A Wet Cold-Flow Technology for Tackling Offshore Flow-Assurance Problems

Abstract

Summary Flow assurance is a major challenge in offshore and deepwater operations. Conventional approaches for preventing gas-hydrate formation involve using thermodynamic inhibitors (e.g., methanol, glycol) or kinetic hydrate inhibitors or operating outside the hydrate- stability zone by insulating the pipeline and/or active heating. These techniques are not always economical and in some cases are not practical for deepwater operations, long tiebacks, or aging reservoirs with high water cuts. The industry needs new and novel flow-assurance techniques to address these challenging conditions. The approach presented in this paper is a wet cold-flow-based method in which gas-hydrate management rather than prevention is the goal. The HYDRAFLOW concept is to allow/encourage gas-hydrate formation, but prevent agglomeration in the pipeline and thus avoid blockage. The idea is to convert most of the gas phase into hydrates and transfer it in the form of hydrate-slurry in the pipeline. Where produced water is insufficient for maximum hydrate formation, excess water can be added from other sources such as seawater (hence wet cold flow, because the presence of a free aqueous phase is desired). It is also possible to adjust the hydrate-slurry viscosity by adjusting the amount of water. Antiagglomerants (AAs) and other additives may be necessary to control the hydrate-crystal size and prevent solid blockage in these systems. Where possible, it is proposed to use a closed-loop concept that allows partial recirculation of the liquid phase and its associated additives. The recycled fluid acts as carrier fluid, transferring produced hydrocarbons to their destination (e.g., platform). In this case, part of the additives, including AAs, can be recycled, reducing the operational costs and potential environmental impact. This paper presents the latest developments of the HYDRA- FLOW technology, including studies on hydrate-growth rates, viscosity/transportability of slurries for different low- and high- gas/oil-ratio (GOR) systems, and the effect of salts from reservoir brines and/or seawater.