作者：Mahesh Sonawane 和 Ben Toleman，2H Offshore

海底油井干预类似于汽车的定期保养。虽然保养起来可能很麻烦，但对汽车的使用寿命和性能来说却至关重要。同样，海上油井也会随着时间的推移而枯竭，并遇到阻碍石油生产的问题。为了恢复最佳性能，油井干预是必不可少的。 

干预作业具有经济效益，因为提高油井产量可以增加收入并抵消干预作业的成本。不过，业内仍希望尽量减少维护并降低油井干预成本。无立管油井干预：近年来，无立管轻型油井干预 (RWLI) 在墨西哥湾越来越受欢迎，已成为运营商的一个有吸引力的选择。全球范围内，RLWI 市场预计将在 2020 年至 2027 年期间以 5.2% 的速度增长，达到 25 亿美元。市场受到石油和天然气、海底勘探和生产需求不断增长以及与传统立管方法相比 RLWI 的成本效益的推动。

虽然基于立管的干预是一种可靠的解决方案，但由于需要专用的立管系统、干预套件和能够处理立管的船只，因此通常更耗时且更昂贵。

另一方面，无立管机械或液压干预系统可以通过较小的随机船只进行操作，并可在更短的时间内完成。

基于立管的干预系统的优势在于拥有标准化的立管系统，可从各种 OEM 获得，从而简化并减少系统集成的需求。相比之下，无立管下线干预系统不是标准解决方案；它们需要精心规划、系统集成方法和定制的井专用解决方案。因此，基于立管的干预类似于从大型零售商处购买现成产品，而无立管系统更像是在 Etsy 上购物，定制和独特的解决方案是关键。

本文探讨了机械和液压无立管干预系统的要素，并概述了各种选项。本文将讨论配置和基本优化，以及缓解在海上部署该系统时遇到的运营挑战所需的系统级分析。无立管系统中的典型下行线可以包括：

• 流通下线。
• 从下线到油井的灵活飞线。
• 控制脐带和脐带终止组件。
• 机械干预绳索。
• 海底干预包。
• 循环管线和脐带的被动断开机制。

循环管线

用于泵送流体的循环管线可以是盘管或小直径钻杆。根据操作要求，可能有一条或两条循环管线。对于盘管，管道可以通过注入头或向下滑轮部署。如果使用由带螺纹连接的钻杆制成的循环管线，并且钻机配备有处理和运行钻杆的设备，则循环管线部署到泥浆线上方 100-200 英尺的深度。在此深度，可以使用重块来保持管线的张力并防止由于环境负荷（例如水流和波浪）而导致的过度移动。为了完成循环回路，从盘管或钻杆的底部到井部署了一条柔性软管。这种柔性软管在系统中提供了一定的柔顺性，允许船舶在离井一定距离内移动，而不会对海底采油树或井结构施加机械负荷。

从下线到井的柔性软管

柔性软管可以是粘合或非粘合柔性管，也可以是复合管。根据管道的重量和弯曲刚度，需要评估柔性管在水中部署时将采用的悬链形状。

管道可能形成 J 形或 U 形悬链线，并带有下垂弯头，如图 3 所示。如果与海底采油树的插入角度相对于水平方向向下，则这种配置是可以接受的。如果插入角度是垂直的，则可能需要浮力来帮助管道漂浮并保持垂直插入角度。在某些情况下，海底连接处可能需要旋转接头，以防止柔性管道承受过度弯曲或扭转负载。

控制脐带和脐带终止组件

控制脐带对于为海底干预设备提供液压和电力至关重要。它可以以各种方式部署。如果脐带足够坚固，能够在数千英尺的水深中支撑其自身重量，则可以独立部署。或者，可以使用钢丝绳部署控制脐带，夹具间隔足够的距离以支撑脐带的重量。脐带与脐带端接组件一起部署。

在某些配置中，如果由电缆支撑，脐带终端组件可以自由悬挂，其重量由电缆支撑。另一方面，可以在井附近部署泥垫，并将脐带终端组件降落在其上。这需要脐带中有足够的下垂度或悬链线，以防止其对泥垫施加过大的负载或由于环境负载和船舶运动而将脐带终端组件从泥垫上抬起。 

机械干预电缆和海底干预包

机械干预系统由压力控制头、润滑器、海底干预包、电缆和工具串组成。润滑器可能非常高，高度在 50-90 英尺之间，自由地立在干预包上。部署在润滑器内的电缆和工具串必须具有足够的净空以执行操作并适应环境负载和船舶运动。净空不足会导致电缆拉动润滑器阀门，从而导致海底设备和井的弯曲负载过大。

循环管线和脐带的被动断开机制

钻井立管和干预立管系统配备了主动紧急断开系统 (EDS)，该系统可以在紧急情况下（例如船舶停电和位置丢失）将立管与井断开。另一方面，无立管下线系统主要依靠被动系统，尽管它们偶尔可能包括主动断开系统。被动 EDS 是一种触发机制，旨在在特定额定负载下断开，将下线与井断开，以防止海底采油树或井架承受过大负载。这可以采用剪切销、带槽螺栓或断头台的形式，可以剪断柔性软管或脐带缆以断开连接。

至关重要的是，被动断开机制的设计必须符合规范，当井处于危险状态时，可通过断开干预系统来确保安全操作。然而，这些系统也必须经过校准，以避免意外触发或误报，这可能会扰乱较为温和的日常环境中的正常操作。

系统优化

传统上，不同的下线被视为单独的元素，每个元素都根据其自身的性能进行配置。此外，每个系统的分析都是其各自的 OEM 的责任。然而，这种方法并不总是能产生最好的结果，因为系统需要集成才能为操作员或最终用户提供最有效、最安全的解决方案，从而最大限度地减少停机时间并最大限度地提高安全性。

根据作业规范选定下线选项后，系统集成的第一步是进行系统级分析，以微调船舶的几何形状、配置和部署位置。优化不同下线的配置是关键步骤，可以防止 90% 以上的潜在作业问题。

盘管下线的关键决定是船上的部署位置。对于包括电缆系统的机械干预，船只必须直接位于井中心上方。但是，盘管可以从月池边缘、穿过月池、从船侧或从船尾部署。这取决于船的甲板布局。部署位置确定后，接下来要考虑的是是否需要配重块、配重块的重量、  其距泥线的高度以及柔性软管的相关长度。较重的配重块将最大限度地减少盘管的位移并减少应力。但是，为了便于操作，最好使用尽可能小的配重块。 

优化过程的下一步是确定被动断开机构的尺寸并指定其断开负载额定值。被动 EDS 可在紧急情况下保护下线设备和井下设备。

选择所有下行线配置后，可以建立整个系统的整体模型，并对船舶相对于其标称位置朝向井眼、远离井眼和垂直于井眼的一系列运动进行初步分析。

此外，还应分析一系列环境电流和波浪载荷。该分析确定了所有下行管线的载荷和行为，从而可以开发一个安全操作窗口，所有下行管线都可以在此窗口中安全运行。在此窗口的边界处，被动断开系统应安全地将下行管线与井分离。完成此评估后，将为集成下行管线系统建立一个安全操作区或操作窗口。图 2 显示了操作窗口的示例。

结论

无立管井干预装置中下管的有效性与初始配置和标称设置密切相关。利用全局模型可以更好地了解连续油管特性如何影响柔性跳线配置以及不同下管如何相互作用。船舶位置和下管部署位置的战略性放置对于管理柔性软管的弯曲半径和连续油管上的表面应力起着至关重要的作用

为了提高可操作性并最大限度地减少停机时间，重要的是优化船舶位置以适应各种环境情景，调整重块高度以管理软管松弛，并根据灵活的插入角度有效使用浮力模块。这些措施共同提高了海底作业的效率和可靠性。DC  

By Mahesh Sonawane and Ben Toleman, 2H Offshore

Subsea well intervention is akin to the regular maintenance of a car. While it can feel like an inconvenience to get it serviced, it is essential for the longevity and performance of the car. Similarly, offshore wells deplete over time and encounter issues that hamper oil production. In order to restore peak performance, well intervention is necessary. 

There are economic benefits to an intervention operation, as increased well production boosts revenue and offsets the cost of the intervention operation. Still, there is a desire in the industry to minimize maintenance and reduce the cost of well intervention. Enter riserless well intervention: Gaining traction in the Gulf of Mexico in recent years, riserless light well intervention (RWLI) has become an attractive option for operators. Globally, the RLWI market is expected to grow at a rate of 5.2% from 2020 to 2027, reaching $2.5 billion. The market is being driven by the increasing demand for oil and gas, subsea exploration and production, and RLWI’s cost effectiveness compared with traditional riser-based methods.

While riser-based intervention is a robust solution, it is often more time-consuming and expensive due to the need for a dedicated riser system, intervention package and a vessel capable of handling a riser.

Riserless mechanical or hydraulic intervention systems, on the other hand, can be operated from smaller vessels of opportunity and can be accomplished in a faster time frame.

Riser-based intervention systems offer the advantage of having a standardized riser system, available from various OEMs, which simplifies and reduces the need for system integration. Riserless downline intervention systems, in contrast, do not come as standard solutions; they require meticulous planning, a system integration approach and customized well-specific solutions. So, where a riser-based intervention is analogous to purchasing an off-the-shelf product from a big box retailer, a riserless system is more akin to shopping on Etsy, where customization and unique solutions are key.

This article explores the elements of mechanical and hydraulic riserless intervention systems and provide an overview of the various options. Configuration and essential optimization will be discussed, as well as the system level analyses required to mitigate operational challenges encountered while deploying this system offshore. Typical downlines in a riserless system can include:

• Circulation downlines.
• Flexible flying leads from downline to the well.
• Control umbilical and umbilical termination assembly.
• Mechanical intervention wireline.
• Subsea intervention package.
• Passive disconnect mechanism for the circulation line and umbilical.

Circulation lines

The circulation line for pumping fluids can be either coiled tubing or small-diameter drill pipe. Depending on the requirement of the operation, there may be one or two circulation lines. For coiled tubing, the pipe can be deployed through an injector head or over a turn-down sheeve. If using circulation lines made of drill pipe with threaded connections, and the rig is equipped to handle and run drill pipe, the circulation lines are deployed to a depth of 100-200 ft above the mud line. At this depth, a clump weight can be employed to maintain the line in tension and prevent excessive movement due to environmental loads, such as currents and waves. To complete the circulation loop, a flexible hose is deployed from the base of the coiled tubing or drill pipe to the well. This flexible hose provides some compliance in the system, allowing the vessel to move within a certain distance from the well without imposing mechanical loads on the subsea tree or well architecture.

Flexible hose from downline to the well

The flexible hose can be a bonded or unbonded flexible pipe, or a composite pipe. Depending on pipe’s weight and bending stiffness, it is necessary to evaluate the catenary shape the flexible pipe will adopt when deployed in water.

The pipe may form a J-shaped or U-shaped catenary with a sag bend as shown in Figure 3. This configuration is acceptable if the stab-in angle with the subsea tree is orientated downward relative to the horizontal. If the stab-in angle is vertical, buoyancy may be required to help the pipe float and maintain a vertical stab-in angle. In some cases, a swivel may be required at the subsea connection to prevent excessive bending or torsional loads on the flexible pipe.

Control umbilical & umbilical termination assembly

A control umbilical is essential for providing hydraulic and electrical power to the subsea intervention equipment. It can be deployed in various ways. If the umbilical is sufficiently robust to support its own weight over thousands of feet of water depth, it can be deployed independently. Alternatively, the control umbilical can be deployed using a wireline, with clamps spaced at sufficient interval to support the umbilical’s weight. The umbilical is deployed along with the umbilical termination assembly.

In certain configurations, if supported by a wireline, the umbilical termination assembly can hang freely with its weight supported by the wireline. On the other hand, a mud mat may be deployed in the vicinity of the well and the umbilical termination assembly landed onto it. This requires sufficient sag or catenary in the umbilical to prevent it from exerting excessive loads on the mud mat or lifting the umbilical termination assembly off the mud mat due to environmental loads and vessel motions. 

Mechanical intervention wireline & subsea intervention package

The mechanical intervention system consists of the pressure control head, lubricators, subsea intervention package, wireline and tool string. The lubricator can be quite tall, ranging from 50-90 ft in height, standing freely on the intervention package. The wireline and tool string deployed within the lubricator must have adequate headroom to perform the operations and accommodate for environmental loads and vessel motions. Insufficient headroom can cause the wireline to pull on the lubricator valve, leading to excessive bending loads on the subsea equipment and the well.

Passive disconnect mechanism for circulation line & umbilical

Drilling risers and intervention riser systems are equipped with an active emergency disconnect system (EDS) that can disconnect the riser from the well in emergencies, such as vessel blackout and loss of position. The riserless downline systems, on the other hand, primarily rely on passive systems, though they may occasionally include an active disconnect system. A passive EDS is a trigger mechanism designed to break at a specific rated load, disconnecting the downline from the well to prevent excessive loading on the subsea tree or well architecture. This can take the form of a shear pin, a notched bolt or a guillotine that can shear the flexible hose or umbilical for disconnection.

It is crucial that the passive disconnect mechanisms are designed to a specification that ensure safe operations by disconnecting the intervention system when the well is at risk. However, these systems must also be calibrated to avoid accidental triggers or false alarms, which could disrupt regular operations in more benign day-to-day environments.

System optimization

Traditionally, different downlines were considered as individual elements, each configured based on its own performance. In addition, each system’s analysis was the responsibility of its respective OEM. However, this approach does not always produce the best outcome, as the system needs to be integrated to provide the most efficient and safe solution for the operator or end user, minimizing downtime and maximizing safety.

Once the downline options have been selected, based on the specifications of the operations, the first step in system integration is conducting a system-level analysis to fine-tune the geometries, configurations and deployment locations from the vessel. Optimizing the configuration of different downlines is a key step and can prevent over 90% of potential operational issues.

A key decision for the coil-tubing downline is the deployment location on the vessel. For a mechanical intervention that includes a wireline system, the vessel must be positioned directly above the well center. However, the coil tubing can be deployed from the edge of the moonpool, through the moonpool, from the side of the vessel, or from the aft of the vessel. This depends on the vessel’s deck layout. Once the deployment location is finalized, the next considerations are whether a clump weight is required, how much it should  weigh, its elevation from the mudline, and the associated length of the flexible hose. A heavy clump weight will minimize displacement of the coil-tubing pipe and reduce the stresses. However, there is a preference for the smallest possible clump weight to ease handling. 

The next step in the optimization process is to size and specify the breakaway load rating of the passive disconnect mechanism. The passive EDS protects the downline equipment and the well equipment in case of emergencies.

After all downline configurations have been selected, a global model of the entire system can be built and preliminary analysis conducted for a range of vessel movements relative to its nominal position going toward the well, away from, and perpendicular to the well.

In addition, a range of environmental currents and wave loading should be analyzed. This analysis determines the loads and behavior of all downlines, allowing for development of a safe operating window within which all downlines can operate safely. At the boundaries of this window, the passive disconnect system should safely disengage the downlines from the well. Upon completion of this assessment, a safe operating zone or operating window will be established for the integrated downline system. An example of an operating window is shown in Figure 2.

Conclusion

The effectiveness of downlines in a riserless well intervention setup is intricately linked to the initial configuration and nominal settings. Utilizing a global model allows for better understanding of how coiled tubing characteristics affect flexible jumper configurations and how different downlines interact. The strategic placement of vessel positions and downline deployment locations plays a crucial role in managing the bend radius of flexible hoses and the surface stress on coiled tubing

To enhance operability and minimize downtime, it’s important to optimize vessel positions for various environmental scenarios, adjust clump weight elevation to manage hose slack, and use buoyancy modules effectively based on flexible stab-in angles. These measures collectively improve the efficiency and reliability of subsea operations.  DC