南海北部浅水区低地温断陷成藏特征及勘探启示

摘要/Abstract

摘要： 沉积盆地的地温场影响油气成烃、成储、成藏等过程，低地温盆地成藏特征有别于热盆。综合国内沉积盆地热类型差异及低地温盆地勘探实践，以南海北部浅水区西江主洼为例，总结低地温断陷成藏特征。断陷盆地裂陷期剧烈的构造活动易于形成欠补偿湖盆，可为优质烃源岩的发育提供条件；低地温梯度延缓烃源岩热演化进程，使得低地温断陷生、排烃期相对变晚，但生油窗持续时间更长，原油充注更充分；深埋砂岩储层在低温背景下抗压溶作用增强，其物性得到有效保护；低地温断陷中温度增压作用不明显，导致成藏动力较弱，油气大多优先在近源圈闭内聚集。鉴于低地温盆地的勘探现状和成藏特点，该类型盆地的勘探应围绕富生烃洼陷，以近源深层为重点，在稳定分布的区域性泥岩盖层之下，找准优质储层发育带，精细评价大胆上钻，进而打开油气勘探大场面。

关键词: 南海北部, 西江主洼, 低地温断陷, 成藏特征

Abstract: The processes of hydrocarbon generation, preservation and accumulation are influenced by geothermal fields of the sedimentary basins, thus hydrocarbon accumulation characteristics of low geothermal basins are different from high geothermal basins. In this paper, the geothermal discrepancies of sedimentary basins and the exploration practices of low geothermal basins in China were reviewed. Taking the Xijiang sag in the shallow water area of northern South China Sea as an example, the hydrocarbon accumulation characteristics of low geothermal rifted basins were discussed. Intensive tectonic activities during the rifting stage facilitated the formation of under-compensation lake basins, providing conditions for the development of high-quality source rocks. The low geothermal gradients could delay the thermal evolution process of the source rocks, thus postponing the periods of hydrocarbon generation and expulsion while extending the duration of oil window to facilitate more charge of crude oil. The deep sandstone reservoirs were more capable of anti-pressolution in low geothermal background, effectively protecting physical properties. In low geothermal rifts, the supercharging effect was not apparently sensitive to temperatures, leading to weak dynamics for hydrocarbon accumulation, in which circumstance most of hydrocarbons preferentially accumulated in near-source traps. Considering the exploration situation and hydrocarbon accumulation features of low geothermal basins, it is suggested that the petroleum exploration in such basins should focus on the hydrocarbon-rich sags, especially deep layers near the source rocks. Furthermore, efforts should be made to ascertain high-quality reservoir belts below the stably-distributed regional mudstone cap rocks. After elaborate evaluation of prospects, wells should be accurately deployed and drilled for significant exploration achievements.

Key words: northern South China Sea, Xijiang sag, low geothermal rift, hydrocarbon accumulation features

何　敏, 雷永昌, 于水明, 陈雪芳, 魏山力, 刘　培. 南海北部浅水区低地温断陷成藏特征及勘探启示[J]. 中国石油勘探, 2016, 21(4): 75-84.

He Min, Lei Yongchang, Yu Shuiming, Chen Xuefang, Wei Shanli, Liu Pei. Hydrocarbon accumulation features and exploration inspiration of low geothermal rifted basins in shallow water area of northern South China Sea[J]. China Petroleum Exploration, 2016, 21(4): 75-84.

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