基于物理模拟实验的天然气幕式动态成藏模式——以琼东南盆地宝岛凹陷北部断阶带为例

Natural gas episodic accumulation mode based on the physical simulation experiments:A case study of the northern step-fault zone of the Baodao Sag in the Qiongdongnan Basin,South China Sea

南海北部琼东南盆地深水区宝岛凹陷北部断阶带资源潜力巨大,然而深水深层天然气输导体系不清、运聚过程不明,制约了该地区乃至南海北部的油气勘探进展。因此,基于琼东南盆地深水区宝岛凹陷北部断阶带构造沉积与储层特征,建立地质模型,并设计3种模拟宝岛凹陷北部断阶带天然气运聚的物理模型,据此开展油气成藏物理模拟实验,深入分析研究区主要通源断层在不同启闭条件下对天然气成藏的影响。结果表明:①断层封闭性和储层相带、物性是控制天然气运聚的重要因素,而由于超压驱动作用,断层封闭性具有相对性:断层在封闭状态下,对天然气运移起到遮挡作用,但随充注压力的增加具备幕式开启的可能,且断层在开启状态下对天然气运移无遮挡作用;②在陵水组三段与三亚组二段砂体厚度及物性相同条件下,天然气沿开启性断层垂向运移优于侧向运移;③在陵水组三段与三亚组二段砂体厚度及物性不同条件下,半封闭性断层幕式开启导致天然气在断层两盘物性更好的陵水组三段砂体中存在幕式动态成藏过程。研究成果为宝岛凹陷北部断阶带的天然气输导体系与运聚过程研究提供理论指导,对琼东南盆地乃至南海北部深水深层油气勘探具有借鉴意义。

In the Qiongdongnan Basin of the South China Sea,the northern step-fault zone of the Baodao Sag has great resource potential,but the unclear deep-water and deep-layer natural gas migration and accumulation process restricts the progress of oil and gas exploration in this region and even in the northern part of the South China Sea.Therefore,based on the sedimentary structure and reservoir characteristics of the northern step-fault zone of the Baodao Sag in the deep-water area of the Qiongdongnan Basin,a geological model is established and three models of physical simulation experiments are designed to simulate the migration and accumulation pro⁃cesses of natural gas in the northern step-fault zone of the Baodao Sag,focusing on the influence of the main faults on natural gas accumulation under different opening and closing conditions.The results show that:(1)Fault sealing property,reservoir facies zone and physical properties are important factors to control the natural gas migration and accumulation,while fault sealing property is relative due to over pressure driving effect:the fault plays a blocking role in the natural gas transport in the closed state,but with the increase of the filling pres⁃sure,it has the possibility of episodic opening,while the fault has no blocking effect on natural gas transport in the open state.(2)Under the same conditions of sand thickness and physical properties of the third member of the Lingshui Formation and the second member of the Sanya Formation,the vertical migration of natural gas along the fault is better than that of the lateral migration.(3)Under the conditions of different thickness and physical properties of the sand bodies of the third member of the Lingshui Formation and the second member of the Sanya Formation,the episodic opening of the semi-closed fault leads to the episodic and dynamic accumula⁃tion process of natural gas of the third member of the Lingshui Formation with better physical properties.The re⁃search results provide theoretical guidance for clarifying the process of natural gas migration and accumulation in the northern step-fault zone of the Baodao sag,which has important enlightenment for deep-water and deep-lay⁃er oil and gas exploration in the Qiongdongnan Basin and even in the northern part of the South China Sea.