琼东南盆地中中新统古沟谷和坡折带特征及油气勘探意义

摘要

Through comprehensive study on the seismic data,well logging data,sedimentary facies,paleogeomorphology analysis,the paleo ravine and slope-break zones of the mid-Miocene in Qiongdongnan basin were identified,and the developmental feature,distribution rule and control over sedimentary of the paleo ravine-slope break zones were emphatically analyzed.The hydrocarbon reservoir forming conditions and distribution regularity of the lithologic reservoirs developed under the environments were discussed.The results show that there are three types of paleo ravine,including "V"shape,"U" shape and dish-like shape,and "V"or "U"ravine generally developed in Ledong sag and Lingshui sag,while the dish-like ravine developed in Baodao sag.Three types of slope-break zones developed,such as depositional slope-break zone,fault slope-break zone and flexure slope-break zone with certain distribution regularity.The depositional slopebreak zone mainly developed in Ledong sag and Lingshui sag;the fault slope-break zone developed in Lingshui sag and Songnan sag;and the flexure slope-break zone developed in Baodao sag.Different slope-break zone has different influence on sedimentary.Submarine fans with rich sand developed in Ledong sag and Lingshui sag and are the main reservoir in the study area,which were controlled by depositional slope-break zone with strong hydrodynamic environment.They developed widely with characteristics of coarse grain and good physical property.Submarine fans in Lingshui sag were controlled by fault slope-break zone to some extent,which developed at the downthrown of fault named lobate complex fanbodies.Submarine fans in Baodao sag with bad physical property were controlled by flexure slope-break zone where the hydrodynamic power was weak,and thus have fine grains.Comprehensive analysis shows that some zones in Ledong sag and Lingshui sag near the slope-break zones are favorable to form lithologic reservoirs,and should be the future exploration targets in deep water area.%根据地震、录井和测井等资料,利用沉积相识别、古地貌恢复等方法,分析琼东南盆地中中新统古沟谷和坡折带的发育特征、分布规律及其对沉积的控制作用,探讨在其背景上发育的岩性油气藏的成藏条件和分布规律.研究结果表明:研究区发育“V”型、“U”型及宽缓碟型3类古沟谷,乐东凹陷和陵水凹陷北坡易形成“V”型或“U”型古沟谷,宝岛凹陷北坡发育宽缓碟型古沟谷;坡折带可分为沉积坡折带、断裂坡折带和挠曲坡折带3种类型,乐东凹陷和陵水凹陷北坡发育沉积坡折带,陵水凹陷和松南凹陷北坡发育断裂坡折带,宝岛凹陷北坡发育挠曲坡折带.不同类型坡折带对沉积具有差异性控制作用,表现为乐东凹陷和陵水凹陷北坡发育受沉积坡折带控制的大型富砂海底扇,是研究区主要的储层,该沉积时期水动力强、发育规模大、粒度粗、物性较好;断裂坡折带对陵水海底扇沉积的控制作用表现在断层下降盘发育朵叶复合体等有利沉积微相;挠曲坡折带控制宝岛凹陷发育的海底扇沉积,该沉积时期水动力较弱、粒度细、物性较差.综合分析认为,乐东凹陷和陵水凹陷北坡坡折带是岩性油气藏发育的有利区带,是下一步深水勘探的重要区域.