Infield re-injection straegies in Olkaria, Kenya : based on tracer studies and numerical modelling

Abstract

In two-phase geothermal reservoirs, efficient heat mining process can be achieved by injecting deep into the liquid zone at an optimum rate that will maintain the boiling level at the same depth while producing from a shallower level. Optimum resource utilization in Olkaria East production field requires intermittent infield re-injection around the central part of the field followed by a temperature recovery period. Numerical methods can be used to model fluid flowpaths in fractured two-phase reservoirs. Tracer tests can be used to calibrate such models. Reservoir cooling under varied injection scenarios can then be predicted. In this report, a two-dimensional fracture model analysis, resulting from tracer and injection tests conducted in well OW-12, is presented. Wells OW-12 and OW-19 are connected at depth by an 800 m deep by 400 m wide and 1 m thick fracture. Cold and hot re-injection into well OW-12 at 8 kg/s will cool the formation by 55°C and 25°C, respectively, in twenty years. Cold injection can be done for 11/2 years followed by a similar recovery period.