琼东南盆地梅山组浊积扇分类及其勘探意义

Classification of turbidite fans of Meishan Formation in Qiongdongnan Basin and their exploration significance

琼东南盆地中新统梅山组浊积扇是南海北部天然气勘探的重要目标,浊积扇类型与储层发育程度密切相关。根据海平面变化、海底地形地貌、同生断裂组合等因素,将琼东南盆地梅山组浊积扇分为陆棚扇、斜坡扇和盆底扇三大类。高位域主要在陆棚或陆棚边缘沉积陆棚扇,低位域晚期主要在陆坡区沉积斜坡扇,盆底扇发育于低位域早期,可进一步划分为断阶盆底扇、断控缓坡末阶盆底扇、断控陡坡根部盆底扇、朵状盆底扇、峡谷切割盆底扇、局限盆底扇。浊积扇类型和物源体系是影响储层物性的重要控制因素。断阶盆底扇、峡谷切割盆底扇和朵状盆底扇储层发育,是重要勘探目标。断控陡坡根部盆底扇、陆棚扇、斜坡扇沉积分异较差,泥质含量高,勘探风险相对较大。断控缓坡末阶盆底扇和局限盆底扇颗粒细、泥质含量高,是勘探需要规避的类型。琼东南盆地西段乐东-陵水区物源供应充足,各类扇体储层发育,而中段宝岛区及长昌区距物源区较远且供应不足,碎屑颗粒细、泥质含量高,好一优质储层欠发育。

The turbidite fans of Miocene Meishan Formation in Qiongdongnan Basin are important targets for natural gas exploration in the northern South China Sea,and the types of turbidite fan is closely related to reservoir development.The turbidite fans of Meishan Formation in Qiongdongnan Basin can be divided into shelf fans,slope fans,and basin floor fans according to the factors of sea level change,submarine topography,and syndepositional faults.The shelf fans at the shelf or shelf edge and the slope fans at the slope zone are mainly deposited in the highstand system and the late lowstand system respectively.The basin floor fans deposited in the early lowstand system can be further divided into six types:fault-terrace basin floor fan,final-terrace basin floor fan of faultcontrolled gentle slopes,basin floor fan of fault-controlled steep slope roots,lobate basin floor fan,basin floor fan cut by canyons,and confined basin floor fan.The turbidite fan type and provenance system are important controlling factors affecting reservoirs'physical properties.The reservoirs of fault-terrace basin floor fans,basin floor fans cut by canyon,and lobate basin floor fans are developed and are important exploration targets.Due to poor sedimentary differentiation and high mud content,the exploration risks are relatively large in the basin floor fans of fault-controlled steep slope roots,shelf fans,and slope fans.Final-terrace basin floor fans of fault-controlled gentle slopes and confined basin floor fans have fine grain and high mud content,which should be avoided in exploration.The various fan reservoirs are developed due to the sufficient provenance supply of Ledong-Lingshui area in the western part of Qiongdongnan Basin;however the excellent and high-quality reservoirs are underdeveloped due to the fine detrital particles and high mud content,and the lack provenance supply of Baodao area and Changchang area in the middle part of Qiongdongnan Basin,which are far away from the provenance area.