Evaluation on Productivity Index Distribution on Wayang Windu Geothermal Field to Identify Potential Production from Deep Brine Reservoir Section

Abstract

As part of reservoir management, performance of production wells in Wayang Windu field is evaluated using wellbore hydraulic models that have been calibrated to match the production history of each well with WELLHIST application. The calibrated models should accurately represent well geometry, the location and productivity index (PI) of each permeable zone, and the historical evolution of pressure and enthalpy at each zone. The established wellbore models are typically used to forecast the deliverability of individual wells as reservoir conditions continue to evolve. In addition, PI profile that represents the distribution of fracture permeability can also be analyzed on vertical resolution with the goal of defining potential production from deep brine reservoir. An empirical correlation between permeability as a function of depth for Wayang Windu reservoir is resulted from this study. Despite having 20 years of production history, fracture permeability in deep liquid reservoir remains as key uncertainty for future reservoir performance due to low number of wells that have been drilled to this part of reservoir. Currently, more than 90% of steam production is delivered from the shallow steam cap reservoir. The study suggests that the potential steam production gain from the well drilled to liquid reservoir section (200 m BSL elevation) is 16 kg/s with potential upside of 28 kg/s and chance of regret of 10%. Result from this study has also been used as reference to determine minimum depth of well that drilled in 2019 drilling program to delineate vertical extension of fracture permeability.