| Abstract |
The single porosity numerical reservoir model of the San Jacinto geothermal system, Nicaragua has been created and developed over the past 3-4 years. Recent reservoir tracer studies have shown a connection between an injection well and the main production area. In order to assess the significance of this link in terms of reservoir management, a quick and effective numerical model update was required. When considering the impact of injection returns in a reservoir, the associated thermal impact of injection returns is of critical importance. The matching of temperature declines by injection returns in a single porosity reservoir can be limited due to the relatively large volumes of the model blocks and heat diffusion from reservoir block surfaces. Travel times and return volumes are often very difficult to match. Dual porosity modelling introduces the ability to model fracture flows, and as such provides a mechanism to achieve closer matching of injection returns. It is widely accepted that the conversion of single porosity numerical models to dual porosity models is a difficult and highly time consuming process due to the increased computational requirements, the introduction of additional matching parameters such as fracture volume, porosity, permeability and spacing, and the inherent difficulty in acquiring field measurements for these parameters. Discrete fracture network (DFN) models can be implemented as an alternative approach; however these also require significant re-gridding and calibration if applied to existing models. In order to achieve the desired level of calibration in an appropriate timeframe, we considered an alternative approach to matching the reservoir tracer injection returns while still using the single porosity model. Given that the connection between the injection well and production area had been interpreted to be structural with linked feed zones, a distinct fractured zone or channel between the injection well and production area was selected to represent the fault structure. Within this fault structure, the volume of each block was reduced and assigned a high porosity. Anisotropic permeability calibration was also performed to attain a good match to injection returns. This approach has been termed |