高频层序格架内礁型微地貌特征及其控储机理——以塔中东部地区上奥陶统为例

The Control Mechanism of Microtopography in the High Frequency Sequence Framework to Reef-Bank Complex Reservoir:An Example from the Upper Ordovician Lianglitage Formation in Eastern Tazhong Area

塔中东部地区发育上奥陶统良里塔格组礁滩相碳酸盐岩是油气产出的主力产区。为了揭示层序地层格架特征及其内部沉积微地貌特征对礁滩体储层的控制机理,本文通过对岩石学、沉积微相、古生物、测井相研究,建立了上奥陶统良里塔格组高频层序地层格架,可划分为11个四级层序和多个五级层序。研究区良三段—良二段以高位体系域垂向持续加积作用为主,是礁(丘)、滩组合镶边沉积的主要发育期,一个四级层序内可发育一个至多个礁滩体沉积微地貌旋回,礁型微地貌发育规模及厚度受海平面升降次级旋回和构造沉降控制。通过对良三段—良二段高位体系域成岩组构和成岩环境分析,认为受同生岩溶作用所形成的大气成岩透镜体主要发育在高频层序向上变浅旋回的顶部和微地貌高处。同一层序内沉积微地貌隆起和海平面相对升降变化所控制的暴露作用,以及同生期大气淡水溶蚀、淋滤作用是控制台缘礁滩体优质储层发育以及层位性和区域差异性的关键因素。集中揭示高频层序格架内微地貌特征及其对礁滩体储层的控制机理,有效指导了塔中东部地区奥陶系礁滩型油气藏勘探开发。

The reef-bank carbonatite of Upper Ordovician Lianglitage Formation in the eastern Tazhong area is the principal zone producing oil and gas.In order to find out the features of stratigraphic framework and the control mechanism of its inner sedimentary microtopography to the reef-bank complex reservoir,we established the high frequency sequence stratum framework of Upper Ordovician Lianglitage Formation in this paper,based on the analysis of lithology,depositional microfacies,welwitschiopsida and logging curves.The framework can be divided into 11four-stage sequences and multiple five-stage sequences.The second and third passages of Lianglitage Formation mainly deposited in highstand systems tract,which is characterized by continuous vertical accretion and is the main developmental phase of reef（mound）and bank combination rimmed deposits.One or more sedimentary microtopography cycles of reef-bank complex can be developed in a four-stage sequence.The thickness and scale of reefal microtopography are controlled by secondary eustatic sea level change cycles and tectonic subsidence.According to the analysis of diagenetic fabric and diagenetic environment,we believe that the atmospheric diagenetic lens formed during syngenetic karst is mainly distributed in the top of upward shallowing cycle and highland of microtopography.Exposition controlled by reefal microtopography uplift in the same sequence and sea level change in the relative movements,with dissolution and eluviation of syngenetic atmospheric fresh water are the key factors for not only the favorable reservoir development of reef-bank complex in the platform edge,but also the difference between sequences and zones.Features of high frequency sequence framework and its control mechanism to the reef-bank complex reservoir are present in this paper,which have been used to direct the exploration and exploitation of reef reservoir of Ordovician in the eastern Taizhong area and have achieved some success.