Study and Application of Phase Curve of Hydrates in Deep Water Gas Well Testing

In deep water gas well testing, changes in the temperature field of the wellbore usually result in a huge risk-the formation of hydrates. The hydrate generated will cause test pipes to block, and the annular space to have high pressure. Study has been conducted on the application of the phase curve of hydrate generation in deep water gas well testing. Based on an accurate prediction of the wellbore temperature field in deep water gas well, the area inside the test string in which hydrate will be generated during well testing is quantitatively predicted using the phase curve of hydrate, the depth at which the chemical injection valve is run on the test string is calculated, and the amount of hydrate inhibitor injected in wellbore and at the surface (choke) during testing is determined. All these together form the method of using the phase curve of hydrate in deep water well testing. This method has been used on a deep water gas well in South China Sea. The depth at which the chemical injection valve was run was calculated to be 2,450 m. Two hydrate inhibitors, methanol and glycol (3%-5%), were injected into the wellbore and at the choke on the surface respectively. Well testing was done in accordance with the standard work system, no hydrate had ever occurred in the wellbore during testing. Hydrate was produced at the choke, and after injecting hydrate inhibitor, the pressure was reduced by 13.6%, ensuring the success of the well testing operations. The operation procedure can be used for reference in controlling the formation of gas hydrate during well testing in deep water gas fields.