塔里木盆地塔河地区中下奥陶统沉积特征及其演化模式

Sedimentary Characteristics and Evolution Model of Middle and Lower Ordovician in Tahe Area,Tarim Basin

沉积环境对岩溶型储层的发育起着基础性作用,影响着岩溶体的规模和强度,加强沉积环境研究有助于优质岩溶储层的勘探与预测。为深入认识塔河地区中下奥陶统沉积特征,在野外调查基础上,结合岩石颜色、类型、组合、结构、构造、古生物、地球化学特征等岩石学和岩相学标志,利用岩心、测录井、地震和区域宏观沉积资料,对中下奥陶统沉积环境进行了精细识别和划分。结果显示,研究区岩石类型主要为颗粒灰岩、泥晶灰岩、生物灰岩和过渡岩类;共发育5种沉积环境,蓬莱坝组以局限—半局限台地为主,鹰山组以半局限台地、开阔台地为主,一间房组以开阔台地、台地边缘、淹没台地为主;共发育11种地震相,与各类沉积相带具有较明显的对应关系。总的来说,研究区以台地相为主,时空演化差异明显。纵向上,自蓬莱坝组至一间房组沉积水体逐渐加深,沉积环境由局限逐渐变为开阔;横向上,研究区主体以开阔台地、台地边缘为主,向东、向南至研究区外部逐渐过渡为斜坡、盆地相。综合前人资料,建立了研究区自下奥陶统蓬莱坝组局限台地→半局限台地→中下奥陶统鹰山组开阔台地→中奥陶统一间房组台地边缘→一间房组晚期、吐木休克组淹没台地的演化模式。

The environment plays a fundamental role in the development of karst reservoirs and affects the scale and strength of karst bodies.Strengthening the study of sedimentary environments can be beneficial to the exploration and prediction of high-quality karst reservoirs.In order to deeply understand the sedimentary characteristics of the Middle and Lower Ordovician in Tahe area,the sedimentary environment is finely identified and divided by using core,logging,seismic and regional macro-sedimentary data on the basis of field survey.At the same time,the petrological and petrographic indicators,such as rock color,type and combination,structure,paleontology,geochemical characteristics,and so on,are also used to identify sedimentary environments.The results show that the rock types in the study area are mainly granular limestone,micritic limestone,biological limestone and transitional rocks.There are five types of sedimentary environments developed in total.The Penglaiba Formation is dominated by restricted and semi-restricted platform,and the Yingshan Formation is dominated by semi-restricted platform and open platform,while the Yijianfang Formation is dominated by open platform,platform margin and submerged platform.A total of 11 seismic facies are developed,which have an obvious corresponding relationship with various sedimentary facies.In general,the study area is dominated by platform facies,with obvious differences in space-time evolution.Vertically,the sea waterbody gradually deepens from the Penglaiba Formation to the Yijianfang Formation,and the sedimentary environment gradually changes from restricted to open platform.Laterally,the main body of the study area is dominated by open platform and platform margin,and gradually transits to slope and basin facies from east and south to the outside of the study area.Based on previous data,the evolution model of the study area is established.This model shows that the sedimentary environment has evolved gradually from restricted platform of the Lower Ordovician Penglaiba Formation→semi-restricted platform→open platform of the Middle and Lower Ordovician Yingshan Formation→platform margin of the Middle Ordovician Yijianfang Formation→submerged platform of the late Yijianfang Formation and the Tumuxiuke Formation.