Abstract Sustained casing pressure (SCP) caused by tubing leakage is mostly considered as the dangerous situation in gas wells, which is more likely to pose a serious threat to well integrity and environmental protection. In order to assess the downhole risk in early time and further provide maintenance strategies to optimize well performance, it is necessary to diagnose the source of downhole leakage accurately. This paper presents a pressure-balance-based approach for capturing two types of dynamic annulus pressure behaviors in a gas well with SCP caused by tubing leakage at different well depths. The approach includes models that take into account the influence of temperature and pressure distributions of tubing and annulus fluid, which are used to determine tubing leakage points. In addition, such an approach involves the calculation of maximum annulus pressure at the wellhead in a gas well with SCP under four main cases, representing the effects of the leakage location, bottom hole pressure, annulus liquid level and gas production rate on wellhead pressure. Afterwards, an integrated diagnostic testing system has been developed to monitor the synthetic state of annulus fluid and liquid level parameters, ultimately identifying the source of SCP correctly. In contrast to previous works, leakage diagnostic testing can be performed from an offshore platform, and it meets the requirements of offshore field testing and works without a shut-in condition, which is capable of overcoming limitations of downhole detection. A case study focused on an offshore gas well with SCP is presented to illustrate the feasibility of the proposed approach, and also to demonstrate that leakage diagnosis contributes to the mechanism investigation of SCP, as well as the design improvement of gas wells integrity.

中文翻译：

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海上平台持续套管压力气井泄漏诊断测试模型

摘要 油管泄漏引起的持续套管压力（SCP）大多被认为是气井的危险情况，更可能对井的完整性和环境保护构成严重威胁。为了早期评估井下风险并进一步提供维护策略以优化井性能，有必要准确诊断井下泄漏源。本文提出了一种基于压力平衡的方法，用于捕获具有 SCP 的气井中由不同井深油管泄漏引起的两种动态环空压力行为。该方法包括考虑油管和环空流体的温度和压力分布影响的模型，用于确定油管泄漏点。此外，这种方法涉及在四种主要情况下计算具有SCP的气井井口最大环空压力，代表泄漏位置、井底压力、环空液位和产气率对井口压力的影响。随后，开发了一套综合诊断测试系统来监测环空流体的合成状态和液位参数，最终正确识别SCP的来源。与以往的工作相比，泄漏诊断测试可以在海上平台上进行，满足海上现场测试的要求，无需关井即可工作，能够克服井下检测的局限性。介绍了一个专注于具有 SCP 的海上气井的案例研究，以说明所提议方法的可行性，