天然气水合物抑制过程中甲醇用量的影响

采用可视化高压流体测试装置,考察了甲醇含量对陕北某气田天然气水合物生成条件的影响。实验结果表明,气体组成对其水合物的生成条件有较大的影响,大分子气体或液态烃的存在可显著降低水合物的生成压力;甲醇含量对水合物生成的温度降有较大影响,甲醇含量越高,水合物生成温度降越大;水合物生成压力的对数(lgp)与温度(t_e)呈线性关系,不同甲醇含量时水合物生成条件的lgp～t_e曲线相互平行;甲醇质量分数小于30%时,Hammerschmidt方程和Nielsen-Bucklin方程对水合物生成温度降的预测偏差较小,但甲醇质量分数大于30%时,预测偏差较大;采用Nielsen-Bucklin修正式,预测甲醇用量的偏差小于2%。

Effect of Methanol Concentration on Control of Natural Gas Hydrate Formation

Hydrate formation conditions of methane, methane-cyclopentane and natural gas in water and methanol solution were investigated in a visual high-pressure cell. The simulated compositions of natural gas and salt solution were same as those from natural gas field. Hydrate formation condition varied with gas compositions in distilled water system. Presence of large molecular gas or liquid hydrocarbons could significantly reduce the hydrate formation pressure. In methanol inhibitor tests, methanol concentration influenced greatly temperature depression of hydrate formation. The relation of logarithmic pressure versus temperature of natural gas hydrate formation at a specific methanol concentration was correlated by a linear equation, and the lines corresponding to different methanol concentrations were parallel. Comparison of calculated and experimental gas hydrate formation temperature depressions showed that when methanol mass fraction was below 30% deviation of both Hammerschmidt and Nielsen-Bucklin equations in predicting temperature depression of hydrate formation were acceptable. However Nielsen-Bucklin equation was more preferable. But above 30%, both equations were unsatisfactory. A modified Nielsen-Bucklin equation was used to calculate the consumption of methanol in hydrate control process from North Shaanxi gas field. The deviation of the modified equation was less 2%.