Abstract: Plugging of oil and gas wellbores, pipelines and equipment caused by natural gas hydrates is a major problem in the oil and gas industry and the resulting production reductions or interruptions cut into profits and bring about high costs for plug removal. In view of the lack of an accurate and reliable computational model and experimental data of plug removal by an autogenous pyrolysis plugging agent, a new mathematical model of the hydrates removal process by autogenous pyrolysis plugging agent has been established based on hydrate phase equilibrium thermodynamics and decomposition kinetics, including energy model and mass model of the hydrates removal process. The model is solved by numerical simulation. On this basis, the paper investigates the plug removal process and parameter variation laws in the pure autogenous heat system, autogenous heat system with electrolytes (salt)and autogenous heat system, respectively; based on the experimental results, the relationship among the plug removal agent dosage and concentration and removal time in the unplugging process of two agents with different concentrations and heat generation peaks have been calculated and analyzed. The results are shown as follows. (1)The calculated values of the mathematical model are in good agreement with the experimental values, indicating that the model can better calculate and analyze the blockage of hydrates and unplugging process by plug removal agent under different working conditions. (2)With the increasing of the heating temperature of autogenous pyrolysis plugging agent, the concentration of both the sodium and magnesium ions and the methanol and diethylene glycol in the agent, the decomposition rate of hydrates increases and the unplugging time decreases; when the heating temperature is less than 295 K, the system containing magnesium ions and diethylene glycol ions has a significant effect on the decomposition of hydrates. (3)The model-based plug removal agent filling amount and unplugging time demonstrates that the effect of plug removal agent is closely related to the peak heat generation, composition and concentration of the agent, and the unplugging effect of the agent used in the experiment can meet the demands on the engineering site. Under the same conditions, the effect of the ammonium salt and nitrite autogenous heat system is better than that of the polyhydroxy aldehyde autogenous heat system. The results show that the autogenous pyrolysis plugging agent of high temperature heating system can be developed during hydrates removal, and the unplugging effect can be enhanced by adding appropriate concentrations of electrolytes and alcohols without changing the heating properties of the original unplugging agent, which can achieve rapid removal of hydrates and prevent the secondary generation of hydrate.

Key words: autogenous pyrolysis plugging agent, natural gas hydrate, heat balance, decomposition, mathematical model

摘要： 天然气水合物造成的油气井筒、管道和设备堵塞是石油天然气行业的一个重要问题,其会导致减产或生产中断,之后进行的解堵作业将进一步增加油田生产成本。针对目前缺乏准确可靠的自生热解堵剂解堵计算模型和实验数据的问题,建立了一种新的水合物自生热解堵剂解堵过程数学模型,该模型基于水合物相平衡热力学和分解动力学建立,包括水合物解堵过程的能量模型和质量模型;通过数值模拟进行了模型的求解,分别研究了纯自生热体系、含电解质(盐)自生热体系和含醇自生热体系解堵剂解堵过程及参数变化规律;基于实验结果,计算并分析了不同浓度和发热峰值的两种解堵剂解堵过程解堵时间、解堵剂用量与解堵剂浓度关系。研究结果表明:①该数学模型计算值与实验值吻合度高,能较好地计算并分析不同工况水合物堵塞及解堵剂解堵情况;②随自生热解堵剂发热温度、解堵剂中钠和镁离子浓度以及解堵剂中甲醇和二甘醇浓度的增加,水合物分解速率增加、解堵时间减少,发热温度小于295 K、含镁离子和二甘醇离子体系对水合物分解过程影响更大;③基于所建立模型绘制的解堵剂加注量及解堵时间图版表明,解堵剂的解堵效果与解堵剂发热峰值、成分、浓度等关系密切,实验所用解堵剂解堵效果均能满足工程现场需求,相同条件下铵盐与亚硝酸盐自生热体系解堵剂作用效果优于多羟基醛自生热体系解堵剂。在水合物解堵作业中配置高温发热体系的自生热解堵剂,并在不改变原有解堵剂发热性质的前提下添加适当浓度的电解质及醇类物质增强解堵效果,可实现水合物的快速清除并防止水合物的二次生成。

关键词: 自生热解堵剂, 天然气水合物, 热量平衡, 分解, 数学模型