冀中坳陷前第三系岩溶发育规律及其控制因素

冀中坳陷自蓟县纪杨庄运动以来经历了七次较大规模的构造运动,伴随发育有七期岩溶,但只有最晚的发生于印支—燕山运动的第Ⅶ期岩溶被较多保存下来,它可划分出三个次级岩溶期。从中元古界长城系高于庄组到下古生界奥陶系峰峰组,潜山碳酸盐岩的溶蚀作用发生在多个层位,尤其是蓟县系白云岩和奥陶系灰岩岩溶现象普遍。纵向上可统计出第Ⅶ期岩溶中的全部三期次级岩溶,岩溶层位主要为蓟县系雾迷山组、寒武系及奥陶系。钻井中泥浆漏失现象普遍,其中单井泥浆漏失量最大的层位是雾迷山组,其次是奥陶系,寒武系相对最小。冀中坳陷岩溶的总体展布特征表现为水平岩溶带距古地表的深度由凹陷向凸起变大,而水平岩溶带的厚度总体呈现由凹陷向凸起减小的趋势。构造运动、多层系碳酸盐岩的发育以及多套烃源岩的生烃演化,是影响冀中坳陷岩溶发育的三个主要控制因素。

Development Rule and Controlling Factors of Pre-Tertiary Karst in Jizhong Depression,Bohaiwan Basin

Seven large-scale tectonic movements have occurred in Jizhong Depression since Yangzhuang movement during Mesoproterozoic Jixiang period,which caused seven periods of karstification but only the final period,the Period Ⅶ of karstification,that happened in the Indosinian-Yanshan Movement was preserved well. The period Ⅶ of karstification can be divided into three sub-karstification stages. Karstification occurred in many carbonate beds of buried hills from Gaoyuzhuang Formation of Mesoproterozoic Changcheng system to Fengfeng Formation of Lower Palaeozoic Ordovician system,especially common in Mesoproterozoic Jixian dolomite and Mesozoic Ordovician limestone. There are three sub-karstification stages of the Period Ⅶ in vertical and the corresponding beds of them mainly are Jixian Wumishan Formation,Cambrian and Ordovician karsts. Karst directly results in a great amount of mud loss in drillings. The mud loss of a single layer in a single well is less than 50 m3 and the total rate of mud loss reaches to 60% in every bed. The largest amount of mud loss of a single well happened in some bed of Wumishan Formation,which was up to more than 500m3. The less amount of mud loss was in Ordovician beds and the least in Cambrian one. In generally,the karst in this depression exhibits that the depth of the horizontal karst belt to the paleosurface increases from sag to arch while oppositely the thickness of the horizontal karst belt just decreases from sag to arch. It is concluded that the main controlling factors affecting development of the karstification are tectonic movement,development of multibedded carbonate rock,and evolution of several sets of source rocks.