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(56s) Production Challenges of Gas Hydrates in Flowlines

Authors: 
Zhang, X., Colorado School of Mines
Hydrates are a common challenge in the oil and gas production. They are solids forming from small gas and water molecules. Hydrate formation usually requires high pressure and low temperature. The hydrate formation is undirable as it can lead to production interuption and financial loss. The production systems, on the other hand, are always complex with different sections and pipe networks. Different parts of the hydracarbon flowlines are found to face different hydrate challenges.

One common component of the production systems is the gas-filled sections with no through-flow, so called deadlegs. The fluids within the deadlegs are relatively stagnant comparing to the main flowline. If in a cold environment and not properly insulated, the fluids within a deadleg can become so cold that hydrates can form. The field operation showed that deadlegs often encounter hydrate deposition but the understanding was very limited. The risks and the mechanism had not been well studied or publicly available. Therefore, we collaborated with Equior to conduct a systematic study to understand the hydrate deposition in deadlegs. We characterized the hydrate deposition process, quantified the effect of different variables, and modeled the process using transport equations.

The main flowline with flowing fluids can also encounter hydrate problems. However, current experimental setups for hydrates are either very costly to generate flow (e.g. flowloops) or cannot generate flow (e.g. autoclaves). Therefore, we collaborated with Total and DeepStar and developed a new bench-scale setup, named rock-flow cell, to generate flow and study hydrate phenomena under flowing conditions. We characterized the capability of the system by testing different water cuts and liquid loadings. The visual observation from the radial and the axial directions provided rich information to improve the understanding in the hydrate formation process. We also utilized the system to evaluate the performances of various anti-agglomerants. The setup provided satisfactory results to rank the chemicals with the direction observation.

In summary, we have collaborated the industry partners to spend systematic efforts to understand the hydrate problems in flowlines. Our achievement has improved the understanding in the hydrate flow assurance challenges and helped determine the hydrate management strategies.

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