Harsh subsurface conditions pose a widespread challenge for permanently plugging and abandoning (P&A) oil and gas wells. A new, cement-free plugging material is proposed and demonstrated using Nature-inspired geochemical processes to generate stable and resilient, rock-like material that is ideally suited to acidic geofluid, high-pressure, and high-temperature (AG-HP-HT) conditions. These conditions accelerate hydration and carbonation reactions that turn granular ultramafic raw materials into competent rock, dubbed here as “Geologically Activated Cement” (GAC). The experiments firstly demonstrate the generation of GAC in an acidic environment, using a pressure of 13.7 MPa and temperature of 180 °C as typical representative values relevant to P&A operations in high temperature reservoirs. The results show that within hours to days, and hence relevant to P&A operational timeframes, a solid, rock-like material can be produced from Mg₂SiO₄–CO₂ mixtures. The reaction products are analyzed by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS). These analysis shows the rock to be comprised of unreacted olivine particles that are bound together by magnesium carbonate. Because of the presence of unreactive olivine, the reaction is set in motion again by exposing the olivine to CO2-enriched fluid by thermally damaging (cracking) the sample. The damaged material is then subjected to flow-through of carbonic acid for 8–14 h. Under these conditions, GAC experiences a 75% reduction in permeability over the hours immediately following damage. Control experiments using class H cement experience steady to slightly increasing permeability under the same conditions and over a similar time frame. We therefore show that GAC can self-seal cracks within a few hours when subjected to damage and subsequent flow of acidic fluid under HPHT conditions. This self-sealing behavior provides the potential for a resilient cementing system over geological timescales.

恶劣的地下条件对永久堵塞和废弃 (P&A) 油气井提出了广泛的挑战。提出并证明了一种新的无水泥堵塞材料，它使用受自然启发的地球化学过程来生成稳定且有弹性的类岩石材料，非常适合酸性地质流体、高压和高温 (AG-HP-HT) ） 条件。这些条件加速了水化和碳化反应，将颗粒状超镁铁质原材料变成了有能力的岩石，这里被称为“地质活性水泥”(GAC)。实验首先展示了在酸性环境中生成 GAC，使用 13.7 MPa 的压力和 180 °C 的温度作为与高温油藏 P&A 操作相关的典型代表值。结果表明，在几小时到几天内，₂ SiO ₄ –CO ₂混合物。通过 X 射线粉末衍射 (XRD)、扫描电子显微镜 (SEM) 和能量色散 X 射线光谱 (EDS) 分析反应产物。这些分析表明岩石由未反应的橄榄石颗粒组成，这些颗粒被碳酸镁结合在一起。由于存在未反应的橄榄石，通过热破坏（裂解）样品将橄榄石暴露于富含 CO2 的流体，从而再次启动反应。然后将损坏的材料流过碳酸 8-14 小时。在这些条件下，GAC 在损坏后的数小时内渗透率会立即降低 75%。使用 H 级水泥的对照实验在相同条件下和类似时间范围内经历稳定到略微增加的渗透率。因此，我们表明，在 HPHT 条件下受到损坏和随后的酸性流体流动时，GAC 可以在几个小时内自行密封裂缝。这种自密封行为为地质时间尺度上的弹性固井系统提供了潜力。