作者：Olof Nilsson 和 Aksel Skungland，FourPhase

在当今的能源格局中，运营商不断寻求提高效率、最大限度减少环境影响并最大限度提高油井产能的解决方案。其中一项突破是使用欠平衡连续油管钻井 (UBCTD) 与闭环固体处理系统相结合进行侧钻作业。随着侧钻越来越成为进入新储层的首选方法，了解 CTD 中闭环系统的优势可能是适度成功和最佳井性能之间的区别。 

CT 一直是许多通常在陆上和海上进行的井内干预作业的首选解决方案。它是一种多功能工具，可在不需要全尺寸钻机的情况下使用，用于清理、侧钻、铣削、增产作业、完井、测井和诊断、射孔以及堵塞和废弃等操作。普安）。考虑 CT 的常见原因包括：

• 在地面压力下工作的潜力：它消除了对井进行“填井”的需要，从而可以在带电或欠平衡条件下进行作业。
• 最大限度地减少地层损害：避免引入可能损害地层的压井液，从而保持最佳的储层特性。
• 增强的 HSE：与全尺寸钻机相比，这是通过减少现场人员、减少重型起重需求和简化物流来实现的。
• 节省成本：随着劳动力和设备需求的减少，CT 作业比使用传统钻机更具成本效益，特别是对于修井或小型钻井项目。

传统钻井使用比储层压力更高的静水压力（超平衡）。反之，如果储层压力高于静水压力，则称为欠平衡。与传统钻井相比，欠平衡连续油管铣削和钻井作业既带来了好处，也带来了挑战。

UBCTD的利用为运营商提供了从已建立的储量中获取大量附加价值的机会，并在一次行程中瞄准多个储层区域，从而使枯竭油田的回报最大化。这不仅仅是一个功能，而且是由现场案例支持的运营优势。研究和案例研究表明，UBCTD 在侧钻钻井中非常高效。与传统的超平衡方法相比，它可以减少地层损害，使其成为提高油井产能的有效方法。

此外，UBCTD 可以保持储层的自然渗透率。比较研究表明，在欠平衡条件下碳氢化合物采收率有所提高，这一点得到了支持。

此外，使用双容器旋风除砂器进行 CT 操作可以实现无排放物到达大气的操作。这是通过使用两个旋风容器创建闭环系统来实现的。一个旋风容器可以连续生产，而另一容器中的任何压力在固体排空之前被排出。这确保了固体的连续分离和从井中的流出，并符合环境法规。 

事实证明，应用闭环系统是成功的，并且有利于运营商提高 CT 操作的多功能性，因为在操作过程中可以使用经过处理的海水、化学品、氮气和基础油或类似物。物质保留在系统内，从而减少人员和环境接触潜在危险物质的机会。

闭环系统可用于传统和 CT 设置。DualFlow 除砂器系统连接至 CT 立管组上的流量三通。通常，表面安全阀 (SSV) 安装在除砂器的上游，以实现快速关闭。通过将除砂器连接到带有液位测量的切割箕斗，系统可以始终完全封闭。这确保了没有有害物质释放到大气中。在传统操作中，返回物产生至摇床，操作员存在暴露于 H2S、苯和 NORM（天然放射性物质）的风险。

设计带有旋风除砂器的闭环系统的能力在于其自动化。该系统对分离的固体进行实时测量。通过持续监测分离固体的重量/体积，决策可以基于操作事实而不是估计。其他好处包括：

固体数据的解释以及估计的固体计算可以提供有价值的数据，以提高 CT 操作的效率和质量。

实时决策：随着 CT 操作的运行，固体被标记，清理开始。如果已知固体的预期重量，则当去除的固体体积与预期结果不符时，可以立即更改操作计划。然后可以采取措施，例如增加泵送速率或进一步从孔中抽出。

防止与 CT 卡住相关的问题：CT 卡在井中可能会导致多种情况，包括操作时间损失、工具被释放到需要将其捞出的井中的风险，或者在最坏的情况下，一口关闭的井。

以最佳速度运行的信心：操作员希望尽可能快地运行 CT。如果数据显示固体正在出现，操作员将有信心以最佳速度继续进行。使用与估计数据相关的实时数据可以确保并优化 CT 清理的质量。通过观察实时数据，可以随时随地做出决策。一旦数据和趋势显示井筒干净，线圈就可以有效地移动到下一步/咬合。这可以通过以下知识来完成：盘管工具串后面的所有固体都已从井中一路清除。

确保正确的清理：通过实时分析数据，可以验证固体是否按计划且一致的方式被清理。这意味着上部的闭环砂管理系统可以以最佳且高效的方式处理固体，从而转化为经济效率并减少非生产时间（NPT）。紧凑的固体塞会影响分离效率。如果发生这种情况，所有堆积的沙子将被移出，形成一个紧凑的巨大沙塞。这会给砂管理系统带来压力，其效率可能会降低。这可能导致沙子到达加工设施。

北海案例研究

为了确保挪威大陆架油田的更高产量，开展了一项 CT 活动，在三年内清理增产井。该活动包括八口井和几个增产区。CT 清理
计划使用氮气和基础油的混合物来产生更轻的液柱，从而减少对油藏的压力。为了避免接触包括氮气混合物在内的有害物质，需要一个闭环系统。由于 CT 在船上分布，可用的甲板空间有限，因此需要一种紧凑的解决方案来分隔回水。此外，客户希望系统能够确保刺激后无固体流动。

FourPhase 固体管理系统与 CT 撒布一起安装。该系统在不同的操作中略有不同，但通常包括节流阀、DualFlow、SSV、超级双相管道、多相流量计和控制容器，以实现远程监控。 

该设置是为了使线圈运行能够返回到振动台而准备的。当检测到碳氢化合物时，它会通过闭环固体管理系统重新路由。这确保了平台甲板上不会产生碳氢化合物、NORM、H2S 或苯，并保证海上操作员的安全。CT团队使用的基础油通过上部处理系统输送。

利用实时固体测量与多相流量计相结合，为操作员提供了四相（油、气、水和砂）流的即时回流数据，从而确认了油井生产率。

由于固体管理能够处理 5,000 psi，因此可以使用与 CT 操作相同的系统来进行刺激后流量。这消除了通常花在规划和装配上的时间，以及与手动更换设备相关的 HSE 风险。反过来，这使操作员能够在油井初始回流期间快速实现最佳产量。

在三年的时间里，使用闭环固体管理系统成功清理了九口井。海上运营商或环境没有接触到有害物质。总运行时间达 6,365 小时。其中，<0.01% 或 5 小时被归类为 NPT。分离出超过 200,000 磅的固体，这被认为是成功的。

自动化固体管理系统确保不进行人工处理。作为一个供应商和相同的设备管理 CT 和刺激后流程的固体，规划和操作 HAZOPS 最大限度地减少了成本和时间花费。直流  

By Olof Nilsson and Aksel Skåland, FourPhase

In today’s energy landscape, operators constantly seek solutions that enhance efficiency, minimize environmental impact and maximize well productivity. One such breakthrough is the use of underbalanced coiled-tubing drilling (UBCTD) in combination with closed-loop solids handling systems for sidetrack drilling operations. As sidetracking becomes an increasingly preferred method to access new reservoir zones, understanding the advantages of a closed-loop system in CTD could be the difference between moderate success and optimal well performance. 

CT has been the go-to solution for many of the in-well intervention operations that are normally conducted, both onshore and offshore. It is a versatile tool that can be utilized where a full-scale drilling rig is not required, for operations such as clean-outs, sidetrack drilling, milling, stimulation operations, completion, well logging and diagnostics, perforations, and plug and abandonment (P&A). Common reasons to consider CT include:

• Potential to work with surface pressure: It eliminates the need to “kill” the well, enabling operations under live or underbalanced conditions.
• Minimized formation damage: It avoids the introduction of kill fluids that could impair the formation, thereby maintaining optimal reservoir properties.
• Enhanced HSE: This is achieved through fewer personnel on-site, reduced need for heavy lifting and simplified logistics compared with what is required by a full-sized drilling rig.
• Cost savings: With the reduced labor and equipment needs, CT operations can be more cost-effective than using a traditional drilling rig, particularly for well interventions or smaller drilling projects.

Conventional drilling uses a higher hydrostatic pressure than the reservoir pressure (overbalance). Conversely, if the reservoir pressure is higher than the hydrostatic pressure, it is called underbalance. Underbalanced coiled-tubing milling and drilling operations provide both benefits and challenges compared with conventional drilling.

The utilization of UBCTD presents operators with an opportunity to extract substantial additional value from established reserves and to target multiple reservoir zones in a single trip, enabling the maximization of returns from depleting fields. This is not just a feature but an operational advantage backed by field cases. Research and case studies have shown that UBCTD is efficient in drilling sidetracks. It is associated with reduced formation damage compared with conventional overbalanced methods, making it a validated approach for increased well productivity.

Further, UBCTD allows for the preservation of the natural permeability of the reservoir. This is backed by comparative studies showing increased hydrocarbon recovery rates under underbalanced conditions.

Moreover, CT operations with a dual vessel cyclonic desander enables operation without emissions reaching the atmosphere. This is made possible by creating a closed-loop system using two cyclonic vessels. One cyclonic vessel can continuously produce while any pressure in the other vessel is bled off before solids are emptied. This ensures continuous solids separation and flow from the well and aligns with environmental regulations. 

Applying a closed-loop system has proven successful and beneficial for operators to increase the versatility of their CT operations, as treated seawater, chemicals, nitrogen and base oil or similar can be used during operations. Substances are kept within the system, thus reducing personnel and environment exposure to potentially hazardous substances.

The closed-loop system can be used with both traditional and CT setups. A DualFlow desander system is connected to the flow-tee on the CT riser stack. Typically, a surface safety valve (SSV) is installed upstream from the desander to allow for a quick shutdown. By connecting the desander to the cutting skip with level measurements, the system can be fully enclosed at all times. This ensures no hazardous substances are released into the atmosphere. With a conventional operation, the return is produced to a shaker, and there is risk of operators being exposed to H2S, Benzene and NORM (Naturally Occurring Radioactive Materials).

The ability to design a closed-loop system with a cyclonic desander lies within its automation. The system conducts real-time measurements of the solids separated. By continuously monitoring the weight/volume of separated solids, decisions can be based on operational facts rather than estimates. Additional benefits include:

Interpretation of the solids data alongside the estimated solids calculations provides valuable data to boost the efficiency and quality of CT operations.

Real-time decision making: As the CT operation runs, the solids are tagged, and the cleanout starts. If an expected weight of solids is known, the operation plan can be changed instantly if the volume of solids removed does not match expected results. Steps can then be taken, such as increasing the pumping rate or pulling further out of the hole.

Preventing issues associated with CT getting stuck: CT getting stuck in the well could lead to several scenarios, including loss of operational time, risk of the tool being released in the well where it will need to be fished out or, in the worst case, a shut-in well.

Confidence to operate at optimal speeds: Operators want to run CT as fast as possible. If the data shows that the solids are coming up, operators will have the confidence to proceed at the optimal rate. Using live data in correlation with estimated data can assure and optimize the quality of the CT cleanout. Decisions can be made on the go as the live data is observed. As soon as the data and trends show a clean wellbore, coil can efficiently move to the next step/bite. This can be done with the knowledge that all solids behind the coil tool string are cleaned all the way out of the well.

Ensure a proper cleanout: By analyzing the data in real time, it is possible to verify that the solids are being cleaned out in a scheduled and consistent manner. This means that the closed-loop sand management system topside can handle the solids in an optimum and efficient manner, which translates into economic efficiencies and reduces nonproductive time (NPT). Compact solids plugs can affect separation efficiency. If this happens, all the accumulated sand will be moved out as one compact huge sand plug. This will put pressure on the sand management system, and its efficiency may be reduced. This could lead to sand reaching the process facility.

North Sea case study

To ensure higher production from a field on the Norwegian Continental Shelf, a CT campaign was conducted to clean out stimulated wells over the course of three years. The campaign included eight wells and several stimulated zones. The CT clean-
out was planned to use a mix of nitrogen and base oil to create a lighter fluid column and, therefore, less stress on the reservoir. To avoid any exposure to hazardous substances, including the nitrogen mix, a closed-loop system was necessary. With limited deck space available due to the CT spread onboard, a compact solution for separating the return was sought. In addition, the customer wanted the system to ensure solids-free flow post stimulation.

A FourPhase solids management system was installed together with the CT spread. The system varied slightly from operation to operation but typically included a choke, DualFlow, SSV, Super Duplex pipe, multiphase flowmeter, and a control container to enable remote monitoring. 

The setup was prepared to enable the coil operation to flow their return to the shaker. When hydrocarbons were detected, it was rerouted through the closed-loop solids management system. This ensured no hydrocarbons, NORM, H2S or Benzene were produced to the platform deck and kept the offshore operators safe. The base oil used by CT team was sent through the process system topside.

Utilizing real-time solids measurement in combination with the multiphase flow meter provided the operator with imminent flowback data of the four phases (oil, gas, water and sand) flow, confirming the well production rates.

With the solids management capable of handling 5,000 psi, the same system could be utilized for the post-stimulation flow as was used for the CT operation. This eliminated time typically spent on planning and rigging, as well as HSE risks associated with the manual change of equipment. In turn, this enabled the operator to rapidly achieve optimal production during the initial flow back of the well.

Over the course of three years, nine wells were successfully cleaned out with a closed-loop solids management system. There was no exposure of harmful substances to offshore operators or the environment. Total operational hours amounted to 6,365 hr. Of that total, <0.01% or 5 hr was categorized as NPT. With more than 200,000 lb of solids separated, this was considered a success.

The automated solids management system ensured no manual handling was conducted. As one supplier and the same equipment managed solids for both the CT and the post-stimulation flow, planning and operational HAZOPS minimized cost and time spent.  DC