Experimental study on hydrate anti-agglomerating performance of quaternary ammonium salt cationic surfactants

Abstract

[Objective] Hydrate plugging has become one of the significant challenges to the safe operation of deepwater oil and gas pipelines. Flowable hydrate slurry has been recognized as an effective solution to mitigate hydrate accumulation and plugging, enabling safe transmission of oil and gas. Therefore, the research and development of high-performance anti-agglomerants are crucial. [Methods] A self-designed rocking cell was employed to investigate the formation process of methane hydrate in white oil with a water content of 20%. The performance of hydrate anti-agglomerants was evaluated blindly in the autoclave. Thirteen quaternary ammonium cationic surfactants, including didodecyl hydroxypropyl ammonium chloride (DHAC) and dioctadecyl dimethyl ammonium chloride (DDAC), were tested to estimate their anti-agglomerating performance. Classification evaluation was conducted based on the slider displacement trajectory in the rocking cell recorded by the motion detector, using the slider’s movement range and velocity as criteria for classification into grades A, B, and C in descending order. [Results] Screening experiments identified five quaternary ammonium cationic surfactants in grade B and eight in grade C, without any in grade A among the 13 surfactants. Surfactants in grade C failed to prevent the plug of hydrates, but under their influence, the same anti-agglomerating process required more hydrates, so they, in a level, assist to slow down the formation of hydrate plug. Further comparison among the five grade B specimens, based on the slider’s final movement velocity both forward and backward, revealed the following descending order of anti-agglomerating performance: DHAC, GQA31745, HEIMQA, CGHDAC, and UITS. [Conclusion] Cationic surfactants demonstrate the ability to disperse and inhibit the agglomeration of hydrate crystals in oil and gas pipelines. Cationic drilling fluid additives such as DHAC hold potential as effective hydrate anti-agglomerants. This study presents a novel idea for prevention and control of hydrates in oil and gas pipelines.

Keywords

• oil and gas pipeline
• quaternary ammonium salt
• surfactant
• hydrate
• anti-agglomerating