| Title | Application of Methylene Blue-dye Test and X-Ray Diffractometry to Guide Drilling Operation and Refine Subsurface Model in Hululais Geothermal System |
|---|---|
| Authors | Vivi Dewi Mardiana Nusantara, Muhammad Imam Prasetya |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | In the Hululais Geothermal System, two epidote zones are encountered before reaching the reservoir system. At the shallower depth, a relict epidote formed under low-temperature condition, while a deeper epidote layer marks the current productive reservoir. During critical casing point decision, onsite Methylene Blue-dye Test (MBT) was applied, as it resolves ambiguity in using epidote as a reservoir marker. Since MBT only measures bulk clay content, detailed X-Ray Diffractometry (XRD) analysis was performed on 320 borehole samples from nine wells, to identify specific clay minerals and build a hydrothermal alteration model. The result shows distinct MBT ranges for different clay species: smectite (12–40%), kaolinite (30–40%), chlorite (3–12%), illite (≤3%), heulandite (18–40%), and wairakite (3–6%). Notably, kaolinite pinpoints the steam-heated zones in the clay cap layer. Low MBT values (<9%) mark the active reservoir zone, characterized by illite, chlorite, and wairakite. The smectite zone in the peripheral area, which often leads to drilling hazards, is actually linked to mixed volcaniclastic deposits rather than the clay cap. The study confirms strong correlation of MBT and XRD for identifying the top of reservoir and refining the clay cap distribution depicted from MT-resistivity model. |