Discovery of Mesozoic strata in the eastern region of offshore Pakistan and its oil and gas significance
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摘要:
巴基斯坦海域历经60余年油气勘探，长期以新生界为主要目标，对中生代地层展布、构造演化特征等认识不清。巴基斯坦东部海域中—新生代时期经历了复杂的构造—沉积演化过程，新生代受喜马拉雅隆升影响而沉积了巨量陆缘碎屑物质，因此是研究诸多重大基础科学问题的极佳场所。受白垩纪晚期区域火成岩影响，对该区中生代地层是否存在、如何展布等问题一直存在较大争议，这极大限制了区域油气勘探活动的开展。本研究基于新采集的高品质二维地震剖面，突破了火成岩层的屏蔽作用，通过地震反射界面刻画、地震波组特征分析和层速度分析等手段，揭示了中生代地层在巴基斯坦东部海域广泛分布，中生代地层受控于同期活动的强烈伸展断陷作用，被隆坳相间的构造古地理格局分割在多个规模不等的次级凹陷内部。整体厚度800～10000 m，表现为东南厚、西北薄，向北和向西超覆，最大沉积厚度位于研究区东南和西北两个区域，该套地层在陆域下印度河盆地已证实为重要烃源岩层，因此海域中生代地层的发现有效拓展了该区未来油气勘探方向和潜在价值。
Abstract:After more than 60 years of oil and gas exploration in the offshore areas of Pakistan, the primary focus has long been on the Cenozoic strata. The distribution of Mesozoic formations and the tectonic evolution remain unclear. The eastern offshore areas of Pakistan underwent a complex tectonic-sedimentary evolution during the Neogene. Influenced by the Himalayan uplift during the Neogene, a significant amount of detritus from continental margin deposited, making it an excellent location for studying numerous fundamental scientific questions. Due to the impact of regional volcanic rocks in the late Cretaceous, there has been considerable controversy regarding the existence and distribution of the Mesozoic strata in the region, significantly hindering the regional oil and gas exploration activities. Based on high-quality 2D geological profiles, overcomes the previous shielding effect of volcanic rock layers. By means of seismic reflection interface delineation, analysis of seismic wave group characteristics, and layer velocity analysis, the extensive distribution of the Mesozoic strata in the eastern offshore areas of Pakistan was clarified. The Mesozoic formations, controlled by intense extensional faulting in the same period, are segmented within multiple secondary basins of varying scales, forming a paleo-tectono-geographic pattern of alternating uplifts and depressions. The overall thickness ranges from 800 to 10000 m, thicker in the southeast and thinner in the northwest. Overlapping towards the north and west, the maximum sedimentary thickness is located in the southeast and northwest regions of the study area. The stratigraphic unit was confirmed as an important hydrocarbon source rock layer in the onshore of the lower Indus River Basin, which effectively expanded the future directions and potential value of oil and gas exploration in the offshore areas.
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