地形复杂、钻井复杂和地震数据质量差，勘探工作受到阻碍。圈闭形成时间与碳氢化合物充注、圈闭完整性、密封存在和容量以及储层质量是必须解决的关键地质风险。