Outcrop analogue constraints on subsurface reservoir properties of the Puga geothermal field, NW Himalaya

Abstract

There has been a large barrier in geothermal energy production in India due to the knowledge gap in understanding the subsurface uncertainties. In Puga, Ladakh, a significant amount of research has been done that estimates the availability of >5000 MWh of geothermal energy, but it remains untapped. It is largely due to a limited understanding of reservoir characteristics. In addition to the comprehensive review of literature, this study includes outcrop analogue studies to develop a better understanding of the subsurface geothermal system. Observing the geological settings, the lithologies and structures exposed in the cliffs adjacent to Puga valley are analogous to the subsurface, to depths of at least a few kilometres. A 3-D model of the outcrop is developed from aerial imagery collected using drone (quadcopter), that has been utilized to interpret fracture sets and foliation planes. Areas with intensely developed fabrics demonstrate the mechanical significance of these fabrics. The distinctive relationship between faults in the outcrop and the valley fill provides evidence for recent movement on the faults. Further, a variety of mineral fillings were observed in fractures across the outcrop which includes quartz±tourmaline veins, hydrothermal biotite, vuggy sub- and euhedral quartz, finegrained iron oxides and iron-rich travertine. Several exposures near the base of the cliffs show clear advanced argillic and sulfuric alteration. This study integrates digital outcrop mapping techniques along with constraints provided by the literature to derive a conceptual model of the Puga geothermal system. It provides an understanding of the structural architecture of the reservoir, which is an important parameter in developing the ‘Integrated reservoir model’.