准噶尔盆地腹部超压层分布与油气成藏

Distribution of overpressure stratum and its relationship with hydrocarbon accumulation in the central part of Junggar Basin

准噶尔盆地腹部普遍发育深层超压系统,超压段具有高声波时差、低电阻率以及低地震速度的响应特征。盆地腹部不同地区超压层分布的深度范围不同,其中盆1井西凹陷为4000～7000 m,东道海子北凹陷和昌吉凹陷东部为5000～9000 m,昌吉凹陷中部和西部为6000～10000 m。超压大多顺层分布,只是在各凹陷边缘以及凹陷内部的局部地区有穿层上拱现象。超压顶面分布的层位由北向南、从东到西逐渐变浅,即从三叠系顶部过渡到白垩系底部。准噶尔盆地腹部的超压为成岩压实后由晚期生气作用和封闭层围限共同作用形成的,油气主要分布在超压顶面附近。深层超压是油气运移的驱动力,超压层分布与深部次生孔隙发育带的形成密切相关,与超压配置的输导体系和储集空间对油气成藏有着重要的控制作用。

The deep zone overpressure system is commonly developed in the central part of Junggar Basin （deeper than 4000 meters）. The analyses of drilling, geology, logging and seismic data of the overpressure section show that the overpressure zone is characterized by the overpressure response of high acoustic travel time, low resistivity and low seismic velocity. The depth of overpressure strata in the central part of Junggar Basin differs in different sags. The western sag of Pen 1 Well has the depth from 4 kilometers to 7 kilometers, and the northern sag of Dongdaohaizi area and the east part of Changji Sag have the depth from 5 kilometers to 9 kilometers, and the center and west parts of Changji Sag have the depth from 6 kilometers to 10 kilometers. Most of the overpressure system were distributed along bed, and layer penetration could be found in the margin area and some local areas of the sag. The top of overpressure strata distribution are getting shallow from north to south and from east to west. Those strata transferred from the top of the Triassic to the bottom of the Cretaceous. As probably hydrocarbon-originated and post-diagenesis-stage overpressure in the central part of Junggar Basin, oil and gas were mainly accumulated around the top of overpressure strata. The deep overpressure was the driving force of hydrocarbon migration. The distribution of overpressure strata controlled the formation of secondary porosity zone and accumulation of hydrocarbon.