Geology of the Campanian M1 sandstone oil reservoir of eastern Ecuador: A delta system sourced from the Amazon Craton
Abstract The Campanian M1 sandstone Member of the Napo Formation is one of the main reservoirs of the Capiron-Tiputini oil play system of the eastern part of the Oriente Basin of Ecuador. This study presents a geological model for this reservoir at the Apaika and Nenke oil fields included within the Block 31, and the Eden Yuturi oil field, operated by PETROAMAZONAS EP. The geological characterization of the M1 sandstone is based on an integrated study, which includes core description, electric log analyses and seismic data interpretation. The sedimentological descriptions from available cored sections show that M1 sandstone records a variety of fluvial to shallow marine processes, including mass flow and delta-front turbidity currents not previously documented. The stratal stacking pattern interpreted from electric logs indicates that the succession reflects deltaic progradation rather than the backstepping pattern typically displayed by the underlying Albian to Santonian sediments of the Napo Formation. Seismic RMS amplitude defines clinoform geometries with sigmoidal sand body architecture prograding from east to west. Correlation with neighboring regions in Colombia suggest that the M1 sandstone was probably part of a large river-dominated delta system sourced from the east during major Campanian progradation. The location of the source area of sediment was determined using U-Pb detrital zircon dating. Provenance ages are uniform within the M1 Sandstone cluster in a population that ranges from 1.4 to 1.6 billion years. These ages indicate that sands were derived mostly from erosion of the lithotectonic Rio Negro-Jurena province, located to the northeast of the studied area. Detrital ages from the overlying Maastrichtian Tena Formation include ages between 80 and 200 Ma pointing to an important change in the source areas, located in the Eastern Cordillera of Ecuador. The change in sediment supply from east to west recorded in the Tena Formation coincide with the initial episodes of the Andean orogeny, and may be driven by the collision of fragments of the Caribbean large igneous province (CLIP) against the continental margin of northwestern South America.