A 3D model of the Chachimbiro geothermal system in Ecuador using Petrel

Abstract

The Chachimbiro Geothermal System is the most important geothermal prospect in Ecuador. Various geothermal models have been presented based on geological, geochemical and geophysical data collected at different epochs. Currently the Chachimbiro prospect is ready to enter the exploration drilling phase. This is why it is important to identify the best drilling targets. The Petrel software allows the combination of all surface exploration data in order to identify different geothermal anomalies and create a 3D model to visualize all features of the system. This model uses lineaments as boundaries of the system based on structural mapping and locations of earthquake epicentres. The heat source is related to magma chambers that feed the main volcanic vent but is also controlled by faults, which influence possible up-flow. This up-flow is located beneath a cap rock (0-10 Ωm) and is related to a high resistivity core, which shows a concave shape (30-70 Ωm). The Na/K geothermometers show temperatures of around 240°C, however, the water in Chachimbiro has poor equilibrium with the rock. Resistivity analysis shows possible temperatures from 200 to 250°C, but this range of temperature does not represent the current temperature of the system. The origin of the fluids in Chachimbiro is meteoric based upon isotopic analysis.

The interaction between this fluid, with the up-flow into the sub-surface, forms a possible reservoir. Hot springs and gas manifestations (CO2-H2S) are out-flows of the system, which also indicate volcanic activity in the system and are expressions of the reservoir at the surface. The intersection between Chachimbiro and Azufral faults and the Chachimbiro Fault have been identified as drilling targets in the system, which could be reached by directional drilling from three different locations. These location have been chosen by combining the structural features, the resistivity anomalies, possible out-flow and up-flow zones, the hydrothermal areas and temperature anomalies which were modelled and analysed in Petrel.