Perpustakaan Digital ITB

In Indonesia, geothermal production process is generally estimated into 30 years of production time to generate electricity. By the time of production activity, geothermal reservoir condition may encounter a naturally production decline. Naturally production decline is a decline rate excluding production decline due to wellbore flow assurance issue such as scaling. There is an urge to maintain the production for achieving its target for the rest of production time with effects of pressure depletion by developing production decline model to predict future production performance. Production decline analysis is an adapted method from petroleum industry to visualize the decline trend of steam production rate against the time. This study aims to develop a production decline method using exponential decline model into a vapor dominated reservoir at Patuha Geothermal Field which has been operated for 8 years and could generate 60 MW of electricity and to find the most suitable value of field decline rate which represents the whole reservoir. This model is an underestimation of the reserves that could be generated. Before we could calculate the production decline rate, we have to derive the data normalization. It starts with generate the deliverability test which adapted from standard gas deliverability equation. It shows that the decline rate in the productivity of a steam well (normalized for a standard flowing wellhead pressure) and the decline rate in static wellhead pressure are corresponded. From the generated model, we also need to validate the decline rate results with the deliverability curve model for each feed zone per year. And it resulted a variance of decline rate for individual wells. For the field decline rate, by analyzing 8 out of 10 existing production wells, it resulted 2.7% per year.