基于岩心沉积构造、古生物及其组合,结合测井相、地震相分析,对巴西桑托斯盆地M油田下白垩统的沉积环境与沉积相进行了深入研究,提出一种新的沉积微相分类方案.研究表明:研究区下白垩统I组主体为淡水开阔湖泊滨浅湖沉积,发育介壳滩、颗粒滩、滩间洼地、浅湖灰泥、滩缘、滑塌扇等沉积微相,局部为咸水丘滩型等湖泊滨浅湖沉积,B组为咸水丘滩型滨浅湖沉积,发育藻丘、颗粒滩、丘缘、滩缘、丘间洼地、藻灰坪等沉积微相.自下而上,湖盆水体逐渐变浅,呈现从I组以介壳滩-颗粒滩为主转变为B组以藻丘-颗粒滩为主的沉积格局.研究区湖相碳酸盐岩形成主要受控于古地貌、湖平面变化及水体介质的变化.构造沉降和湖平面变化控制可容空间,水体介质的变化控制生物类型,进而控制沉积微相类型,为沉积主要控制因素.藻丘及介壳滩等高能相带主要发育于古隆起部位,沉积厚度大,分布范围广,呈近南北向和北东—南西向展布,研究区东部迎风一侧发育颗粒滩,规模相对较小,丘间、滩间、浅湖灰泥等低能相带则主要发育于低洼部位.

Based on the sedimentary structure, paleontology and lithology combinations of cores, combined with the analysis of logging facies and seismic facies, the sedimentary environment and facies of Lower Cretaceous in M Oilfield of Santos Basin were studied, and a new sedimentary facies classification scheme was proposed. The research shows that: it is an open littoral-shallow lake sedimentary environment with freshwater of Formation I in the study area, which includes microfacies of coquina shoal, granular shoal, inter-shoals, shallow lake marl, shoal margin, and slump fan, it is mound-shoal type littoral-shallow lake sedimentary environment with salt water sediments of Formation B, which includes algal mound, granular shoal, mound margin, shoal margin, inter-mounds, and algal marl flat. From the bottom to the top, the water body gradually become shallow, showing a sedimentary pattern that changes from the coquina shoal granular shoal dominated in Formation I to algal mound-granular shoal dominated in Formation B. The stratigraphy of lacustrine carbonate rocks in the study area is mainly controlled by paleogeomorphology, lake level and water medium. Structural subsidence and lake level control the accommodating space, and water media controls the types of organisms, which in turn controls the types of sedimentary facies. These are the main controlling factors for sedimentary. The high-energy facies such as algal mound and coquina shoal are mainly developed in the paleo-uplifts, with large thickness and wide distribution, and they are distributed in a near north-south and northeast-southwest direction. Low-energy facies such as inter-mounds, inter-shoals, and shallow lake marl are mainly developed in lower parts of paleogeomorphology.