厄瓜多尔奥 main-M1砂岩储集层是该盆地近年来重要的构造-岩性圈闭勘探目的层系,寻找砂体和岩性 main-M1砂岩勘探的关键。该盆地为晚白垩世弧后热沉降盆地和新生代前陆盆地的叠合盆地,在构造上分为西部逆冲褶皱带、中部前渊带和东部斜坡带,在前渊带发育一系列近N-S走向长轴背斜。综合观察和分析发现,在研究区内长轴背斜上生长了1个碳酸盐岩建隆,地震上具有明显的边界反射形成丘状外观和较连续的弱振幅内部反射,测井上具有厚层、近箱型低GR响应特征。该建隆表明在其沉积的坎潘阶时期,长轴背斜已经开始抬升,将背斜顶部推升至古水面附近,形成建隆局部生长的条件。压实回剥方法恢复古地貌证实,长轴背斜在坎潘阶早期开始发育,构造抬升幅度为7~10 m。由于构造抬升和建隆 main-M1沉积前,抬升古地貌可影响砂岩沉积。根据背斜上数十 main-M1砂体厚度统计,发现背斜顶部砂岩储集层整体较发育,但古建隆顶部砂层厚度减薄或者缺失,在背斜的南部延伸段,构造顶部砂岩缺失,仅在东部侧翼富集。提出了近N-S向背斜古 main-M1砂体沉积,使砂岩于富集于构造下倾方向的控砂模式。该模式可形成上倾尖灭型构造-岩性圈闭,从而提供了通过古地貌恢复在奥连特盆地前渊带寻找新圈闭的勘探思路。

The Main-M1 sandstone is becoming an important exploration target for structural-lithological plays in the Oriente Basin of Ecuador,in which accurate prediction of sand distribution and pinch-out belt is the key to successful trap definition. Oriente Basin is a retro-arc thermally subsiding basin in the Late Cretaceous and a foreland basin in the Cenozoic. It can be divided into a fold-thrust zone in the west,a fore-deep zone in the middle,and a slope zone in the east. In the fore-deep zone,there are a series of nearly N-S oriented elongate anticlines. In the anticline of the study area,a carbonate build-up is developed,which is characterized by mounded,low-amplitude but relatively continuous seismic reflections,and thick,blocky and low-amplitude GR well log motifs. This build-up may indicate that during the time of its deposition in Campanian,the anticline had begun to uplift and push its top close to the paleo-sea level. This brought about locally favorable conditions for the development of the carbonate build-up. Palaeogeomorphic reconstruction based on the back-stripping method shows that the anticline had started to uplift in the Early Campanian,ranging in magnitude from 7 to 10 m. As the uplift and carbonate build-up were developed prior to the deposition of the Main-M1 sand reservoir,the palaeomorphology may thus influence the emplacement of Main-M1. According to the statistics of Main-M1 sand thickness in dozens of wells on the anticline,the top of the anticline is overall Main-M1 sand prone,but the sand becomes very thin or absent on top of the carbonate build-up. In the southern extension of the anticline,the Main-M1 sand is absent on the structural top but becomes thicker at the downdip to the east. It is thus proposed that anticlinal paleo-morphology could influence Main-M1 sand deposition and force it to accumulate on the structural flap. This model opens up a new way of identifying structural-lithological traps through palaeomorphology reconstruction in the fore-deep of the Oriente Basin.