松辽盆地肇州区块沙河子组层序格架特征及其对沉积和烃源岩的控制作用

以Vail经典层序地层学理论为指导,综合利用钻井岩心、地震、测井及地化分析测试等资料,通过地震反射特征分析、小波变换法、声波时差曲线和电阻率曲线交汇图法多种方法,将松辽盆地肇州地区下白垩统沙河子组整体划分为1个二级层序和由下至上的SQ1SQ4 4个三级层序。其中:这4个三级层序均具有二分结构,发育湖侵和湖退两个体系域;顶部的SQ4遭受严重剥蚀,在盆缘地带仅残留湖侵域。在层序地层单元划分和对比的基础上,结合研究区构造活动背景、物源供给情况等因素,认为研究区沙河子组主要发育西部扇三角洲、东部辫状河三角洲和湖泊相3种沉积相类型,而沉积体系演化主要受控于层序格架发育情况,表现为"格架控砂、继承演化、分源沉积、连片发育"的特征。在底部SQ1和顶部SQ4发育时期,盆小而水浅,西部扇三角洲和东部辫状河三角洲展布范围较小,扇体多呈朵叶体状分布,此时,泥岩含量低且有机质丰度差,优质烃源岩基本不发育;在SQ2和SQ3发育时期,湖盆持续水进造成盆阔而水深的沉积背景,加之物源供应充足,形成了扇体连片发育的特征,其中,水下分流河道作为前缘亚相中的主力砂体存在,而湖相暗色泥岩厚度大、品质好且有机质丰度高,在SQ2和SQ3最大湖泛面附近发育两套最优质的烃源岩。

Sequence Stratigraphy Characteristics and Its Control Action on Sedimentary and Source Rock in Shahezi Formation of Zhaozhou Area in Songliao Basin

Based on Vail's sequence stratigraphy theory,the sequence stratigraphy framework of Early Cretaceous Shahezi Formation in Zhaozhou area in Songliao basin is established through the study of cores,seismic data,logging data, and other materials. Shahezi Formation is one second grade sequence, and it includes four third grade sequences from the bottom to the top,SQ1-SQ4. Each third grade sequence develops dichotomy structure,transgressive system tract, and regressive system tract. Among them,Top SQ4 suffered serious erosion, its transgressive system tract exists only in the basin margin. Based on the contrast of the sequence stratigraphic division,combined with the background of the tectonic activity,source supply, and the other conditions in the study area,three types of sedimentary facies were developed in Shahezi Formation:fan delta in the west, braided river delta in the east, and lake facies. The sedimentary evolution was mainly controlled by the development of the sequence stratigraphy as described:"stratigraphic control sand body,sedimentary facies development inheritance,sedimentary deposits from different provenance and development regionally". In the development of SQ1 and SQ4,the basin was small and water was shallow. The lobate fan delta and the braided river delta distribute in a small range,the content of shale is low and the abundance of organic matter is poor; while in the stages of SQ2 and SQ3,both water and other source supply entered adequately into the lake basin, this resulted in the contiguous development of the fan-shaped body (lake facies?), in which the dark mudstone is large and thick with abundant organic matter. In addition, the underwater distributary exists as the main sand body in the leading edge subfacies. In such a sedimentary environment, two sets of optimal hydrocarbon source rocks were developed during the largest lake flooding period in SQ2 and SQ3.