Sediments Evolution of Napo Formation in the Slope Belt of Oriente Basin—A Case Study of Block T

The Napo Formation of the Oriente Basin plays an important role in the hydrocarbon exploration and production of the Ecuador. This study is based on the data of T block which is located in the eastern part of Ecuador. Evolution sequence is divided through seismic and logging data; facies is determined by core description for each sequence; and finally, the sediment evolution of the Napo Formation can be delineated clearly. The Napo Formation is a transgressive system, where five sequences were formed with the changing sea level. Superimposed retrogradational facies is typical in these sequences. Facies analysis indicates that “T,” “U,” and “M1” units are tide-dominated estuarine deposits involving tidal channel, tidal bar, sand flat, and marsh. In addition, residual delta sandstones were found in the lower part of the “M1” unit, but which is distributed in restricted zones and is hard to identify. Those delta sandstones may indicate that there is a delta before the tide-dominated estuarine deposits. Sedimentary facies changed to shallow-marine shelf in the upper parts of the sequences due to the rising sea level, and marlstone deposited. Based on the facies and sequence study, the sedimentary system and sediments evolution can be known in the Napo Formation. This is helpful to understand the sedimentary conditions of the Napo Formation in the slope belt of the Oriente Basin.