MSc defence by Vincent Koech

Vincent Koech, M.Sc. Fellow in Mechanical Engineering at the University of Iceland will give a lecture on his MSc project on Tuesday 23 September, 2014 at 15:30 in the Main Building, room 220.

The title of the project is:

Numerical Geothermal Reservoir Modelling and Infield Reinjection Design, Constrained by Tracer Test Data: Case Study for the Olkaria power plant

Vincent's supervisors are: 

Andri Arnaldsson, Geothermal Reservoir Specialist at Vatnaskil Consulting Engineers, Guðni Axelsson, Director Geothermal Training at ISOR and Halldór Pálsson, Senior Lecturer at the Faculty of Industrial Engineering, Mechanical Engineering and Computer Science at the University of Iceland. 

External examiner will be Lárus Þorvaldsson, Specialist in Geothermal System at Vatnaskil Consulting Engineers. 

Everyone's welcome to attend.

Abstract

Numerical simulation of geothermal reservoirs is a very useful instrument for developing strategies of field exploitation, production well location and reinjection scheme design. Reinjection of spent geothermal fluids serves to maintain reservoir pressure and enhance energy extraction efficiency over the life of the resource. Tracer testing is used as tool for tracing flow within a geothermal system for the purpose of characterizing the system and to gain good understanding on inherent heterogeneity. Tracer transport is orders of magnitude faster than cold-front advancement around reinjection boreholes and can be used as a cooling predicting tool. This study involved interpretation of tracer test data collected during cold injection into well OW-12 in the Olkaria geothermal field in Kenya. A single fracture model showed well OW-15 to be the most affected by the cold reinjection and OW-19 to be the least affected. A pessimistic version of the model predicts well OW-15 to cool by more than 20°C and wells OW-18 and OW-19 to cool by about 6°C for a forecast period of 15 years. An optimistic model version predicts well OW-15 to cool by 13°C, OW-18 to cool by 1°C and OW-19 to cool by 2°C for the same period. A numerical reservoir model was developed for the Olkaria East and Southeast fields, covering an area of 27 km2. The natural state model matched well available temperatures and pressure data as well as being validated by production history data. Thermal front propagation was captured by the numerical reservoir model and thermal front breakthrough for well OW-15, which is the most affected well, takes about 4 years at an injection rate of 30 kg/s according to the model. This compares well with the pessimistic single fracture model prediction. Well OW-12 in Olkaria can be used as a cold reinjection well, but it has to be used intermittently according to the results of the study, injection for one year followed by a period of recovery. The current injection depth in well OW-12 is shallow, but model calculations show that if reinjection depth is considerably deeper (-2600 m a.s.l.), longer injection periods are possible without collapse of the steam cap involved.