台湾西南海域深水地区探勘愿景

Prospect in Deepwater Exploration in Offshore Southwestern Taiwan

盆地深水区的石油探勘一直是世界油公司扩展油气藏的重要目标之一，90年代由於层序地层学的发展导致了深水探勘的革命，西非地区掀起了一股深水探勘的热浪和耀眼的成绩。随着海上油气探勘技术的进步已征服了具有挑战性的环境，可以预期的是每年都会有重大的油气发现。台潮石油合约区东南测勘区是由中央隆起带划分南北兩个凹陷带，形成二凹一隆的基本构造形式。北部凹陷条件比较好，因为它具有一定的封闭性。预估油气生成量经模拟结果发现，东南测勘区汕头凹陷文昌组生油源岩的排油量为9.85亿吨，约相当72.2亿桶的原油。文昌组生油源岩油气资源量为1.97亿吨，约相当14.4亿桶的原油。东南测勘区内主要发现有九个主要的构造目标，其中以汕头A构造成为本研究区最主要的目标构造，具有构造与低位扇的双重目标组合。台南盆地南缘深水区、台潮石油合约区东南测勘区及珠江口盆地白云凹陷展现同样的构造形式；位於珠江口盆地中央隆起区之神狐隆起区－番禺低隆起－东沙隆起区－澎湖－北港高区等600公里长的构造坝（名词引自孟昭彝等（1976））南缘半地堑之裂谷盆地，该盆地经歷了裂谷盆地之构造演化与後期的岩浆活动，酸性火成岩组成的古潜山形成一障蔽岛（Barrier Island），其间的距離发育了约50～60公里的断陷带（Rift-subsidence Basins Zone），这些断陷带岩层的沉积体系都具有23.8～18.5百万年前之间低位扇（Lowstand Fan）的沉积体系域的共同性。珠江口盆地的白云凹陷已在这个沉积体系域发现巨量的油气，而同位在断陷带的台潮石油合约区东南测勘区与台南盆地南缘深水区有着同样的沉积体系，断陷盆地的潜力是无穷的。然而，唯一需要注意的是不同的断陷盆地（Rift-subsidence Basin）需要良好的砂岩做为储集岩，这些储集岩需要分布范围广、储集层的厚度厚的低位扇，才能提供封储油气所需的储集层。而裂谷盆地面积的大小及盆底的深浅，系提供成熟的油气源的基本要素。这兩点是未來研判各盆地是否进行探勘、开发的主要依据。因此，未來台潮合约区东南测勘区之探勘可考虑在汕头A构造区先进行三维震测，以确保构造的准确性与油气的资源量的估算，做为未來钻探与开发的依据。

Petroleum exploration in deepwater basin is one of the primary targets to expand the oilgas reserves for global oil industries. The development of stratigraphy sequence in 1990s resulted in the revolution in deepwater exploration. Since then, deepwater exploration spreaded into the offshore West Africa, which resulted in the growth of oil and gas findings. The advanced techniques subsequently developed for the offshore oil and gas exploration have overcome the severe environmental challenges. It could be predictable that, the main oil and gas findings will be reported in the following each years.Architecture of explored area, southeastern Taichao Petroleum Contracted and Region, is composed of two depressions and one raise. The two depressions are aligned in the south and north and are separated by the central raise. The evaluated petroleum system in the northern depression is better than the southern one, due to the discrepancy closure conditions of the two depressions. The estimated generation for oil and gas in place, simulated from the source rock, Wenchang Formation, in the Shantou Depression of the explored region, is ca. 9.85 billion metric tones which equals approximately 72.2 billion barrels of crude oil. The resource estimated for the source rock, Wenchang Formation, is ca. 1.97 billion metric tonnes, which equals approximately 14.4 billion barrels of crude oil. Nine leads are recognized in the southeastern explored region. The lead Shantou A is the main prospect, characterized by the structure and the lowstand fan.An identical structural architecture is displayed in the deepwater region of the Tainan Basin, the explored region of the southeastern Taichao Petroleum Contracted Region and the Baiyun Depression of the Pearl River Mouth Basin. A rift basin with half-graben morphology developed in the southern slope of the structural dam (refer to Meng et al. (1976)) that is with 600 km in length extending from the Shenhu uplift in the Pearl River Mouth Basin, through the Panyu Low uplift and the Dongsha raise, to the Penghu-Pekeng rising area. The basin experienced the rift basin structural evolution and the magma activity in later stage. A buried hill composed of acidic igneous rocks acted as a barrier island. A rift-subsidence basins zone was developed in the interval between the southern slope of structural dam and the buried hill. An identical depositional system tract recognized in the strata of the riftsubsidence basins zone is the lowstand fans built up in the age between 23.8 Ma and 18.5 Ma. The exploration of the lowstand fans in the Baiyun Depression of the Pearl River Mouth Basin experienced the findings with large amount of oil and gas. This identical depositional system tract is also recognized in the explored area of southeastern Taichao Petroleum Contracted Region and the deepwater region of southern slope of the Tainan Basin. It can be drawn that, the petroleum potential in the rift-subsidence basins is behind imagine. Nevertheless, one thing that needs to be noticed is, high quality sandstone is an essential to be the reservoir in the rift-subsidence basins. The essentials of reservoir characterization for oil and gas trapping and accumulation are the lowstand fans with the characteristics of widespread in lateral and thick thickness in vertical. Besides, the area and depth of the rift basin are essentials for the generation of matured oil and gas. The two issues are the crucial basis for further determining whether the exploration and development will be continued or not. For raising the assurances of the structural resolution and the resource estimation, the 3D seismic data will be the basis for the future well design and development. Therefore, acquiring the 3D seismic survey in the lead Shantou A might be one of the considerations for next steps to explore the southeastern Taichao contracted and explored region.