南海北部陆缘白云深水区油气地质特征与勘探方向

Petroleum geology characteristics and exploration direction in Baiyun deep water area,northern continental margin of the South China Sea

烃源岩分布特征不明、大型构造圈闭缺乏、成藏层系单一和储层条件复杂是南海北部陆缘珠江口盆地白云深水区(包括白云凹陷和荔湾凹陷)油气勘探面临的关键问题。从构造、沉积到成藏的综合性研究表明,陆缘岩石圈强烈薄化背景下的伸展拆离作用控制了陆缘深水区盆地的形成与演化,陆缘岩石圈强烈伸展的结构特征控制了裂陷期规模烃源岩的分布,陆缘地壳强烈薄化带控制了拗陷期陆架坡折带和深水储层的发育与分布,从而导致白云深水区的深部结构、沉积充填及油气成藏等具有特殊性,与典型陆相断陷及国外深水地质差别明显。在此基础上,建立了白云深水区大型陆架边缘三角洲-深水重力流体系油气成藏模式,认识到生烃过程中形成超压、晚期断裂活动和底辟带泄压是有利的成藏动力过程,继承性古鼻状隆起带和断裂-构造脊复合输导体系控制了油气富集成藏,从而导致白云深水区呈现油气兼生、内气外油的特征,形成了白云东洼油气区、白云西洼油气区、白云北坡气区和白云东油气区等四大油气优势聚集带,同时还发育了白云西南断阶带、白云南洼、荔湾凹陷及南部超深水勘探潜力区。

The unknown distribution patterns of source rocks, lack of large structural traps, singular accu- mulation layer and complex reservoirs are the challenges for petroleum exploration in Baiyun deep water ar- ea（including Baiyun sag and Liwan sag）of Pearl River Mouth basin on the continental margin of northern South China Sea. The comprehensive research of tectonics, sedimentary and hydrocarbon accumulation shows that the formation and evolution of continental marginal basin is controlled hy the extension and de- tachment in an intensive lithosphere thinning setting. This extension also controls the source rock distribu- tion during rifting period. Crustal thinning controls the development and distribution of shelf breaks and deep water reservoirs during depression period. It results in the distinctiveness of deep structures, deposi- tion and hydrocarbon accumulation, which are very different from typical non-marine rifting basins and oversea deep water areas. The petroleum accumulation pattern in a shelf edge delta-deep water gravity flowsystem of Laiyun deep water area is further established based on understanding the basic geology in the ar ca. The overpressure during hydrocarbon generation, late faulting activity and pressure release of diapirs are the favorable accumulation dynamic processes. Successive uplifting and complex migration system of fCmhs-ridges control the hydrocarbon accumulation, resulting in the simultaneous generation of oil and gas, inner gas and outer oil accumulation pattern. Four major hydrocarbon accumulation zones including Baiyun east sag zone. Baiyun west sag zone, Baiyun northern slope zone and Baiyun east zone develop in the area. Moreover. potential zones such as southwest step-fault zone, t3aiyun south sag. I.iwan sag. and southern uhra-deep water area also develop in this area.