莺歌海盆地泥岩稳定压实带成因及石油地质意义

莺歌海盆地为快速沉积、沉降的伸展-转换盆地,泥岩压实为常见的指数压实模式,同时,泥岩压实曲线具有典型的稳定压实带:即明显偏离正常压实趋势线,其声波时差值基本保持在约300μs/m,厚度一般为700~1000m,岩性主要以莺-黄组深海—半深海相泥岩为主,为孔隙度基本稳定段,但其测试地层压力却为正常静水压力.分析了泥岩声波稳定压实带的层位、岩性组合、热演化剖面、气测烃及与黏土矿物转化带的关系,认为其形成并非只与黏土矿物转化有关,中央凹陷带底辟区的泥岩稳定压实带是黏土矿物转化和流体排放共同作用形成的,非底辟区则是局部流体排放造成的结果.稳定压实带普遍位于超压带顶面上部,反映出稳定压实带实际上为超压系统的封闭层,强烈底辟区稳定压实带的消失则可能表明深部超压流体向浅部的排放,油气则可能主要集中在浅部层位.因此,正确识别稳定压实带对于准确预测欠压实引起的偏离正常压实趋势线的超压及油气聚集分布具有重要的理论和实践意义.

Genesis and petroleum geology significance of the stable compaction belts of mud layer in Yinggehai Basin

Yinggehai Basin is a youthful Genozoic sedimentary basin with extend and transformation.The compaction curves of the mud layer are of exponential model,and they are of the characters of the compaction curves of typical stable compaction belts:they obviously deviate from the trend of normal compaction curves,their acoustic travel time is about 300 μs/m,the depth of them generally is 700～1 000 m,their lithology is mainly the mud rock of abysmal-bathyal facies,the porosity of them is stable,but their measured formation pressure is normal hydrostatic pressure.Through the analyses of the horizon,lithology combination,geothermal evolution profile,gas logging and epigenesis of clay minerals on the layer,it is held that the formation of the stable compaction belt is not only related to the transform of the clay minerals,and the formation of the stable compaction belt of the mud rock in the diapir area of the central sag belt is the result of the combined action of clay mineral transformation with fluid drainage,the formation of the stable compaction belt of the mud rock in the non-diapir area of the central sag belt is the result of local liquid drainage.The stable compaction belts generally locate in the upper part of the top surface of super pressure belts,which shows that the stable compaction belts are actually the sealing layers of the super pressure systems.The disappearance of the stable compaction belts in intense diapir areas may indicate the drainage of the super-pressure fluid from deep zone to shallow zone,and hydrocarbon may accumulate in shallow layers.Then,the correct recognition of the stable compaction belts is of important significance to the accurate prediction of the super pressure deviated from normal compaction trend curves caused by uncompaction and hydrocarbon accumulation distribution.