气提法处理高含CO_2油田采出水的试验研究

Experimental study of high CO_2 concentration oilfield produced water treatment using gas stripping method

气驱油田采出水中大量CO_2的存在导致采出水腐蚀性增强,且造成水中悬浮物浓度增大,影响回注或排放。试验研究了含不同CO_2浓度的采出水中p H值、腐蚀速率、含油量和离子浓度等水质特性参数的变化,考察了气液比、含油量及温度等因素对气提法处理油田采出水中CO_2效果的影响。结果表明:CO_2浓度是影响油田采出水p H值、离子浓度及腐蚀速率等水质特性参数变化的重要因素;气提法去除采出水中CO_2的效果明显,升高温度、降低含油量均有利于提高污水中CO_2去除率;此外,与空气气提相比,氮气气提更有利于降低含油污水的腐蚀速率。在40℃和常压下,氮气气提44 min即可使污水p H值升高到7以上,碳钢腐蚀速率降至0.076 mm/a以下;当以氮气为载气,气液比为26∶1,温度为40℃时,含油污水中CO_2去除率可达100%,气提处理效果最佳。

The existing of high concentration CO2 in gas-controlled oilfield produced water may strengthen the corrosivity and aggrandize the suspended solids concentration of the produced water, which has an adverse impact on effluent water reinjection or discharge. The test simulated the variation of pH value, corrosion rate, oil content, ion concentration and some other indexes in the produced water with different CO2 concentrations, and then, the impact of factors such as gas-liquid ratio, oil content, temperature, etc., on CO2 removal from oilfield produced water were investigated. The results showed that, CO2 concentration was the main factor influencing pH value, ion concentration, corrosion rate and some other characteristic parameters of the oilfield produced water, and it could be effectively removed by gas stripping method, the removal rate increased with the increasing of temperature and the decreasing of oil content. Besides, compared to air stripping, nitrogen stripping was more conducive to corrosion rate decreasing of oily sewage. Under ordinary pressure at 40 ℃, 44 min of nitrogen stripping could raise the pH value of the sewage to above 7 and decrease the corrosion rate of carbon steel to be- low 0.076 mn/a. Using nitrogen as the carrier gas, the optimal gas stripping effect could be obtained at 40 with gas-liquid ratio of 26 ： 1, the removal rate of CO2 in the oily sewage reached 100%.