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<p>Sustainable management of produced water in arid regions requires balancing industrial reuse with protection of finite groundwater resources. This study investigates the physicochemical and microbial drivers of water quality deterioration in a produced water reinjection system within Egypt’s Abu Gharadig Basin and evaluates the associated risks to the adjacent Moghra aquifer. Produced water from four injection wells, sampled monthly over 7&#xa0;months, was hypersaline (TDS range 26,800–35,500&#xa0;mg/L) and contained elevated sulfate-reducing bacteria (mesophilic SRB at 10<sup>3</sup>&#xa0;CFU/mL). Thermodynamic modelling (SoftPitzer™) and X-ray diffraction confirmed severe calcium carbonate scaling (saturation index = 2.71 at reservoir conditions; 70&#xa0;wt% CaCO<sub>3</sub> in downhole deposits). Water-quality degradation reduced injection system capacity from 668 to 289&#xa0;m<sup>3</sup>/d over 7&#xa0;months (57% decline), necessitating the diversion of excess produced water to unlined surface disposal lagoons. Voidage replacement ratio data were unavailable; however, the 57% injectivity decline was measured directly at the wellhead, confirming that water-quality-driven impairment—rather than reservoir pressure depletion alone—necessitated the diversion of produced water to unlined lagoons. Fourteen years of groundwater monitoring (2011–2024) across three downgradient wells (W2, W3, W5) provided evidence strongly consistent with industrial salinization originating from lagoon seepage: groundwater salinity rose from a natural background of approximately 3500–35,113&#xa0;mg/L by 2024, accompanied by water-level declines of up to 0.9&#xa0;m. While the spatial salinity gradient and temporal trends are compelling, definitive source attribution awaits isotopic confirmation (δ<sup>18</sup>O, δ<sup>2</sup>H). Qualitative field-based diagnostic thresholds are proposed: when the calcite saturation index exceeded 2.0 and mesophilic SRB populations exceeded 10<sup>2</sup>&#xa0;CFU/mL in this untreated system, injectivity losses greater than 50% were observed within approximately 6&#xa0;months. These thresholds are preliminary and require independent validation. Optimizing produced water quality prior to reinjection is both an operational necessity and an environmental imperative. Effective treatment—including scale inhibition, biocide application, and solids removal supports a circular water economy, reduces the risk of irreversible aquifer salinization, and contributes to the objectives of UN Sustainable Development Goal 6 (Clean Water and Sanitation).</p>

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Aquifer salinization driven by untreated produced water reinjection is mediated by mineral scaling and microbial corrosion in the Abu Gharadig Basin Egypt

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月8日

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  • Aref Adel Abd Algaliel,
  • Mohamed K. Fattah,
  • Ezzat A. El Fadaly,
  • Salah Elsayed,
  • Mostafa Gamal Hegab,
  • Mahmoud F. Mubarak

摘要

Sustainable management of produced water in arid regions requires balancing industrial reuse with protection of finite groundwater resources. This study investigates the physicochemical and microbial drivers of water quality deterioration in a produced water reinjection system within Egypt’s Abu Gharadig Basin and evaluates the associated risks to the adjacent Moghra aquifer. Produced water from four injection wells, sampled monthly over 7 months, was hypersaline (TDS range 26,800–35,500 mg/L) and contained elevated sulfate-reducing bacteria (mesophilic SRB at 103 CFU/mL). Thermodynamic modelling (SoftPitzer™) and X-ray diffraction confirmed severe calcium carbonate scaling (saturation index = 2.71 at reservoir conditions; 70 wt% CaCO3 in downhole deposits). Water-quality degradation reduced injection system capacity from 668 to 289 m3/d over 7 months (57% decline), necessitating the diversion of excess produced water to unlined surface disposal lagoons. Voidage replacement ratio data were unavailable; however, the 57% injectivity decline was measured directly at the wellhead, confirming that water-quality-driven impairment—rather than reservoir pressure depletion alone—necessitated the diversion of produced water to unlined lagoons. Fourteen years of groundwater monitoring (2011–2024) across three downgradient wells (W2, W3, W5) provided evidence strongly consistent with industrial salinization originating from lagoon seepage: groundwater salinity rose from a natural background of approximately 3500–35,113 mg/L by 2024, accompanied by water-level declines of up to 0.9 m. While the spatial salinity gradient and temporal trends are compelling, definitive source attribution awaits isotopic confirmation (δ18O, δ2H). Qualitative field-based diagnostic thresholds are proposed: when the calcite saturation index exceeded 2.0 and mesophilic SRB populations exceeded 102 CFU/mL in this untreated system, injectivity losses greater than 50% were observed within approximately 6 months. These thresholds are preliminary and require independent validation. Optimizing produced water quality prior to reinjection is both an operational necessity and an environmental imperative. Effective treatment—including scale inhibition, biocide application, and solids removal supports a circular water economy, reduces the risk of irreversible aquifer salinization, and contributes to the objectives of UN Sustainable Development Goal 6 (Clean Water and Sanitation).