Conceptual Model of the Structure of the Nizhne-Koshelevsky Geothermal Steam Field (South Kamchatka)
Ivan NUZHDAEV, Sergey RYCHAGOV, Ilyas ABKADYROV, Denis DENISOV, Sergey FEOFILAKTOV
[IVS FEB RAS, Russia]
Nizhne-Koshelevsky vapour-dominated geothermal steam field is related to the complex long-lived (from early Miocene to Holocene) Koshelevsky volcanic massif, which is located in the junction zone between three Kamchatka volcanic belts where the Kamchatka and the Kurile geological structures joint to each other. This is the largest steam field of this type in the Russian Far East: inferred resources are estimated to be 210 kg/sec of dry steam, which is equal to 94 megawatts [Pisareva, 1987]; the total inferred resources were estimated to be equal to 300 megawatts [Business plan..., 2001]. Liquid production tests and drilling of prospecting boreholes allowed revealing a zone of overheated steam, which goes to a depth of more than 1.5 km. The drilling allowed penetrating to a multiple phase subvolcanic intrusion of diorites–diorite porphyries; the steaming zone is spatially located in its apical part. The Nizhne-Koshelevsky steam field is associated to the zone of a deep strike-slip fault of the east-west trending (radial to the structure of the Koshelevsky volcanic massif). Rocks in this zone are generally crevassed and thus are highly permeable for both thermal waters and gasses. The authors studied the central part of the steam field using a low-frequency seismic sounding method (LFS). The study beneath the thermal anomaly revealed: 1. a low-velocity bowl-shaped anomaly, which spreads to the depths of 250-300 m and correlates with the zone of hypergenesis of the modern hydrothermal system; 2. isolated anomalies at a depth of 3-5 km and deeper related to the zones with ruptured tectonic faults; 3. subvertical channels through which geothermal fluids comes up to the surface [Abkadyrov et al., 2015; Rychagov et al., 2018]. The revealed channels are rocks with higher crack-porous fluid permeability (and steam-and-gas mixture near the day-light surface) located within the zone of the deep fault [Abkadyrov et al., 2018]. Summarized geological data and integrated geological-geophysical investigation allow us to introduce a conceptual model of the structure of the Nizhne-Koshelevsky geothermal steam field. The investigation was supported by the Russian Foundation of Fundamental Research (grant 19-05-00102) and the Far East Branch of RAS.
|        Topic: Geophysics||Paper Number: 13034|