Laws and control of multiple-point leak in the completion string of high-sulfur gas well

In harsh downhole environments, the tubing-casing annulus of high-sulfur gas well frequently suffer multiple-point leak, which leads to the increase of annulus pressure and the drop of annulus liquid level, so as to threaten its wellbore integrity and safe production seriously. Three multiple-point leak models were summarized based on the possible combinations of leak point in completion strings, i.e., upper leak point+thread leak at the lower leak point, upper leak point+body leak at the lower leak point, and upper leak point+packer leak. And the increasing laws of annulus pressure and the dropping laws of annulus liquid level corresponding to each leak model were analyzed. It is indicated that when it is thread leak with gas running through instead of liquid at the lower leak point, it only speeds up the multiple-point leak. When it is body leak with gas and liquid running through at the lower leak point, the state of " coexistence of gas leak in the upper part of the annulus and liquid leak in the lower part” occurs in the process of leak. And when it is packer leak at the lower leak point, the mode of obvious increasing and sharp decline occurs many times in the increasing process of annulus pressure, and the annulus liquid level drops in the shape of step. Finally, based on the actual situations of high-sulfur gas wells and the laws of multiple-point leak, three control measures with the advantages of simple operation, convenient field implementation and low cost were put forward, including downhole throttling technology, calcium carbonate plugging technology, and high-viscosity, low-density annulus protection liquid technology. They present good field application results and can be popularized and applied in similar high-sulfur gas fields.