彰武盆地九佛堂组—沙海组沉积充填特征及盆地演化

Sedimentary filling characteristics of Jiufotang Formation-Shahai Formation and evolution in Zhangwu Basin

通过ZW3井和ZW10井沉积层序对比和I1地震剖面的平衡地质剖面分析,对彰武盆地沉积充填特征和盆地演化进行综合研究。九佛堂组与沙海组在地层叠置关系上存在3种不同叠置样式:萎缩式、一致式和超越式,是由盆地发育过程中右旋扭动造成的。九佛堂下段为盆地伸展拉张背景下的充填,发育大段泥岩和油页岩,反映可容纳空间增大和沉积物供给不足;该段具有较好生油气能力。九佛堂组上段为转换伸展背景下的充填,ZW10井代表的东部区发育大套泥岩,而ZW3井代表的西部区发育一套粗碎屑沉积,反映盆地走滑或者扭动作用的发生;走滑扭动断裂作用使得断陷中形成凸起,分隔了生烃凹陷,而且开始形成下部成藏组合。九佛堂组末期为盆地构造反转期,发生了较大规模构造反转,致使盆地东部边缘区域的九佛堂组上段遭受严重剥蚀。沙海组下段为断陷由伸展到构造扭动背景下的充填,其下部暗色泥岩发育,具有较好生油气能力;上部ZW3井和ZW10井砂岩含量明显增加,反映伴随着沉积物的足量供给与快速进积;构造扭动使盆内凸起再次发育,形成了上部成藏组合。沙海组上段为盆地萎缩背景下的充填,砂体强烈进积,盆地萎缩。沙海组末期盆地再次发生大规模构造反转,沙海组上段地层遭受强烈剥蚀。

A comprehensive study of sedimentary filling characteristics and basin evolution in Zhangwu Basin is presented in this paper by comparing the sedimentary sequences of Well ZW3 and Well ZW10 analyzing and a balanced geological section of I1 seismic profile. There are three varied superimposed stratal relationship styles between Jiufotang Formation and Shahai Formation,including back-stepping（ fading）,still-standing and over-stepping styles,which are caused by the right lateral wrench during the basin development. A large amount of mud and oil shale developed in the lower member of the Jiufutang Formation during the stage of extension,reflecting the increased accommodation space and the shortage of sediment supply. The potential capacity of oil and gas is good in this member. The filling of the upper member of Jiufotang Formation had formed during the stage of transtension.Well ZW10,representing the filling of the eastern region of the basin,is a set of mudstones and Well ZW3,representing the western region,is a set of coarse clastic deposits,reflecting the occurrence of slip-wrench of this basin.The uplift in the fault depression resulted from slipping and wrenching of the faults,had separated the hydrocarbongenerative depressions and the lower reservoir system started to develop. The large-scale of tectonic inversion occurred at the ending of Jiufotang Formation and a serious erosion on the eastern edge of the basin made the upper member of the Jiufotang Formation partly lost. The filling of the lower member of the Shahai Formation developed during the stage of extension-transtension. The dark shale with good potential capacity of oil and gas developed in the lower part and the content of sandstones in both Well ZW3,and Well ZW10 had an obvious increase in the upper part,reflecting adequate supply and rapid progradation of sediments. The slipping and wrenching had made the uplift develop again and form the upper reservoir system. The filling of the upper member of Shahai Formation occurred during the stage of basin fade with a strong sand progradation. A big scale of tectonic inversion occurred again at the ending of the Shahai Formation and the upper member of the Shahai Formation was largely lost.