沾化凹陷渤南洼陷古近系压力特征及成因机制

Pressure characteristics and formation mechanisms of Paleogene in Bonan sag,Zhanhua depression

根据实测压力、泥岩声波时差等资料,对沾化凹陷渤南洼陷地层压力的分布特征、演化规律及其超压形成机制进行分析。结果表明:渤南洼陷实测地层压力随深度的变化呈现明显的'二台阶'式,第一台阶对应着2.35 km,该台阶之上表现为常压,之下开始出现低幅度超压;第二台阶对应地层埋深为3.0 km,该台阶之下超压明显,压力系数可达1.8,其中沙三中下、沙四上亚段是异常高压发育的主要层系;欠压实和生烃作用是渤南洼陷异常压力形成的主要原因,且超压机制存在区域差异,中部断阶带和南部缓坡带表现出明显的欠压实现象,其深度范围与超压的第一台阶相对应;深洼带超压泥岩的密度则随埋深的增加而增大,与成熟生烃范围匹配较好,生烃作用是该区的主要增压因素,且深度与第二台阶相对应;研究区欠压实与生烃导致沙三段压力的增加幅度不同,两因素具有各自的增压量化模型,导致地层压力出现了'二台阶'的特征。

By utilizing measured pressure and mudstone sonic log interval, the distribution characteristics and evolution of the pressure of Bonan sag in Zhanhua depression were analyzed, and the overpressure mechanisms were studied. The results show that variation of measured fluid pressure with depth exhibits ＂two steps＂： When buried depth is lower than 2.35 kilometers, the formation pressure is basically shown as normal pressure; Low amplitude overpressure starts to appear between the depth of 2.5 kilometers and 3.0 kilometers ; The highest pressure coefficient can be as large as 1.8 between the depth of 3.0 kilometers and 4.0 kilometers, the Es3^z, Es3^ x and Es4s are the main formations where overpressure developed. The unbalance compaction and hydrocarbon generation are the main mechanisms of overpressure, and the regional difference exists. With the increase of depth in the middle step-fault zone and southern slop, the unbalance compaction phenomenon appears obviously and the range is corresponding to the first step; In deep sub-sag belt, over-pressured mudstone＇s density increases with the increase of the depth, but matches well with the range of the hydrocarbon generation. Hydrocarbon generation is the main pressuring mecha-nism in this zone and the depth range is corresponding to the second step. The amplitude of overpressure caused by unbalance compaction and hydrocarbon generation differs from each other, they both have their own pressure increasing quantified model which leads （o the appearance of the ＂two steps＂ characteristics of the formation pressure.