ABSTRACT

Acidic fracturing flowback fluid (AFFF) has the characteristics of low pH value, high chemical oxygen demand (COD), high corrosiveness and complex components. Surface discharge without treatment may contaminate the environment. However, wastewater treatment after centralized transportation has potential safety risks and requires high costs. In this study, we confirmed that calcium and magnesium could affect cross-linking property of fracturing fluid prepared by flowback fluid, and conducted a three-step process, two-stage filtration, chemical precipitation, and flocculation precipitation, on AFFF. After treatment, we made new hydraulic fracturing fluid using the treated acidic flowback fluid as base fluid and compared the quality of the new hydraulic fracturing fluid to the ones used freshwater as base fluid. The results showed when concentration of sodium carbonate, polyaluminium chloride (PAC), polyacrylamide (PAM) were 145, 1000, and 20 mg/L respectively, the treatment result was optimal. After treatment, the oil content of AFFF decreased from 7400 to 26.53 mg/L and suspended solids (SS) from 650 to 18.24 mg/L, and the removal rate of high-valence metal ions was more than 99%. The rheological properties and viscoelasticity of new fracturing fluid prepared by the treated AFFF were similar to the ones prepared by freshwater, which met the requirements of high temperature and shear resistance for ultra-deep wells.

摘要

酸性压裂返排液（AFFF）具有pH值低、化学需氧量（COD）高、腐蚀性强、成分复杂等特点。未经处理的表面放电可能会污染环境。但集中运输后的废水处理存在安全隐患，成本高。在本研究中，我们证实了钙和镁对返排液制备的压裂液的交联性有影响，并对AFFF进行了两级过滤、化学沉淀和絮凝沉淀三步工艺。处理后，我们以处理后的酸性返排液为基液制备了新的水力压裂液，并将新水力压裂液的质量与淡水为基液的压裂液质量进行了比较。结果表明，当碳酸钠、聚合氯化铝（PAC）、聚丙烯酰胺（PAM）的浓度分别为145、1000和20 mg/L时，处理效果最佳。处理后，AFFF含油量由7400下降至26.53 mg/L，悬浮物（SS）由650下降至18.24 mg/L，高价金属离子去除率达99%以上。经处理的AFFF制备的新型压裂液的流变性和粘弹性与淡水制备的相似，满足超深井的高温抗剪要求。53 mg/L，悬浮物（SS）从650到18.24 mg/L，高价金属离子去除率达99%以上。经处理后的AFFF制备的新型压裂液的流变性和粘弹性与淡水制备的相似，满足超深井的高温抗剪要求。53 mg/L，悬浮物（SS）从650到18.24 mg/L，高价金属离子去除率达99%以上。经处理的AFFF制备的新型压裂液的流变性和粘弹性与淡水制备的相似，满足超深井的高温抗剪要求。