Potential kinetic effects of wax on clathrate hydrate formation: A review

Waxes and hydrates may coexist in oil-gas-water multiphase mixed transport pipelines. They all occur at low temperatures and may have kinetic influences mutually. The impact of waxes on hydrates has been a topic of considerable discussion, yet a consensus has not been reached. Recently published studies have compiled and found that the uncertainty may be attributed to the inherent complexity of oil-water mixtures. Consequently, the impact of waxes on the entirety of the hydrate formation process in the presence/absence of emulsifiers is deliberated, and the effect of emulsifiers on hydrate formation in the presence of waxes is discussed by comparison. The wax on hydrate nucleation is discussed by analyzing the induction period, the microstructure of emulsion and hydrate. The growth and aggregation properties are inferred by gas transformation, adhesion forces, and rheological properties. Further, the effect of waxes on hydrate formation is discussed at the molecular scale. The results show that waxes have a negative effect on the whole process of hydrate formation under the stable W/O emulsion system. In contrast, waxes have a promoting effect on hydrate formation in the O/W emulsion system under high-content conditions. The impact of waxes on hydrate formation remained uncertain in the absence of emulsifiers due to the disordered distribution of oil and water when no emulsifier was present. Eight potential forms of wax crystals in oil-water mixtures are summarized, and their influence on hydrate formation is discussed. The coexistence of multiple forms of wax will lead to complex results in terms of the effect of wax on hydrates. Existing research's shortcomings and challenges are emphasized, which can be expected to allow rapid development of this direction.