Exploring Paka Geothermal Reservoir through 3D Visualisation and Gravity Data Inversion Modelling in Northern Kenya Rift
Abstract
The Paka geothermal field, located in the Northern Kenya Rift segment, is influenced by tectonic extension and magmatic activity that drives crustal uplift and hydrothermal circulation. While most previous gravity studies in this region targeted depths beyond 6 km, shallow intrusive structures crucial for geothermal resources remain poorly resolved. This study applied regional Bouguer anomaly mapping and 3D gravity inversion to characterise density variations, intrusive heat sources, and favourable structural settings for resource development. Gravity data were processed with a Bouguer density of 2.0417 g/cm3, anomaly separation through upward continuation, and 3D VOXI inversion in Geosoft Oasis. Results reveal a broad negative Bouguer anomaly (–126 to –103 mGal) about 20 km wide, with superimposed narrower anomalies (~5 km wide) in the northern caldera. These align with NW–SE, NE–SW, and N–S fault trends, consistent with regional tectonic structures. Near-surface pyroclastic sediments (0–250 m, 2.1–2.3 g/cm3) overlie a denser caprock (250–700 m, 2.25–2.45 g/cm3) interpreted as hydrothermally altered tuffs. At ~2.5 km depth, low-density zones (1.75–1.8 g/cm3) suggest water reservoirs or altered tuffs. A high-density mafic intrusion, likely of trachytic to basaltic magma origin, was identified between 2.0 and 3.1 km depth (volume ~475 ±10 % km3; 2.50–2.90 g/cm3), serving as the primary heat source. The associated reservoir beneath the summit lies at ~2.2 km depth with an estimated volume of 120 ±10 % km3. Structural continuity links Paka to Silale and Korosi volcanoes along the rift axis. The findings of this study highlight the summit region as the most promising drilling target for sustainable geothermal development.
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