Application of Pulsed Neutron Elemental Spectroscopy Logging to Source Rock Evaluation-A Case Study in a Limestone of Napo Formation in Oriente Basin

The Oriente Basin have large oil resources. The main production zone is the clastic rock reservoir of the Napo Formation in Cretaceous and the main source rocks is black shale and argillaceous carbonate rock of the Napo Formation. Previous studies have suggested that crude oil in the Oriente Basin mainly comes from shale, and there has been little research on carbonate rocks as source rocks. During the exploration and development process of the Oriente Basin, carbonate rock production layers in several oil fields were discovered. During recent exploration in the northern Oriente Basin, it was discovered that there are several A limestone abnormally thickened zones. The seismic amplitude was significantly enhanced and the formation pressure increased abnormally. Industrial oil flow was obtained in the A limestone formation for the first time after actual drilling. An advanced cased hole Multifuncition Spectroscopy tool was used to obtain formation elements and derive mineral composition, TOC, movable fluid saturation and matrix parameters. The result shows that the mineral composition of the A limestone formation is mainly calcium carbonate, containing illite, potassium feldspar and pyrite indicate that its deposition in the relatively deep -water environment; it is a high-quality source rock with high TOC content. It shows the good exploration and evaluation prospects in the A limestone in northern of Oriente Basin.