Coiled tubing (CT) is a long, flexible, metal or composite pipe with no joints that is used in the oil and gas industry for a variety of purposes:
Coiled tubing has several advantages, including increased efficiency, cost effectiveness, and safer operations. Some of its disadvantages include limited depth and borehole size, high maintenance costs, and reduced accuracy. This article describes the operation and applications for coiled tubing units (CTUs), and it specifically covers the well control stack and industry recommended practices for pressure testing coiled tubing.
Coiled tubing units (CTUs) include the following components:
Coiled tubing can be used for drilling operations without the use of drill pipe and a rotary table, which speeds up the process. A bottom hole assembly (BHA) with a drill bit is connected to the coil tubing and inserted in the well. The injector head pushes the tubing into the well and the BHA uses a motor or rotary steerable system that rotates the drill bit. The BHA is essential for directional drilling and wellbore navigation.
A downhole mud motor may also be used in coiled tubing drilling operations to convert the hydraulic energy of the drilling fluid into mechanical energy to rotate the drill bit independently of the coiled tubing string.
Coiled tubing is a beneficial tool for circulation in well interventions due to its continuous length’s ability to navigate complex wellbores. Most often, the operation will involve pumping nitrogen or various fluids to free the well of light debris (sand) and removing water or condensates built up during production.
Coiled tubing allows the deployment of logging tools into the wellbore to collect data about the formation and well conditions, such as formation pressure, fluid composition, temperature and formation properties. This is especially useful in highly deviated or horizontal wells where traditional wireline logging might be challenging.
Subsea lubricators dictate the length of perforating guns that can be run when using conventional drill pipe. Coiled tubing simplifies perforating operations by allowing the use of long bottom hole assemblies (BHA) while maintaining dual well control barriers. This enhances safety and operational efficiency.
Coiled tubing can be connected to pumping units and inserted in a well to pump fluids for various treatments, including well stimulation, hydraulic fracturing, acidizing and cementing. The ability to pump the fluid without interruption while continuously inserting the coiled tubing allows a steady and controlled flow rate.
Coiled tubing can be used for various production enhancement techniques, such as gas lift or artificial lift systems, contributing significantly to improved efficiency and reduced downtime. In gas lift installations, CT enables more efficient and precise placement of gas lift valves along the tubing string, especially in deep or deviated wells. In artificial lift systems, CT significantly reduces installation time for electric submersible pump systems in shallow gas wells to address liquid loading issues.
CT is valued for its flexibility, efficiency, and ability to perform a wide range of tasks without the need for a rig, making it an essential tool in offshore well interventions.
The CT operator in the control cabin manages the entire process of deploying and retrieving the tubing during CT operations. Coiled tubing is spooled off the reel and passes through a tubing counter that measures the length of the tubing being deployed and retrieved. The tubing is then guided through a gooseneck and directed downward to the hydraulically driven injector head, which the CT operator uses to control the movement and depth of the CT string. The tubing becomes straight before it enters the well control surface stack.
Beneath the injector head, the stripper assembly on top of the well control stack provides a dynamic seal around the tubing string, which is crucial for running the CT in and out of live wells.
During intervention operations, CT can be used to circulate acid, nitrogen or cement. Devices may also be conveyed down the tubing for purposes such as sealing, cleaning, or initiating other downhole operations. For example, balls may be pumped down the tubing to isolate sections of the well, or darts may be used to trigger tools and other chemical treatments. The CTU uses hydraulic pressure to push these devices down the tubing and through a dual-flapper check valve. The flow of hydraulic fluid is carefully controlled to ensure the devices travel to reach their target accurately. Coil tubing also allows logging tools to be deployed down the wellbore to collect data about the formation and well conditions. The CT Operator monitors the movement of devices in real time using sensors and telemetry systems.
At the end of the operation, the tubing is pulled out of the well and spooled back onto the reel. A high-pressure swivel joint on the reel hub allows fluid to be pumped while the reel rotates.
Coiled Tubing operations are governed by regulatory standards and recommended practices to ensure safety and efficiency. Key standards and recommended practices are 30 CFR Part 250 Subpart G and API RP 16ST, respectively. 30 CFR Part 250 Subpart G is a mandatory federal regulation for outer continental shelf operations, whereas API RP 16ST is a voluntary industry standard. The recommended practices in API RP 16ST offer detailed guidance to support and enhance compliance with the regulations set forth in 30 CFR part 250 sub part G.
API RP 16ST (Recommended Practice for Coiled Tubing Well Control Equipment Systems) is a crucial standard governing coiled tubing operations. The second edition, along with its Addendum 1 from February 2022, provides updated guidelines for well control equipment systems used in coiled tubing operations to ensure enhanced safety and operational efficiency. A summary of some of the key sections of the recommended practice are listed below.
A coiled tubing (CT) well control barrier is defined as a tested mechanical device, or a combination of devices, designed to prevent the uncontrolled release of wellbore fluids.
Key components include:
This section outlines the recommended order of components in the well control stack from the top down:
1. Stripper Well Control Component
2. Blind Ram Component
3. Shear Ram Component
4. Kill Line Inlet
5. Slip Ram Component
6. Pipe Ram Component
7. Dedicated SBR Component
All well control equipment must undergo pressure testing.
The well control stack plays a critical role in flow control and well control in CTUs by sealing off the wellbore to contain unexpected flow and high pressures during drilling, production, and intervention operations. A typical well control stack used for CT operations is shown below. Actual stack configurations may vary based on the operator and the conditions encountered during coiled tubing operations.
As stated in the API RP 16ST, all well control equipment components should be pressure tested every seven days. The pressure test sequence for each component consists of a low-pressure test, followed by a high-pressure test. A component passes the LP test (from 250 psi to 350 psi) if the pressure stabilizes with no visible leakage for at least five minutes. The component then passes the HP test (MASP plus 500 psig) if the pressure stabilizes with no visual leakage for a minimum of 10 minutes and does not decrease below the intended test pressure. It can take several pressure test attempts to test all of the well control components. The figure below shows the stripper being pressure tested.
It’s common to pressure test multiple tools during a single well control stack test to improve testing efficiency. This is done by testing one tool, disconnecting the assembly, installing a second tool and then reconnecting the assembly. Typically, the test plan will need to include steps after this process that verify the connection point. Similarly, tools that are meant to stop pressure from coming up the coil (dual flapper check valves, wash heads, etc.) will usually need to be verified during the pressure test.
CTUs play a critical role in oilfield operations, providing a range of applications from drilling to interventions. Coiled tubing’s flexibility and efficiency make it a valuable tool for optimizing well performance and maintaining well integrity. For details on IPT’s well integrity solutions, contact us.
IPT Global’s expert advisory services and SureTec® software solutions came together to deliver value to all stakeholders during a well intervention program in Angola, off the west coast of Southern Africa. An intervention services company (ISC) took on an extensive program, with the goal of having its own personnel perform the integrity tests while relying on remote support from IPT Global, including our Field Advisors and Real-Time Operations Center (RTOC). The ISC wanted to demonstrate the ability to provide turnkey intervention services for various operators while performing the tests safely and efficiently to avoid costly non-productive time. IPT Global’s team worked with the ISC to create a custom operational support plan comprising in-house and on-site training, optimization of planning and test execution, and remote support.
IPT Global provided pre-deployment training at its office for the ISC’s engineers and managers. The training focused on using existing test plans to run tests and publish reports. Several variations of the test plans were run using existing schematics. IPT Global provided setup guides for the digital acquisition (DAQ) unit and transducers, along with quick start guides to run various tests in the SureTec platform. The participants were able to experience live data acquisition and testing scenario simulations, allowing them to become familiar with the SureTec PressureTesting with the workflows & procedures.
At the rig site, IPT Global’s Field Advisors trained intervention personnel so they could run SureTec PressureTesting with remote support from our RTOC. The training focused on using PressureTesting’s TestPlanner and TestEngine modules to guide testing efforts, leveraging the RTOC for remote support and publishing tests. IPT Global’s RTOC and engineers helped to manage the testing program with handover and record archival while transitioning between wells.
The operator planned 28 integrity tests, with specific criteria for each of the test types performed. IPT Global engineers created a test matrix for the ISC that included the operator’s criteria and a procedural reference for each test, making review and approval easier. The SureTec TestPlanner matrix also helped ISC personnel manage the testing program by making it easier to locate and run previously built test plans on the testing laptop. This allowed the company to focus on their operations and setting up the hardware rather than having to set up each test plan.
Completed tests and reports were saved in the SureTec platform for archival and traceability. The SureTec Platform is a secure, web-based tool that also provides real-time status of pressure tests, test data organization and retrieval by well and date, advanced data analysis, and remote viewing of active tests.
The ISC received remote support from IPT Global’s RTOC, which is staffed by experienced engineers and advisors who monitor all pressure tests 24/7 and provide global technical support. Remote support ranges from assisting with data connections, networking issues, and basic software issues to advanced support such as:
The intervention program required 28 integrity tests with various operator criteria to be performed over a relatively short period. The ISC successfully executed the intervention program and achieved its primary goal of providing turnkey service with digital software and remote support from IPT Global.
SureTec’s PressureTesting solution provided accuracy, objectivity, and flexibility that assured the integrity of all tested components according to the operator’s criteria. Our engineers performed post-test reviews to ensure all components were tested to the proper pressure as dictated by the operator. And IPT Global Our field advisors verified that test reports were published properly to assure the traceability of all integrity tests for hand-off to the production team and to provide an auditable trail of compliance for local regulatory bodies.
Most importantly, the ISC was able to deliver the intervention program safely to protect people, the environment, assets, and the reputations of all stakeholders.
To learn more about the SureTec platform and our PressureTesting solutions, contact us!
Well Interventions may be performed to add or restore production or to fix a well integrity issue. Expected production gains from deep and ultra-deep subsea wells must justify the cost of offshore intervention vessels and crews. Light well interventions are more common and cost-effective because they can be performed with minimal shut-in of the well. Light well interventions include, but are not limited to, acid stimulation; sand, scale, or hydrate removal; and gas lift remediation. In light well interventions, tools or sensors are lowered into a live well using slickline, wireline, or coiled tubing while pressure is contained at the surface. Service companies can perform light well intervention operations through subsea wellheads using riser or riserless methods while using a ROV to perform the operation and guide the landing of the well intervention equipment as shown in the stimulation example below.
Each intervention program has specific objectives, operational steps, and associated risks. To enhance the safety, reliability, and assurance of the program, IPT offers integrity testing and assurance for a wide range of systems and components.
Subsea well interventions involve many challenges and require comprehensive planning to mitigate risk. IPT’s SureTec application is a single solution that handles all facets of integrity test planning for intervention operations. Interventions require a large number of integrity tests with varying criteria to be performed over a relatively short period. SureTec improves efficiency and project management, and it reduces risks by allowing operators to use consistent and stringent criteria for validating integrity-critical WBEs.
SureTec’s planning tools allow designers to build interactive schematics, wellbore diagrams, and test plan steps for stump, BOP, deck, coil tubing, positive and negative (inflow) test plans. SureTec’s Schematic Editor provides drag-and-drop components that accurately depict the operation of surface and subsea equipment. These schematics are integrated seamlessly into test plans that clearly identify test criteria and precisely simulate valve states and pressurized paths as shown in the following figure.
IPT’s support includes a Real-Time Operation Center (RTOC) staffed by engineers and experienced advisors (RTOAs). Our engineers assist operators and intervention service companies by building test plans in SureTec that accurately represent their testing program. An engineering team member can also create a test matrix that provides a snapshot of all tests and criteria as well as guidelines that help the production and intervention crews with hardware setup. Our RTOAs are responsible for reviewing intervention test plans to ensure all critical components are tested to the appropriate pressure.
IPT’s support includes a Real-Time Operation Center (RTOC) staffed by engineers and our Field Our Field Service Quality Advisors (FSQAs) or trained intervention service company personnel use SureTec to perform pre-deployment activity testing of the well intervention equipment, the manifold, and other surface iron to assure that the intervention tools and well control components work properly prior to their deployment on the vessel. SureTec provides component integrity assurance with high digital resolution and stringent test criteria. Digital resolution and sensor accuracy are vital because high measurement sensitivity is required to detect small pressure changes in control lines, and small-volume cavities and annular spaces.
Upon the vessel’s arrival at the well, our FSQAs or trained rig crew use SureTec to ensure the integrity of the system that will connect to the well as this system will protect people, equipment, and the environment during the latch up phase.
During installation on the seafloor, the tree cap is removed, and the well stimulation tool is connected (latched) to the subsea tree. After the well access tool is latched up (e.g., a stimulation tool), IPT performs a connector test to verify the integrity of the system.
During intervention operations, integrity tests must be performed thoroughly and efficiently because any avoidable delay in critical path operations can increase risk and be costly for both the intervention service company and the operator. Efficient testing of critical components requires the ability to connect to various sources and run multiple tests simultaneously. SureTec receives data from multiple sources such as the IPT transducer, ROV transducer, ROV control system, and Workover Control System. Users can enter Multi-Test mode to execute up to four test plans simultaneously, each with a different pressure source and test criteria. Users can start, stop, and restart analysis for each test independently.
After the intervention is completed, the operator also needs traceability of all integrity tests to hand off to the production team and to have an auditable trail of compliance with local regulatory bodies. When each test is completed or stopped, SureTec generates a standardized, detailed report of each test step, including pressure graphs, schematics, and complete documentation of tested components. Our RTOAs review the test files to ensure all tests passed and all components were tested to proper pressures. They also verify the integrity of barriers before the intervention team departs.
The documented data and lessons learned from each intervention fosters an environment of continuous improvement and delivers the highest-level integrity assurance to operators, production operations, and intervention service companies.
Operators’ intervention and production teams can use IPT’s SureView application for report archival and traceability over the entire lifecycle of the well. SureView is a secure, web-based tool that provides real-time status of pressure tests, test data organization and retrieval by well and date, advanced data analysis, and remote viewing of active tests. SureView’s interactive search features simplify retrieval of historical test data for review and analysis.
IPT’s comprehensive planning, test execution, and reporting tools combined with our team of experts contribute to better management and mitigation of potential risks leading to improved performance and greater assurance of well integrity during well interventions. Contact us to discuss your well interventions.
Technological advances in offshore drilling have aided in overcoming well intervention challenges, increasing the number and total depth of wells drilled in deep and ultra-deep water. Drilling in deeper water and at greater depths increases operators’ risk and reduces the margin of error regarding the protection of people and the environment. During drilling and completion of wells, IPT provides products and services that help assure well integrity and avoid well interventions to repair critical well components. However, as the number and age of deepwater wells increase, the need for interventions increases as well due to the onset of other conditions like sand production, corrosion, hydrates, scale, mechanical failure, and water influx. Each intervention is costly, and its outcome is uncertain. When interventions are necessary, IPT’s products and services also provide well integrity assurance.
Learn the risks and challenges faced by operators and intervention service companies when the decision is made to repair damaged or underperforming deepwater wells.
A well intervention involves taking the well offline and breaking the primary barrier of the subsea infrastructure and potentially the secondary barrier as well. The subsea infrastructure may have degraded after years on the sea floor. A single intervention costs millions of dollars and the cause of the well problem may not be completely known when the intervention process starts. Therefore, re-entering a previously secure well in extreme conditions introduces additional risk to people, the environment, assets, and the operator’s reputation.
When intervention becomes necessary, the operator is focused on managing the cost of reestablishing production while maintaining safety and regulatory compliance. The cost and complexity of interventions are directly proportional to water depth as it determines the size of the intervention vessel and crew required. The intervention crew typically visits multiple well locations for various operators on a single tour to maximize the operational functionality of the vessel. Although this complicates scheduling of the vessel, it allows the cost of intervention services to be split across operators, reduces the travel time to each well, and minimizes port and duty costs.
Due to cost and scheduling complexity, operators want to avoid repeating the intervention process and suffering lost production again for a given well. The operators want to ensure the intervention tools and well control components work properly prior to connecting to the well. After the intervention, the operator also needs traceability of all integrity tests to hand off to the production team and to have an auditable trail of compliance for local regulatory bodies.
Integrity testing of well components during interventions presents different challenges as opposed to testing during well construction. An intervention may only last a couple of weeks, so component integrity tests are performed more frequently than during well construction. Many offline integrity tests are performed simultaneously on the deck of the intervention vessel to eliminate delays once the crew connects to the well. During intervention, integrity tests must be performed thoroughly and efficiently because any avoidable delay in critical path operations would be costly for both the intervention service company and the operator. The final test in the intervention process is the inflow (negative) test on the surface-controlled subsurface safety valve (SCSSV), a critical component that provides fail-safe closure to prevent uncontrolled flow in the case of catastrophic damage to wellhead equipment. A major challenge in the industry has been the lack of consistent test criteria by which to determine if the final inflow test passes or fails. This leads to inconsistent test results across rigs.
Post intervention, communication between the intervention service company and the production operations crew about the status of the well and the integrity of the well components is critical to a successful handover. Many problems and accidents have occurred due to poor handover documentation or communication. The intervention service company must provide accurate and comprehensive reports to all stakeholders.
IPT’s products and services perform and track integrity tests on well components, ensuring transparency during handover between intervention and production stages, and providing an auditable trail should any forensic work be required. Contact us to learn more about how IPT’s products and services assure the success of well interventions.