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