Natural state modelling of a vapor dominated system : case study Darajat, Indonesia

For a mature geothermal field like Darajat, which has been operating for nearly 30 years, re-evaluating the natural state offers an opportunity to evaluate any significant differences revealed by current interpretations from expanded data sets with those presented in the early model. This study also investigates the sensitivity to relative permeability functions for production modelling. However, these cannot be calibrated due to this study being only natural state modelling. The expanded stratigraphy and resistivity models enhance comprehension in lateral distribution of reservoir rocks and cap rock in Darajat conceptual model. Meanwhile, the most recent MEQ distribution suggests the latest delineation of Darajat base of reservoir, which improves the conceptual model’s understanding of vertical extension. The improved conceptual model serves as the main basis to develop numerical model grids and inputs before re-modelling the Darajat steady state. The updated conceptual model is discretized into numerical grids by using PyTOUGH script. The enhanced conceptual model, which contains more information than the early model in 1990, enables the development of finer numerical grids. Then, the refined stratigraphy and fault models are assigned into each rock-type domain in the numerical grids. The natural state model is simulated by using AUTOUGH2 simulator. The numerical model is calibrated to the actual data by adjusting permeability input at each rock-type domain. Natural state calibrations indicate that the temperature models are well matched to the measured temperatures at majority of the pre-production boreholes. The calibrated permeability values appear to control the way heat and mass flow in Darajat system during pre-production era. The effect of linear relative permeability function in the calibrated model shows that in a low residual liquid saturation set-up vapor tends to be more mobile than liquid in single porous medium or within the small pores of rock matrix. The calibrated model, using a low residual liquid saturation set-up of 0.3 in the linear relative permeability function, produces high vapor saturation model of 0.7. If the calibrated model used for single fed production testing in the bottom block of Well G, it provides the estimation of mass flow generated from the tested block. The sensitivity analyses using various PI indicate that higher vapor saturation model from the linear relative permeability function generates higher produced mass flow.

Author dc:creator

• Hanna Melati Tampubolon 1990-

Contributors dc:contributor

• Háskólinn í Reykjavík

• Meistaraprófsritgerðir
• Verkfræði
• Endurnýjanleg orka
• Jarðhitasvæði
• Engineering
• Sustainable energy
• Geothermal fields

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/1946/53773

OAI identifier oai:identifier

oai:skemman.is:1946/53773