Coiled Tubing Sets Packers Precisely During Offshore Well Abandonment
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The complete paper discusses the systematic approach adopted by a service company to achieve the goal of safely abandoning wells offshore southwest Brazil with different completion types using light workover vessels. Having determined the abandonment methodology, service company personnel developed processes and procedures to reach the objective that included advances in coiled-tubing (CT) rigup procedures and use of a real-time telemetry system.
The use of a CT real-time telemetry system enables accurate setting of a through-tubing inflatable device system (T-TIDS) by monitoring the necessary downhole parameters in real time. The paper presents a case study wherein sensors [such as a casing collar locator (CCL) to perform depth correlation before setting the T-TIDS and placing cement plugs, a pressure sensor to monitor the T-TIDS setting, and a CT internal pressure sensor to help ensure all cement was pumped out of the CT] were used in real time to verify that well barriers were set in place, contributing to successful well abandonment. Real-time data collection proved to be the most-effective methodology for running critical equipment, thereby saving overall time and cost.
General Abandonment Requirements
The decision for permanent abandonment of a well is not always easy. In Brazil, the National Agency of Petroleum, Natural Gas, and Biofuels (ANP) has established a compendium of rules for oil companies that extract and produce oil, gas, and derivatives. This involves a group of barriers known as CSB, which is a set of one or more elements with the objective of preventing the unintentional flow of fluids from the formation to the external environment and between intervals in the well considering all possible paths. The CSB’s aim is to guarantee the isolation of intervals with current and future flow potential. Cement or other material with similar performance must be used as barrier elements.
Achieving a unique solution is dependent on having up-to-date information regarding the wellbore diagram, reservoir, history, well location, CT-performance capability, surface equipment, well-control equipment, and proposed layout. Fig. 1 illustrates the design of the 3D wellbore graph generated with modeling software.
The well discussed in this work contains deposits of asphaltene and sand-accumulation debris. For the operator to perform a plug-and-abandon (P&A) intervention, an effective solution to provide reliability safely is necessary to avoid worsening the well condition and delaying the intervention. The service company offered experienced personnel and engineering capabilities, a customized program for job-specific requirements, the CT package, and reliable processes and advantages compared with heavy workover units. Included as part of those advantages is a variety of bottomhole-assembly (BHA) tools that can be deployed in the well with the capability to be customized, working together with wireline operations and the robust management safety system.
T-TIDS are used in applications where the BHA must pass throughout a wellhead restriction or cased-hole restriction and must be installed at inner diameters larger than such restrictions. They can be used as remedial or completion applications. A T-TIDS was used to perform P&A applications in the operations discussed. T-TIDS applications include the following:
- Straddle packer
- Retrievable production packer
- Permanent or retrievable bridge plug
- Cement retainer
Well-temperature variation before and after the T-TIDS installation influences the success of the operation. Once seated, temperature changes also will affect pressure inside the T-TIDS. Increased temperature can lead to overpressure until bursting, while decreased temperature can lead to falling or slipping of the T-TIDS. The pressure gradient is calculated during operational design according to the expansion of the T-TIDS pressure at which it will be installed and the well temperature before and after installation.
The design of service (DOS) is a requirement that helps ensure that the job purpose will be achieved. The DOS is prepared by an operational engineer on the basis of well data (wellbore diagram, reservoir, history, and well location) and an expected solution. The DOS presents topics related to customized intervention operations. Moreover, all BHA tools (including a contingency plan) necessary to perform the operation are included. In case of adjustable parameters during the operation, as per some variation of the well conditions or operator request, one update should be performed with all parties in agreement. The service company used modeling software to help the engineer customize job execution.
The BHA is the tool component conveyed by CT to reach the target and perform the operation. For this operation, it was used in addition to the basic tools such as a CT connector, a double flapper check valve, a disconnector, a rotary jetting tool, telemetry sensors, and the T-TIDS.
The use of a CT real-time telemetry system into the BHA enables accurate T‑TIDS setting through real-time monitoring of the necessary downhole parameters. The sensors used at the BHA in this well included internal/external pressure, temperature, tension-compression, and a CCL. The CCL was used to perform depth correlation before setting the T-TIDS and placing the cement plug with the real-time internal/external pressure signal to monitor T-TIDS setting and managing the CT internal pressure assist to help ensure that all cement was pumped out of the CT.
Sequence of Operations
Before running the CT BHA with the T‑TIDS, a jetting and drift process was used to remove present incrustations inside the production tubing to help ensure successful T-TIDS setting. In this single run, three objectives are achieved in just one trip in/out:
- Jetting the well using a rotary jetting tool. A simulator tool exists that calculates pressure loss per the input-jetting-nozzle configuration and relative pressure effect at the casing hole.
- Drifting the production tubing with a weight bar at least ⅛-in. bigger than the T-TIDS outer diameter. The weight bar simulates the length of the T-TIDS.
- Correlating depth using the CCL sensor to place a mark on the CT at the surface. The mark will be a reference point for a posterior run to set the inflatable packer.
The procedures followed for all eight runs are described in detail in the complete paper.
P&A Success Analysis
During this operation, three CSBs were installed in accordance with ANP regulations. The first CSB inside the 7-in. liner created a barrier between two formations, and two CSBs were constructed at a height of 129 m to act as the main well barriers. The annulus cement was pressure-tested with positive results per the operator report delivered to ANP. Additionally, the CSBs inside the production tubing also were pressure-tested and approved.
The BHA in the first and second run was slim because of the risk of CT becoming stuck in the subsurface safety valve. This approach represents one type of mitigation offered to the operator for customized operation. The slim BHA overcame issues during the operations, such as sticking of CT at a reference point, passing through a restriction, and providing the same assurance for the operation regarding tension/compression capacity.
The next six runs were aided using downhole sensors to determine the exact location of the BHA to position the rotary jetting tool and the cement retainer to meet national regulations. During the entire run, internal/external CT pressure was monitored in real time by a field engineer; in case of abnormal pressure noted while setting the T-TIDS, a contingency plan could be applied on time in conjunction with operator-enabled onsite decision making.
After eight intervention runs in the well using CT, the package was customized per operator request in real-time mode in the field during the operation. The reliable execution process showed operability to P&A per regulations with adherence to all health, safety, and environment policies, one of the more important execution aspects within the industry. The success of this kind of dynamic intervention is the result of careful planning (DOS and simulation), daily BHA-tool maintenance, continuous monitoring of well conditions, and an excellent partnership with the operator in both the field and the office.
Overall, the results obtained with this intervention show that operational time was reduced because of efficient execution of the equipment and process, such as the real-time data-acquisition system, the depth-correlation (CCL) sensor, real-time interpretation of signals during the operation, and efficient T-TIDS setting procedures.
Coiled Tubing Sets Packers Precisely During Offshore Well Abandonment
01 June 2020
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