Investigation on coupling deposition and plugging of hydrate and wax in gas–liquid annular flow: Experiments and mechanism

Abstract

The coupling deposition and plugging caused by hydrate formation and wax precipitation during the development of deep water natural gas resources bring new industrial challenges and theoretical difficulty. We designed a single-pass pipeline with two types to investigate deposition behavior and systematically performed the coupling deposition and plugging of hydrate and wax experiments in gas–liquid annular flow. The experimental results illustrate that the single solid phase of hydrate is covered layer sheet deposition, while the coupling solid phase of hydrate and wax is bulk aggregations arch bridge deposition. Meanwhile, the natural eddy zone in reducing pipeline accelerates coupling solid particles deposition. Our finds provided the first knowledge on the double effect that wax crystals inhibit particles adhesion and gel network increases aggregations arch bridge blockage. For the low water content in emulsion system, the gel network provides gathering place for hydrate particles, and the arch bridge structure formed by aggregations accelerates the pipeline blockage. The plugging time is shortened by up to 72.6% with the wax concentration increase from 0 wt% to 3 wt%. For the high water content in emulsion system, the majority of wax crystals adsorbed on the hydrate particles and reduce particles cohesion force, which increase the plugging time. Combined with the microscopic morphology evolution perspective of hydrate particles coupled wax, the coupling deposition of hydrate and wax in gas–liquid annular flow has four stages: gas–liquid flow, coupling solid phase formation, coupling solid phase deposition and sloughing, and coupling solid phase plugging. This study can provide theoretical support and design basis for flow assurance program of deep water gas fields and low temperature natural gas transportation pipelines.