Advanced Reservoir Characterization in a Low Resistivity Gas Play Offshore Ecuador

Abstract

The Amistad field in the Guayaquil Gulf in Ecuador, located at the east of the Nazca subduction zone with the South America plate, and at the west of the Andes Mountains, is in a zone suffering from an intense tectonic activity. It is divided into various structural block very heterogeneous in term of hydrocarbon content. Since the beginning of the development of this gas field in the shallow water of the Gulf of Guayaquil, various challenges has been encountered. Certain drilled wells gave unsatisfactory production test and the project economics has been questioned, meanwhile the Ecuadorian industry gas demand is increasing. Today it becomes critical to reach the production objectives. An unclear identification of the sand bodies due to a poor log signature, a difficult estimation of the water saturation and a challenging quantification of the irreducible and clay bound water volumes with conventional logs lead in some cases to water production. A tailor-made workflow focusing on resolving these challenges has been built. The use of spectroscopy measurements, when available, permits to identify masked sand bodies. Its integration with triaxial resistivity tools permits to identify gas-bearing low resistivity zones and estimate the water saturation, while the nuclear magnetic resonance permits to quantify the amount of non-movable water. This new methodology shows a significant improvement of the understanding of the reservoir in the new drilled wells, but how to populate this information acquired with modern technology to the old wells? A method using the nuclear magnetic resonance information from the new wells in combination with the effective porosity per electro-facies permitted to populate a model through the whole field. It permits to solve for the irreducible water saturation, one of the most critical information in this field. The production results on the last three wells where this methodology has been applied are a clear indicator of the success of this workflow leading to production well test a lot above the expected one, meanwhile the production behavior of the older wells is now well understood.