Presentation Information
[2K0101-11-07]Rock porosity and permeability characterization by integrating petrophysical, hydrochemical, and microtextural analyses for geothermal resource exploration in the Rungwe and Songwe prospects, Tanzania
○Nyora Donald Kobare1[Student presentation: Doctoral course], Koki Kashiwaya1, Taiki Kubo1, Jacek Scibek2, Katsuaki Koike1 (1. Kyoto University, 2. TetraTech Inc., Vancouver)
Chairperson: 桑谷 立（JAMSTEC）
Keywords:
Portable permeameter,Hydrothermal alteration,SEM-EDS microtextures,Travertine facies,East African Rift
Understanding permeability structures in faulted rifting volcanic terrains is essential for assessing geothermal resources. For this, we integrate petrographic and microstructural investigations of drill-core and outcrop rocks from the Rungwe Volcanic Province and Songwe Rift in southwest Tanzania. In total, 28 samples from basalts, pyroclastics, meta-pegmatites, and travertines are analyzed for dry bulk density, connected porosity, and permeability using a portable pressure‑decay gas probe permeameter. Complementary thin-section petrography and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) characterize pore morphologies and alteration minerals. The measurement results are density values from 1.26 to 3.09 g/cm³, connected porosities between 0.3 and 75.5 %, and permeabilities spanning five orders of magnitude (10⁻19–10⁻14 m2). The highest permeabilities are observed in brecciated pyroclastic tuffs and banded travertines, while basalts and meta-pegmatites are nearly impermeable. SEM-EDS characterizes secondary calcite and clay infilling, micro-fractures, and vesicular networks controlling permeability. Moreover, integration of petrophysical and textural data reveals that alteration and microfractures, rather than lithology alone, dominate fluid pathways. These parameters, together with structural mapping and 35 hydrochemical indicator samples including Na/K and Cl/(HCO3+CO3) ratios, are used to define a fault-controlled permeable zone in the geothermal system, where travertine mounds act as discharge points for HCO3‑rich waters flowing through conduits above a fractured-basement reservoir. Our results provide the essential conceptualization of the permeability structure and resource distribution in the rift systems.