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阿拉伯湾的许多运营商运营着价值数十亿美元的资产。大量油井的生产井寿命尽可能长，最小设计寿命为25至30年。

现场观察表明，实际寿命在 7 至 25 年之间，主要是由于油井完整性下降。这是运营商非常关心的问题。除了生产作业的安全和环境方面的重要性之外，如果没有足够的井完整性，井就不可能达到油田开发计划中预期的全部产量潜力。

石油和天然气行业采用两种不同的方法来确保油井完整性。第一种是基于监测和补救行动的反应方法。例如，2015 年 10 月加州发生天然气泄漏，花了几个月的时间才得到控制（见照片）。第二种方法是积极主动的方法，例如安装阴极保护（CP）系统，以尽可能防止腐蚀的发生。

泄漏井正在连接一个泄压井，希望在工程师尝试密封泄漏的同时，所有气体都能转移到那里。（迪恩·穆斯格罗夫 / 洛杉矶每日新闻，美联社，普尔）

含水层的外部腐蚀：中东的潜在威胁

如今中东生产的许多油井都是几十年前完工的，腐蚀控制和监测并不是主要问题。在最初的开发阶段，没有足够的知识和专业知识来预测未来任何油田范围内的井完整性问题。

此外，中东地区腐蚀机制的性质使其基本上保持“沉默”，对大量油井构成“沉睡”的威胁。当时，常规生产了解、监测和地球化学分析无法检测到所观察到的电化学腐蚀。

因此，当浅水含水层突然开始发生大量腐蚀故障时，尤其是在装有多个同心套管的井上，井完整性问题的管理变得复杂。

多个屏障上的电化学活性和外部腐蚀过程最初集中在最外层套管上，导致壁厚大幅减薄，在极端情况下，甚至损坏了外层套管。在其非常严重的阶段，这种全面腐蚀已经突破到最里面的套管，因此形成了孔洞。

当发生套管泄漏时，含水层水可能通过管道或封隔器泄漏直接与生产层相连，从而增加了地下井喷和浅水含水层碳氢化合物储量损失的风险。这还因饮用水污染而带来另一个 HSE 风险。

影响中东油井完整性的主要因素

现场调查显示，造成中东地区油井完整性问题的三个主要因素：

1. 漏失区
2. 浅层含水层的测压
3. 含水层的水动力活动

循环漏失区 (LCZ)：钻井过程中遇到的循环漏失区对井的完整性产生巨大影响。从地表到 7500 至 8000 英尺的每个区域通常都会出现部分或全部损失。无效的原生水泥并不罕见，这可能导致最外层屏障暴露于电化学活性。

当在浅层含水层中获取裸眼测井时，它们显示孔隙度通常高达 40% 甚至 50%，渗透率约为几个达西。由此产生的生产力或注入指数非常高，因此含水层具有无限的作用。

水位下降仅为 5 psi，含水层每天可以向地表产生超过 5,000 B/D 的水。如果最外套管没有安装阴极保护系统，这些LCZ将充当“节点”。LCZ在同一地层​​内具有非常尖锐的电阻率对比，因此它充当阳极。另一种情况是，当安装了阴极保护系统时，这些LCZ将充当保护电流的汇点，因此，在这些LCZ以下无法实现可靠的保护。

浅层含水层测压：从中东地区主要油田的代表性井获取的压力采样数据表明，一些饮用水储层的测压水平高于地表，有效地形成了高孔隙压力的含水层。这意味着，如果这些井的完整性由于含水层处的水泥损坏和/或套管腐蚀而受到损害，水可能会直接流到地表。在这种情况下，这可能会导致地表流出、地下井喷或横流。

水动力活动：浅层含水层中氧气的持续补充是由从较高的地面/山丘流出的雨水进行的典型补给造成的。人们发现这个充满氧气的滨水区正在移动，示踪剂调查显示，海湾地区的一个田地的移动速度为 12 m/年。这种流体动力流动会导致腐蚀。

防止外部腐蚀的缓解原则

石油和天然气运营商主动使用称为阴极保护 (CP) 系统的电化学技术来控制地下井结构和海洋结构的外部腐蚀。CP 还用于控制含水的储存、生产和加工容器的内部腐蚀。在许多情况下，涂层与 CP 系统配合使用，有助于提供更可靠的保护并降低 CP 电流要求。

通过使用耐腐蚀金属、惰性保护涂层（涂层管、水泥保护套）或在流体中引入化学抑制剂，可以减少（在某些情况下消除）腐蚀的影响。

不幸的是，从历史上看，井下腐蚀测量和数据并没有被用来设计现场阴极保护系统，这通常导致许多阴极保护系统的成功率较低。如果结合腐蚀测井并了解其作用机制，就可以设计出成功的阴极保护系统。

获取有关屏障特性的反馈

在井寿命的多个阶段进行适当的电缆腐蚀测井是获得准确的阻隔性能的关键输入，该阻隔性能可能随时间动态变化。采用详细且一致的测井评估来了解问题的位置、严重程度、原因及其对修井的影响。

由于腐蚀可能是由多种原因造成的，因此最好结合使用多种监测技术，以获得对问题的全面、协同解释和准确理解。此外，电缆评估对于优化阴极保护系统设计和建立所需的设计参数至关重要。

市场上有多种使用电磁、超声波、机械或电气原理的有线测量技术。这些技术可以提供丰富的油井完整性数据，如下所示：

时域电磁设备：来自脉冲涡流测量的时域信号具有径向敏感的衰减特性。它能够检测、定位和测量四个套管中的孔洞、裂缝、内部和外部腐蚀以及金属损失。

• 超声波设备 USL： USL 使用脉冲声波在套管壁内反射和共振，给出内半径、套管厚度和最内层屏障的水泥特性。
• 机械成像设备：机械手指用于测量内径变化并评估油管或套管的几何形状。
• 腐蚀速率设备：腐蚀速率工具通过测量电势差来检测沿套管的电流和流入地层的径向电流。

案例历史：Arab-C 地层套管失败

该现场案例讨论了尽管有令人印象深刻的电流保护系统，但由于现场外部腐蚀而导致的套管故障。过去，Arab-A 至 C 地层没有问题，但相对较新的井出现了大量套管泄漏。如下图所示，Arab D 是生产油藏，位于Arab-A 至C 地层正下方，预计许多井将通过井眼或管道后连通。

在 6,500 英尺至 6,200 英尺的井龄不到 10 年的井中发现外部腐蚀

成立了一个多学科的井完整性团队，以探索阿拉伯-C 到 D 的通信问题，并审查在现有和未来井中保持套管完整性的选项。该团队致力于识别和评估阿拉伯套管泄漏的主要影响因素，并提出预防措施建议，以避免在该领域和其他领域再次发生类似情况。

根据井下测量，得出的结论是，严重的外部腐蚀是阿拉伯-C 与其他地层流体（Sulaiy/Yamama 地层）之间自我持续的长线电化学相互作用的结果，该流体与套管接触并建立了“长线”腐蚀池。腐蚀是由于阴极保护系统竣工和调试之间暴露时间过长以及整个阿拉伯-C 水库阴极保护本身不足共同造成的。

此外，得出的结论是，需要极高水平的 CP，在完井后立即需要 45 安培的 CP 电流快速极化。

该案例显示了主要通过使用集成日志应用程序来确定腐蚀机制的调查工作。

这项工作中使用的电缆井完整性测井是：

• 电势分布测井可确定各种条件下生产时的轴向电流分布。
• 用于生产套管后面的腐蚀和水泥评估的超声波测井。
• 用于评估单个和多个障碍的电磁测井。

该油井的阴极保护系统在钻井前安装完毕，准备在完井后立即投入使用。在应用CP系统之前，该井在没有油管的情况下应用了综合测井，并在6个月后再次运行该计划。
下图显示了整流器输出关闭时的诊断日志应用程序。右侧所示的水泥图显示，由于水泥凝固过程中盐水与水泥环的相互作用，阿拉伯-C 地层中的水泥环受到污染。上面和下面的区域是硬石膏形成，这是水泥质量优良的原因。电位剖面调查显示大量阳极电流从套管释放到地层中。所有三个独特的阳极区均位于阿拉伯-A 至-C。

下图显示了在以下三种条件下测得的复合轴向套管电流测井：

• 下套管井筒后，未施加CP（红线）
• 部分极化 4 小时后，应用 CP（蓝线）
• 6个月高后，应用CP（绿线）

各种条件下综合测井的主要目的是确定在完井后是否可以通过对高 CP 系统通电来减轻阿拉伯-A 至 -C 地层中发生的腐蚀机制。最初，高 CP 似乎会有效。

油田整体井完整性管理的结论与建议

根据在不同项目中获得的经验，建议研究历史和当前的井完整性数据，以减轻井完整性问题。研究结果得出的结论是，采用延时腐蚀检查测井策略，旨在调查关键代表性井随时间的腐蚀进展，将延长生产井的预期寿命，从而有助于延长生产井的寿命。现场生产力。

除了深入研究井完整性数据库之外，集成裸眼井、地球化学分析、钻井和其他相关数据集将有助于深入了解影响井寿命的根本原因。

以下几点总结了油田关键井的延时测井所增加的价值。

• 确定井之间的腐蚀关系。
• 绘制现场高风险区域地图。
• 识别需要补救的病井，并确定准确的修井计划和 CP 优化，这可能意味着通过减少感应电流来降低 CP 成本。
• 确定整个油田井完整性问题的根本原因，并采用具有成本效益的解决方案。
• 允许生产团队及时计划可能需要的任何预防性维护，以防止油井完整性恶化以及可能造成非常重要资产（例如生产井）或 HSE 事件的损失。

参考

NACE-08016：Arab-C 地层套管失效调查，作者：Darrell R. Catte

NACE 论文：Arab-C 油藏外井套管腐蚀 作者：Ahmad Al Sahhaf 和 Darrell Catte

SPE 93184 井下腐蚀测井综合分析以调查套管泄漏，作者：YY Al-Ghasham、DR Catte 和 AA Al-Haji，沙特阿美公司： https: //doi.org/10.2118/93184-MS

SPE 172736 解决配备 ESP 的生产现场中神秘的套管故障问题，作者：Simina Al Mahrooqi、Muhammad Khalid Azim： https: //doi.org/10.2118/172736-MS

Muhammad Khalid Azim TAQA 良好完整性领域冠军

Raid Bukhamseen TAQA SAOO 客户高级经理

Why Well Integrity?

Many operators in the Arabian Gulf operate assets that are worth several billions of dollars. The bulk stocks of wells are intended to have a production well life as long as possible with a minimum design age of 25 to 30 years.

Field observations indicated the actual life span to be between 7 and 25 years, mainly due to degraded well integrity. This is of great concern for operators. Besides the importance of safety and environmental aspects of the production operations, without adequate well integrity, wells are unlikely to reach their full production volume potential as intended in the field development plan.

There are two distinct approaches to well integrity assurance adopted in the oil and gas industry. The first is a reactive approach based on monitoring and remedial action. For example, a California gas leak back in October 2015 which took several months to control (see photo). The second approach is a proactive approach like installing a cathodic protection (CP) system to prevent corrosion from occurring as much as possible.

A relief well is being connected to the leaking well in the hopes that all the gas can be diverted there while engineers try to seal the leak. (Dean Musgrove/Los Angeles Daily News via AP, Pool)

External Corrosion Across Aquifers: A Sleeping Threat in the Middle East

Many of the wells producing today in the Middle East were completed several decades ago, where corrosion control and monitoring were not a primary concern. At the initial development stage, there was not enough knowledge and expertise available to anticipate any future fieldwide well integrity problems.

Moreover, the nature of the corrosion mechanism in the Middle East was such that it essentially remained "silent," a "sleeping" threat to a large number of wells. At that time, the observed electrochemical corrosion was not detectable with routine production understanding, surveillance, and geochemical analysis.

As a result, the management of well integrity issues became complicated when numerous corrosion failures suddenly started to occur across shallow-water aquifer levels, especially at levels where wells were cased with multiple concentric casings.

The electrochemical activity, and external corrosion process on multiple barriers, initially concentrated at the outermost casing, which resulted in extensive wall thinning, and in extreme cases, destroyed the outer casing. At its very advanced stage, this general corrosion had broken through to the innermost casing(s), and consequently, holes were developed.

When a casing leak develops, the aquifer water can come in direct communication with production pay through tubing or packer leak, increasing the risk for subsurface blowout and loss of hydrocarbon reserves to shallow-water aquifers. This also imposes another HSE risk by contamination of potable water.

Major Factors Influencing Well Integrity in the Middle East

Field investigations showed there are three primary factors contributing to well integrity issues in the Middle East region:

1. Lost circulation zones
2. Piezometric pressure of the shallow aquifers
3. Hydrodynamic activity of water-bearing zones

Lost Circulation Zones (LCZ): Zones with lost circulation encountered during drilling have a drastic effect on well integrity. Partial or total losses are usually seen in every field starting from surface down to 7500 to 8000 ft. Ineffective primary cement is not unusual, which can result in the outermost barrier being exposed to electrochemical activity.

When openhole logs were acquired across shallow aquifers, they indicated usually porosity in the range up to 40% or even 50%, and permeability in the order of a few Darcys. The resulting productivity or injectivity indices are very high and aquifers are therefore infinite acting.

With a drawdown of just 5 psi, the aquifer can produce more than 5,000 B/D of water to the surface. If no cathodic protection system for the outermost casing is installed, these LCZ will act as “anode.” The LCZ has a very sharp resistivity contrast within the same formation, therefore it acts as an anode. In another case, when there is a cathodic protection system installed, these LCZ will act as a sink for the protection current, and as a result, no solid protection can be achieved below these LCZ.

Piezometric Pressure of Shallow Aquifers: The pressure sampling data acquired from representative wells across the main fields in the Middle East region showed that some potable water reservoirs had piezometric levels above the surface, effectively creating aquifers with high pore pressure. This means that if the well integrity of these wells is compromised due to cement impairment and/or casing corrosion at the aquifer level, water can flow directly to the surface. This can result in a surface flowout, subsurface blowouts, or cross flows in such cases.

Hydrodynamic Activity: The continuous replenishment of oxygen in shallow aquifers results from the typical recharging which occurs from rainwater that runs off from higher ground/hills. This oxygen-charged waterfront is found to be moving, as tracer surveys indicated a speed of 12 m/year in a field in the Gulf region. This hydrodynamic flow can lead to corrosion.

Mitigating Principles To Arrest External Corrosion

Oil and gas operators proactively use an electrochemical technique called a cathodic protection (CP) system to control external corrosion of underground well structures as well as marine structures. CP is also used to control internal corrosion of storage, production, and process vessels that contain water. In many cases, coatings work together with CP systems to help provide more reliable protection and to lower the CP current requirement.

The effects of corrosion can be reduced (and in some cases eliminated) by using resistant metals, inert protective coatings (coated tubing, protective cement sheath), or by introducing chemical inhibitors into the fluid.

Historically, downhole corrosion measurements and data were unfortunately not utilized to design the field CP system, which usually resulted in a low success rate of many CP systems. If combined with corrosion logging and an understanding of the mechanism at play, a successful CP system can be designed.

Getting Feedback on Barriers Properties

Proper wireline corrosion logging at multiple stages over the well life is a critical input in obtaining accurate barrier properties, which may dynamically vary over time. Detailed and consistent log evaluation is applied to obtain understanding on the location, magnitude, cause of the problem, and its impact on well repairs.

Because corrosion can be the result of a wide range of causes, a combination of several monitoring techniques is best deployed to get a comprehensive, synergetic interpretation and accurate understanding of the problem. Additionally, wireline evaluation is essential to optimize the CP system design and to establish the desired design parameters.

Several wireline measurement techniques are available in the market which use electromagnetic, ultrasonic, mechanical, or electrical principles. These technologies can provide a wealth of well integrity data as follows:

Time Domain Electromagnetic Devices: The time domain signal from a pulsed eddy- current measurement has a decay character which is radially sensitive. It has the ability to detect, locate, and measure holes, splits, internal and exterior corrosions, and metal losses in four casings.

• Ultrasonic Devices USL: USL uses pulse sound waves that reflect off and resonate within the casing wall, giving internal radius, casing thickness, and cement properties of the innermost barrier.
• Mechanical Imaging Devices: The mechanical fingers are used to measure the internal-diameter variations and evaluate the geometry of tubing or casing.
• Corrosion Rate Devices: Corrosion rate tools detect current flow along the casing and radial current flow into a formation by measuring potential differences.

Case History: Well Casing Failures in Arab-C Formation

This field case discusses casing failures due to external corrosion in a field despite the impressive current protection system. The Arab- A to C formation were non-problematic in the past but relatively new wells saw the onset of numerous casings leaks. As shown in the figure below, Arab D is the producing reservoir and is located immediately below the Arab- A to C formations and many wells were expected to have through wellbore or behind pipe communication.

External Corrosion Identified Between 6,500 ft to 6,200 ft in Wells Less Than 10-Years Old

A multidisciplinary well integrity team was formed to explore the Arab-C to -D communication problem and review options for maintaining casing integrity in existing and future wells. The team worked to identify and assess the main contributing factors of Arab casing leaks and to recommend preventive measures to avoid a similar reoccurrence in this field and others.

Based on the downhole measurements, it was concluded that severe external corrosion is the result of self-sustained, long-line electrochemical interaction between the Arab-C and other formation fluid, the Sulaiy/Yamama formation, which contacts the casing and establishes a "long-line" corrosion cell. The corrosion results from a combination of an excessively long-time exposure between completion and commissioning of the CP protection system and insufficient cathodic protection itself across the Arab-C reservoir.

Moreover, it was concluded that exceptionally high levels of CP are necessary with a rapid polarization of CP current of 45 amps being required immediately after completing the well.

This case history showed the investigative work carried out to identify corrosion mechanisms primarily by using integrated logs application.

The wireline well integrity logs used in this work were:

• Potential profile logs to determine the axial current profile on production under various conditions.
• Ultrasonics logs for corrosion and cement evaluation behind the production casing.
• Electromagnetic logs for evaluation of single and multiple barriers.

The CP system for the oil well was installed before the well was drilled, ready to be commissioned immediately after well completion. Integrated logs were applied in this well without tubing before applying the CP system, and the plan was run again after 6 months.
The figure below shows the diagnostic log application with rectifier output set off. The cement map shown on the right side showed contaminated cement sheath across Arab- C formation due to brine interaction with the cement sheath during setting up of cement. The zones above and below were anhydrite formation, which is the reason behind excellent cement quality. The potential profile survey showed massive anodic currents were discharging from the casing into the formation. All three distinctive anodic zones were located at Arab-A to -C.

The following figure displays the composite axial casing currents log measured under the following three conditions:

• After landing the casing wellbore, no CP was applied (red line)
• After 4 hours of partial polarization, CP was applied (blue line)
• After 6 months of high, CP was applied (green line)

The main objective of integrated logs at various conditions is to determine if the corrosion mechanism occurring in the Arab-A to -C formation could be mitigated by energizing the high CP system after well completion. Initially, it appeared that high CP would be effective.

Conclusion and Recommendations on the Overall Field Well Integrity Management

Based on experience gained in different projects, it is recommended to study historical and current well integrity data to mitigate well integrity issues. As a result of the study, it is concluded that adopting a strategy of time-lapse corrosion-inspection logging, aiming to investigate the corrosion progress over time in key representative wells, will elongate the production well life expectancy and hence, will aid in prolonging field productivity.

Integrating openhole, geochemical analysis, drilling, and other related datasets, in addition to a deep dive into the well integrity database, will provide insight into the root cause(s) affecting the life of the wells.

The following points summarize the value added by time-lapse logging on key wells across a field.

• Identify the corrosion relations between the wells.
• Map high-risk areas in the field.
• Identify sick wells that require remedy and determine accurate workover planning and CP optimizing, which might mean reducing CP cost by reducing the induced current.
• Identify root cause(s) of the well integrity problems across the field and adopt cost-effective solutions.
• Allow the production team to plan in a timely manner for any preventive maintenance that might be required to prevent the deterioration of well integrity and possible loss of very important assets, such as a production well, or HSE incidents.

References

NACE-08016: Well Casing Failure Investigation in the Arab-C Formation by Darrell R. Catte

NACE Paper: External Well Casing Corrosion across the Arab-C Reservoir by Ahmad Al Sahhaf and Darrell Catte

SPE 93184 Integrated Analysis of Downhole Corrosion Logs To Investigate Casing Leaks by Y.Y. Al-Ghasham, D.R. Catte, and A.A. Al-Haji, Saudi Aramco : https://doi.org/10.2118/93184-MS

SPE 172736 Solving a Mysterious Casings Failure Problem in ESP-Fitted Production Field by Simina Al Mahrooqi, Muhammad Khalid Azim : https://doi.org/10.2118/172736-MS

Muhammad Khalid Azim Well Integrity Domain Champion at TAQA

Raid Bukhamseen Senior Manager SAOO Account at TAQA