天然气水合物化学试剂-CO2置换开采实验研究与认识

Experimental study and recognition of natural gas hydrate chemical reagent - CO2 exploitation

Abstract

为了解决CO2置换法开采天然气水合物过程中出现的置换速度慢、置换效率低等问题，提出了化学试剂-CO2置换结合开采试验的措施。实验表明：（1）甲醇溶液分解水合物的过程大致可以分为以下三个阶段：快速分解初始阶段、水合物分解与稳定转变的竞相作用阶段和分解稳定阶段。通过实验模拟得出，地层压力直接影响到甲醇试剂对水合物的分解能力，改变地层压力能够提高CH4水合物开采速率。（2）基于甲醇试剂+CO2置换开采方法可获较高的水合物分解率。在甲醇试剂作用，后续注入的CO2仍然促进了CH4分解即基于甲醇试剂分解水合物后进行CO2水合物的置换开采是可行的。研究成果对天然气水合物化学试剂法矿场试采具有重要的意义。In order to solve the problems of slow replacement rate and low degree of substitution in the process of CO2 displacement by natural gas hydrate, a method of chemical reagent-CO2 displacement combined mining experiment was proposed. Taking the thermodynamic methanol inhibitor as an example, three groups of experiments were carried out: critical temperature pressure condition for CH4 decomposition at different methanol concentrations, CH4 hydrate decomposition under the condition of methanol reagent at 30% concentration, and methanol reagent-CO2 combined mining. Experiments show that: (1) The concentration of methanol plays a decisive role in hydrate recovery. Methanol reagent has the property of highly reducing the formation temperature of hydrate. Methanol solution concentration is positively correlated with the critical temperature drop of hydrate decomposition and formation pressure. (2) The methanol solution decomposition of hydrate can be roughly divided into three stages: the initial stage of rapid decomposition, the competitive stage of hydrate decomposition and stable transformation, and the stable stage of decomposition. Through experimental simulation, it is concluded that formation pressure is a direct factor affecting the decomposition ability of methanol reagent to hydrate. By changing formation pressure, the rate of CH4 hydrate recovery can be improved. (3) A higher hydrate decomposition rate can be obtained based on the methanol reagent-CO2 displacement mining method. In the action of the methanol reagent, the subsequent injection of CO2 still promotes the decomposition of CH4, that is, the displacement of CO2 hydrate after the decomposition of the hydrate based on the methanol reagent is feasible. The research results are of great significance especially for large-scale mine test mining of permafrost natural gas hydrate chemical reagent method.