高含硫气井完井管柱多漏点泄漏规律与控制

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

恶劣的井下环境使高含硫气井油套环空往往存在多漏点泄漏,不仅会使环空压力上升,同时还会引起环空液面下降,严重威胁该类气井的井筒完整性和安全生产。基于完井管柱泄漏点组合的可能性,总结了上漏点+下漏点丝扣泄漏、上漏点+下漏点本体泄漏和上漏点+封隔器泄漏3种多漏点泄漏模式,并对每种泄漏模式对应的环空压力上升规律和环空液面下降规律进行了分析。研究结果表明:当下漏点为过气不过液的丝扣泄漏时,其对于多漏点泄漏只起一个加速泄漏的作用;当下漏点为过气也过液的本体泄漏时,泄漏过程中会出现“环空上泄气下漏液同存”状态;当下漏点为封隔器泄漏时,环空压力上升过程中会多次出现明显的上升→突降模式,环空液面也会呈现阶梯式下降。结合高含硫气井的实际情况以及多漏点泄漏规律,提出3种操作简单、现场易实施、成本较低的控制措施,包括井下节流技术、碳酸钙堵漏技术和高黏低密度环空保护液技术,现场应用效果良好,可在类似高含硫气田推广应用。

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 highsulfur 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.