| Abstract |
Supercritical geothermal (SG) fluids refer to those under the temperature and pressure condition exceeding the water critical point (Tc=373.946 ℃, Pc=22.064 MPa). The SG fluids possess the potential for enhanced productivity, which is closely associated with magma intrusion. At a depth of 2104 m in Krafla, Iceland, the IDDP-1 well encountered an active rhyolitic magma chamber. The natural state of such hydrothermal systems, particularly their thermal structure, exhibits significant heterogeneity determined by formation permeability. Quartz, as the most abundant mineral in the Earth’s crust, whose geochemical reaction parameters under equilibrium and kinetics mechanism fluctuate within the sub- to supercritical conditions (300~500oC), making the distribution of formation porosity and permeability hard to predict. Furthermore, substantial silica scaling was observed in IDDP-1, significantly impacting heat-extraction performance. Understanding quartz geochemical behavior during production is crucial for future SG development. In this study, we conducted water-quartz interaction experiments to determine the equilibrium constants and kinetics rate constants under the SG conditions. Compared to previous studies, our results show slightly higher solubility in the low-density area. The discrepancy can be attributed to the enhanced accuracy achieved through our adopted method of the vacuum in-situ sampling and rapid on-site testing that can bring higher accuracy. Furthermore, based on these data, we proposed a novel prediction model for quartz solubility. We also found that, the dissolution rate constant of quartz in water has similar fluctuation behavior with its solubility. Combined with these measured data, we have developed an innovative reactive transport modeling program that integrates multiphase flow, solute transport, and chemical behavior of quartz across steam/liquid and supercritical phases in various environments such as reservoirs and wellbores. The fluid properties are described using the IAPWS-IF97 equation of state (EoS). All functions can be accelerated in OpenMP mode, while the matrix solving efficiency is enhanced by introducing the Paridso solver. We applied the modeling program to analyze the IDDP-1 and constructed a 2-D wellbore-reservoir coupled model, with the objective of attaining a more profound comprehension of hydrogeological conditions at Krafla and the dissolution/precipitation pattern of quartz during drilling and testing phases. These findings offer valuable insights into the maximum potential within the IDDP-1 area, facilitating a preliminary understanding of quartz geochemical behavior in supercritical geothermal well development. |