Abstract
The Upper T Sandstone of the Tarapoa Block in the Oriente Basin of Ecuador demonstrates low resistivity despite often containing light gravity oil, the presence of which has been confirmed through tests and production. This situation merits an in-depth analysis to better understand the reasons for, and the impact of, the low resistivity as a key factor in conventional petrophysical analysis; and in so doing, improve the precision of determining the hydrocarbon content and productive potential of the Upper T reservoir in the Tarapoa area.
At first, it was considered that the principle cause of the low resistivity effect in the Upper T interval was the presence of glauconite which is deposited in a shallow marine environment, however, upon more thorough investigation, it was determined that, despite the real impact of glauconite, there are a number of other variables which contribute to this anomaly, such as thin bed sand/shale alternations, grain size variation in the sandstones, and the vertical resolution of the conventional wireline tools typically used.
A thorough analysis and understanding of the Upper T reservoir rock is justified in order to determine its real hydrocarbon potential, and to help in the calibration of the reservoir potential when proposing well locations. In addition, a better understanding of the variables impacting the reservoir quality and flow characteristics is of great importance when proposing test intervals and in the design of testing and production parameters.
