南美奥连特盆地坎潘阶碳酸盐岩建隆的识别及科迪勒拉运动早期抬升对Main-M1储集层沉积的控制作用OACSTPCD

The Main-M1 sandstone is becoming an important exploration target for structural-litholo-gical 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 deve-loped,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 10m.As the uplift and carbonate build-up were developed prior to the deposition of the Main-M1 sand reservoir,the palaeomorphology may thus in-fluence 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 palaeo-morphology reconstruction in the fore-deep of the Oriente Basin.