The Soultz-sous-Forêts geothermal reservoir (France)—in particular, the GPK-4 well—has been proposed as a target for chemical stimulation under the DESTRESS Horizon-2020 framework. With a combination of batch reaction tests and acid flow-through experiments using hydrochloric acid (HCl) at different molarities and temperatures, we investigate the potential for acid-induced permeability enhancement of a granite analogous to the Soultz-sous-Forêts reservoir rock, by means of acid stimulation. In the batch reaction experiments, we find that the propensity for increase or decrease in porosity and permeability depends on the physico-chemical properties of the starting material: unaltered granite underwent a significant increase in both porosity and permeability relative to its initial state, altered granite exhibited a moderate increase in both porosity and permeability (modulated slightly by HCl molarity), whereas initially more porous and permeable thermally and naturally fractured granite exhibited an increase in porosity accompanied by a relative decrease in permeability. The extent to which permeability increased or decreased appears to be tied to the initial fluid-flow characteristics of the material. Using a new, custom-built acid permeameter, flow-through tests were performed on unaltered granite, while the acid was sampled at regular time intervals. Element release into solution recorded throughout the experiments, indicated dissolution of granite minerals. Despite this operative micromechanism, however, the absolute change in sample permeability is limited, both at room temperature and at $$100\, ^{\circ } \hbox {C}$$. Ultimately, these data suggest that the potential for geothermal reservoir enhancement using HCl is low at Soultz-sous-Forêts. Nevertheless, the possibility remains that a more targeted thermal or chemical stimulation approach—or hybrid thereof—could prove effective in the future.

中文翻译：

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实验性化学增产过程中花岗岩的物理性质演化

在DESTRESS Horizo​​n-2020框架下，有人建议将Soultz-sous-Forêts地热储层（法国）特别是GPK-4井作为化学增产的目标。通过分批反应测试和在不同摩尔浓度和温度下使用盐酸（HCl）进行酸流通实验的组合，我们研究了类似于Soultz-sous-Forêts储层岩石的酸诱导花岗岩渗透性增强的潜力，方法是：酸刺激的手段。在分批反应实验中，我们发现孔隙率和渗透率增加或降低的倾向取决于原材料的物理化学性质：未改变的花岗岩相对于其初始状态，孔隙率和渗透率均显着增加，改变后的花岗岩显示出孔隙度和渗透率均适度增加（受HCl摩尔浓度的调节），而最初具有更多孔隙和渗透性的热和自然破裂的花岗岩显示出孔隙度增加，同时渗透率相对降低。渗透率增加或降低的程度似乎与材料的初始流体流动特性有关。使用新的，定制的酸渗透仪，对未改变的花岗岩进行了流通测试，同时以固定的时间间隔对酸进行了采样。在整个实验中记录的元素释放到溶液中，表明花岗岩矿物溶解。尽管具有这种可操作的微机制，但是在室温和在$ 100 \，^ {\ circ} \ hbox {C} $$下，样品渗透率的绝对变化都受到限制。最终，这些数据表明在Soultz-sous-Forêts使用HCl增强地热储层的潜力很低。尽管如此，仍有可能在将来证明更有针对性的热刺激或化学刺激方法（或其混合方法）有效。