Hydrate Management in Deadlegs: Effect of Header Temperature on Hydrate Deposition

Abstract

Deadlegs in oil and gas production systems often encounter hydrate plugs by deposition. Temperature is generally known to be an important variable in hydrate formation, but the effects in deadlegs are not exactly known. This study focuses on the effects of the header temperature on the hydrate deposition in gas-filled vertical deadlegs at constant wall temperature. All experiments are conducted with a methane/ethane gas mixture at constant pressure. The pipe wall temperature is kept constant while considering different header temperatures. The tests show that the header temperature has a significant impact in the hydrate deposit growth rate and distribution in the deadleg. It is also found that the hydrate deposit can, in turn, change the temperature field inside the pipe. The header temperature or the pipe temperature field can be used to estimate the hydrate distribution in the deadleg. Under the right conditions, hydrates can form a restriction in the deadleg and its location is usually close to the boundary of a hydrate-stable region. The location of the restriction can be correlated to the header temperature. At 80 °C, the location is estimated to be 15−18 ID, and at 30 °C, the location is estimated to be 9−12 ID. The results of this study contribute to the understanding of the hydrate deposition mechanism in deadlegs.

A Multiscale Approach for Gas Hydrates Considering Structure, Agglomeration, and Transportability under Multiphase Flow Conditions: I. Phenomenological Model

“…Large interfaces happen mostly in stratified, intermittent (in the elongated bodies), and free-phase flows. In cases of large interfaces where the gas is the predominant phase at the bulk (e.g., annular flow), the particles grow directly over the wall as a deposit ,− and a slurry flow will not be present. In smaller interfaces, the hydrates are considered to quickly encompass the entire drops/droplets.…”

Hydrate Management in Deadlegs: Effect of Natural Convection on Hydrate Deposition

“…By using a 3 in. deadleg, Zhang et al studied the effect of header temperature on hydrate deposition in deadlegs. The experimental results showed that the header temperature has an important impact on the growth rate and distribution of the hydrate deposits, which in turn also impacted the temperature field in the deadleg.…”

Hydrate Management in Deadlegs: Effect of Pipe Size on Hydrate Deposition

“…The data in Figure 3a,b are from experiments 1−1 and 4−1, respectively. In all our studies, including our previous ones, 12,13 three types of temperature profiles have been observed: (i) when the temperature is significantly lower than the HET (e.g., by 10 °C), the temperature only slightly increases at the hydrate onset and then gradually decreases until a steady-state value (section 3 in Figure 3d); (ii) when the temperature is close to the HET, it increases initially, but then fluctuates (section 4 in Figure 3d); and (iii) when the temperature is above the HET, it increases rapidly at the beginning and reaches a steady constant value (section 5 in Figure 3d). The three patterns occur from the low to the high temperature region.…”

“…The cause of such phenomena is hydrate deposition in the pipe and has been discussed in detail in our previous papers. 12,13 Besides, the rates of the temperature change vary at different conditions. In the system with a larger ID, the change is generally slower.…”

“…deadlegs have been studied. 12,13 The condensation was also studied using permittivity sensors at various temperature conditions in a 1-in. deadleg.…”