Here’s a summary of the key points:

Abstract

• Exploration: Pertamina has conducted extensive surveys since 1989, covering geological, geophysical, and geochemical aspects.
• Findings: The area spans over 50 km², with indications of a liquid-dominated reservoir overlain by a steam zone. Temperatures in slim holes reached 210°C.
• Current Status: Development halted due to economic and political crises, with plans to recommence within five years.

Introduction

• Location: Ulubelu is in Lampung Province, 80 km west of Tanjungkarang.
• Features: The area includes hot springs, fumaroles, and hydrothermally altered rocks, indicating geothermal activity.
• Exploration History: Surveys began in 1989, with detailed geophysical surveys and drilling conducted in the early 1990s.

Geological Setting

• Geology: The area lies in a volcano-tectonic depression, with a history of volcanic activity since the Lower Miocene. Drilling revealed andesite, dacite, claystone, and sandstone.
• Alterations: Hydrothermal alterations have been ongoing for thousands of years, suggesting a significant heat source.

Geophysics

• DC-Resistivity and MT Surveys: Identified structural trends and conductive areas, suggesting hydrothermal alteration zones.
• Gravity and Magnetic Surveys: Revealed anomalies related to topography and potential intrusive rocks.

Drilling Results

• UBL-1: Encountered temperatures up to 210°C, indicating both conductive and convective heat transfer.
• UBL-2 and UBL-3: Encountered similar temperatures but varying permeability.

Geochemistry and Geothermometry

• Reservoir Characteristics: Indications of a liquid-dominated reservoir with temperatures potentially reaching 250-260°C at greater depths.
• Recent Cooling: Evidence suggests recent cooling in the shallow part of the system.

Geothermal Reservoir Model

• Structure: A primary liquid reservoir lies below 1500m, with a steam zone above. Heat sources may include intrusions beneath local mountains.

Business Aspects and Future Developments

• Partnerships: Various attempts to form partnerships for development, but progress stalled due to economic crises.
• Future Prospects: Development is expected to resume once the economic and political situation stabilizes.

Conclusions

1. The Ulubelu prospect covers over 50 km², with distinct northern and southern areas.
2. The geothermal system is liquid-dominated with a steam cap, potentially heated by intrusions.
3. Standard exploration methods and shallow drilling have provided a preliminary model, but further exploration is needed.
4. Development may take five or more years due to current economic conditions.

Acknowledgements

• Appreciation to Pertamina’s management and Dick Benoit for reviewing the manuscript.

This summary provides a comprehensive understanding of the document’s contents regarding the Ulubelu geothermal area. If you need more detailed information from specific sections, please let me know!