塔里木盆地下寒武统肖尔布拉克组丘滩体系类型及其勘探意义

Types of mound-shoal complex of the Lower Cambrian Xiaoerbulake Formation in Tarim Basin,northwest China,and its implications for exploration

基于钻井岩心、薄片以及露头的详细研究,根据地貌背景、沉积物类型和沉积特征差异,将塔里木盆地肖尔布拉克组缓坡丘滩体划分为4种类型:颗粒滩型、丘滩型、滩坪型和台坪型。颗粒滩型主要发育于塔中-巴东地区的"平台"地貌背景下,以鲕粒和砂屑等高能沉积片状发育为特征;丘滩型发育于柯坪-巴楚地区的匀斜缓坡背景,以微生物丘和藻砂屑滩发育为主,呈"小丘大滩";滩坪型发育于阿克苏地区,微生物丘不发育,颗粒滩和潮坪相大面积发育;台坪型发育于轮南-牙哈区,具类似"孤立台地"特征,东侧边缘陡,发育高能丘滩沉积,西侧较缓,以低能微生物丘/席为主。不同类型丘滩体系的储层差异明显,颗粒滩型和滩坪型以Ⅱ类储层为主,分布稳定,有利于储层规模发育;丘滩型和台坪型可发育Ⅰ类储层,储层呈块状分布,具规模优质储层发育潜力。提出塔中-巴东地区应以寻找岩性圈闭为目标,柯坪地区应寻找构造相对稳定、保存条件较好的目标,轮南-牙哈区高能丘滩带值得探索。

Based on the observation of cores and thin sections,as well as the detailed survey of outcrops,the ramp mound-shoal complexes of the Lower Cambrian Xiaoerbulake Formation of Tarim Basin can be divided into four types:grain beach,mound shoal,shoal flat,and platform inner flat,in accordance with their differences in geomorphology,sediment category,and sedimentary features.The grain-beach type complex,occurring in relatively flat platform settings in the Tazhong-Badong area,is characteristic of high-energy oolites and intraclastic grainstones growth in slices.The mound-shoal type complex,occurring in ramp settings in the Keping-Bachu area,is characterized by the prosperity of microbial mounds and algae-intraclastic grainstone shoals,displaying a feature of large shoals interspersed by small mounds.The shoal-flat type complex usually occurs in Aksu area with absence of microbial mounds and widespread grain beaches and tidal flats.The platform-inner-flat type complex is developed in the Lunnan-Yaha area,characterized by “isolated platform” with a steep eastern slope (filled with high-energy mound shoal deposits) and a relatively gentle western slope (dominated by low-energy microbial mounds or mats).Reservoirs in different mound-shoal complexes developed distinctive features. The grain-beach and shoal-flat types usually develop Type Ⅱ reservoirs with consistent distribution over large areas;while the mound-shoal and platform-inner-flat types tend to develop Type Ⅰ reservoirs,which are blocky and high-quality reservoirs,and may distribute in a large scale.In conclusion,lithologic traps should be a focus of exploration in the Tazhong-Badong area.While much attention should be paid to those tectonically stable traps with good preservation conditions in the Keping area,the high-energy mound-shoal complexes should be the exploration target in the Lunnan-Yaha area.