A hydraulic stimulation was carried out on a granodiorite reservoir in an enhanced geothermal system in August 2017 in Pohang, Korea. Water injected into the 4.2 km deep PX-1 well contained c. 330−360 mg/L sulphate, with a negative δ³⁴S. The resulting flowback water became more saline with time, with sulphate and chloride concentrations and dissolved sulphate δ³⁴S all increasing. Compared with conservative advective-dispersive and mixing models, the flowback contained surplus sulphate with an elevated δ³⁴S. The PX-1 reservoir fluid is saturated with respect to anhydrite at downhole temperatures and pressures. Dissolution by injected surface water of secondary anhydrite along fracture surfaces, most likely with elevated δ³⁴S reflecting the reservoir fluid, is likely to have resulted in an excess of ³⁴S-enriched sulphate in the flowback fluid. An alternative hypothesis involving oxidation of pyrite is also plausible but is stoichiometrically inadequate to account for the observed sulphate excess, and unlikely from a sulphur isotopic perspective. This analysis thus contributes to the evidence for water-rock reactions during stimulation of the Pohang granodiorite.

2017年8月，在韩国浦项市对一个增强地热系统的花岗闪长岩储层进行了水力压裂。注入4.2公里深的PX-1井的水包含c。330-360毫克/升的硫酸，具有负δ ³⁴ S.将所得回流水变得更加盐水与时间，用硫酸盐和氯化物的浓度和溶解的硫酸盐δ ³⁴ S总增加。保守平流分散和混合模型相比，该回流包含剩余硫酸盐与升高δ ³⁴ S的PX-1储液器流体相对于饱和在井下的温度和压力，以硬石膏。通过沿断裂面次级硬石膏的注入表面水溶解，最有可能与升高的δ ³⁴反映储层流体的硫很可能导致返排液中过量富集³⁴ S的硫酸盐。涉及黄铁矿氧化的另一种假设也是合理的，但在化学计量上不足以解释所观察到的硫酸盐过量，并且从硫同位素的角度来看不太可能。因此，该分析为浦项花岗闪长岩增产过程中的水-岩反应提供了证据。