产水气井碳酸钙阻垢剂分子模拟研究

Molecular Simulation Research on Calcium Carbonate Scale Inhibitor for Water-producing Gas Wells

为了解决西南油气田分公司磨溪气田龙王庙组地层水矿化度高、结垢离子多导致油管经常发生碳酸钙结垢堵塞的问题,采用分子动力学模拟阻垢剂与钙离子和碳酸根离子相互作用过程,分析阻垢剂阻止碳酸钙垢的机理。在不同温度条件下分别模拟了水溶液中三聚磷酸钠和羧甲基葡聚糖阻垢剂阻止钙离子与碳酸根离子生成碳酸钙垢的过程,明确了阻垢剂与结垢离子的作用方式、阻止机理。分子模拟结果表明:碳酸钙垢的生成主要以钙离子或碳酸根离子为中心,钙离子与碳酸根离子相互吸引,当结垢阴阳离子距离达到0.25 nm后就会生成碳酸钙分子,碳酸钙分子不断聚集形成晶体,温度越高越容易结垢;阻垢剂的阻垢机理是阻垢剂的阴离子对钙离子吸引力更大,从碳酸根离子与钙离子在距离为0.25 nm的结合概率降低可以得到证明,溶液中阻垢剂阴离子之间相互排斥,垢分子与离子相对分散,碳酸钙无法聚集形成晶体;三聚磷酸钠阻垢剂的阻垢效果比羧甲基葡聚糖(CMD)阻垢剂更好,温度越高垢分子的生成概率越低,三聚磷酸钠最大概率密度比羧甲基葡聚糖(CMD)阻垢剂的小0.415倍;三聚磷酸钠阻垢剂阴离子负价高,相互排斥,造成溶液中所有阴阳离子更分散,垢分子难以聚集形成碳酸钙晶体;采用该分子模拟方法可以筛选适合的阻垢剂。

In order to solve the problem of calcium carbonate scaling and blockage in the tubing caused by high salinity and many scaling ions in the formation water of the Longwangmiao Formation in Moxi Gas Field of Southwest Oil and Gas Field Branch.Using molecular dynamics simulation to investigate the effect of scale inhibitors on the formation of calcium carbonate scale by combining calcium ions and carbonate ions.To analyze the mechanism of scale inhibitors to inhibit the formation of calcium carbonate scale.Simulating the process of sodium tripolyphosphate and carboxymethyl dextran scale inhibitors in aqueous solution with calcium ions and carbonate ions under different temperature conditions to clarify the action mode and inhibition mechanism of scale inhibitors and scaling ions.The molecular simulation results show that the formation of calcium carbonate scale is mainly centered on calcium ions or carbonate ions.When the distance between cationic and anionic scaling ions reaches 0.25 nm,calcium carbonate molecules are generated.Calcium carbonate molecules continue to aggregate to form crystals,and the higher the temperature,the easier it is to scale.The scale-inhibiting mechanism of scale inhibitors is that the anions of scale inhibitors have greater attraction to calcium ions.This can be proved by the fact that the binding probability of carbonate ions and calcium ions at a distance of 0.25 nm is reduced.In solution,the anions of scale inhibitors repel each other,the scaling molecules and ions are relatively scattered,and calcium carbonate can not aggregate to form crystals.The scale-inhibiting effect of sodium tripolyphosphate scale inhibitors is better than that of carboxymethyl dextrin(CMD)scale inhibitors.The higher the temperature,the lower the probability of generating scaling molecules.The maximum probability density of sodium tripolyphosphate is 0.415 times smaller than that of carboxymethyl dextrin(CMD)scale inhibitors.The anions of sodium tripolyphosphate have high negative charges and repel each other,making all cations and anions in solution more scattered.It is difficult for scaling molecules to aggregate to form calcium carbonate crystals.This molecular simulation method can be used to screen suitable scale inhibitors.