渤海湾盆地济阳坳陷古近系异常高压成因及其与陆相页岩油富集的关系

Abnormal pressure genesis and its relationship with continental shale oil accumulation in Paleogene, Jiyang Depression, Bohai Bay Basin

为了探索渤海湾盆地济阳坳陷地层异常压力对页岩油富集的影响,运用全岩X-衍射分析、常规热解生烃潜力分析和有机地球化学系统分析等方法,研究了4口页岩油专探井古近系的单井地层压力结构、泥页岩岩相、有机质成烃演化、黏土矿物转化、烃类滞留—次生孔隙和微裂缝分布的关系。研究区靠近洼陷中部的古近系沙河街组沙三中、下亚段和沙四上亚段岩相组合以碳酸盐岩为主,而靠近凹陷边缘以碎屑岩/化学岩混合沉积组合为主。利用声波测井、密度测井和钻录井资料,可有效识别单井压力结构和异常高压特征,并揭示生烃洼陷区以碳酸盐—黏土矿物组合为主的富有机质页岩中地层孔隙压力的影响因素。综合应用地球化学证据证实,济阳坳陷古近系地层超压主要来源于成熟泥页岩的生烃增压,泥页岩自源超压段与滞留烃高峰段及次生孔隙发育带相对应。

In order to explore the effect of abnormal pressure on shale oil accumulation in the Jiyang Depression,Bohai Bay Basin,the formation pressure distribution,muddy shale lithofacies,hydrocarbon generation evolution of organic matters,clay mineral conversion,hydrocarbon retention,and the distribution of secondary pores and microfractures in each of four exploration wells specially for Paleogene shale oil were studied by total rock X-ray diffraction analysis,conventional pyrolysis analysis on hydrocarbon generation potential,systematic analysis on organic geochemistry,and other methods.In the study area,the lithofacies association in middle and lower submembers of the third member (Es3middleand Eslower)3,and upper submember of the fourth member (Es4upper) of Paleogene Shahejie Formation adjacent to subsag center is mainly carbonate rocks,while near sag margin,there are primarily mixed sediments of clastic rocks/chemical rocks.Based on the data from sonic,density and drilling loggings,pressure distribution and abnormal pressure characteristics in single well could be identified effectively;in addition,the factors that affect formation pore pressure in organic shale containing major association of carbonate and clay minerals could be uncovered.Comprehensive application of geochemical evidences confirmed that Paleogene overpressure in the Jiyang Depression was mainly originated from hydrocarbon generation pressurization in mature muddy shale.Self-source overpressure intervals in muddy shale are in correspondence with the zones of secondary pore development and peak hydrocarbon retention.