Economical solution can provide long-term isolation to extend life of well, maximize injection rates while conserving hole size
By Luis Godoy, Weatherford
After multiple cement squeezes in a well in Malaysia failed to isolate a damaged casing section, it appeared that abandonment was likely. As with many aging wells around the world, the decision to restore this wellbore’s integrity was based on economics.
For this offshore well, the difficulty of achieving an effective cement job made the operation appear to be a futile effort. Other solutions, such as conventional liners or straddle packers, were not feasible because valuable hole size would be lost.
To make the remediation effective, two goals had to be achieved. First, the cost of the repair had to be balanced by long-term isolation that significantly extends the well’s life. Second, the solution had to maximize injection rates by conserving as much hole size as possible.
Instead of abandoning the asset, the operator collaborated with Weatherford to deploy an integrated remediation system that allowed them to find the specific issue, prepare the wellbore prior to fixing the issue and recomplete the well to convert it to a water-alternating-gas injection well. This integrated remediation approach, which includes expandable cased-hole liners, is finding increasing favor across a range of global remediation applications.
For the Malaysia well, installation of 69 ft of an expandable cased-hole liner provided a reliable, long-term means of restoring wellbore integrity with minimal loss of inside diameter. Performed on a single trip, the installation conserved hole size with a 7.90-in. post-expansion ID and 7.775-in. drift. Successful isolation of the problem section was confirmed with a post-installation pressure test to 3,000 psi. As a result, the injection well was restored to optimal service condition and given a new, long-term lease on life.
A global solution
The economic and operational challenges and results from the Malaysian casing remediation are much the same as applications in others parts of the world. Onshore and offshore, in producing and injection wells, expandable liner systems are being used to address a variety of critical remedial challenges, such as corroded or damaged casing, water shut-off and sealing off old perforations.
With the increasing number of mature fields and the growing risk and complexity of developing new oil and gas reserves, operators are looking for more effective and cost-efficient remediation solutions to maximize production from existing assets.
With an integrated remediation approach, restoring productivity often makes economic sense. The cost of remediation to return an asset to its optimal production is typically an easily supported expenditure when considering life-of-well productivity (Figure 1).
The development and use of expandable liners is a significant contributor to this growing trend and is resulting in a second look at mature fields that might otherwise have been abandoned. In these wells, expandable cased-hole liners are helping to improve performance by restoring wellbore integrity and maximizing reservoir output. Applied as part of an integrated remediation system, the technology is achieving significant success in restoring long-term casing integrity that reduces intervention costs and extends recovery.
Compared with cement squeezes or straddle packers and conventional liners, the expandable liner can be a more reliable and cost-effective tool for restoring casing integrity.
Single-trip installation without the shoe drillout required with a conventional liner significantly reduces rig time and NPT. Typically, expandable liners are installed in one to two days, allowing the operator to immediately test the well and return it to production.
Completions, production and future interventions are optimized because the expandable liner conserves hole size to provide the largest possible wellbore ID. Conventional liners and packer methods are often limited or unacceptable because this valuable hole size is lost. The smaller ID constrains the completion and ensuing production and reduces options in future production optimization efforts.
Using straddle packers to isolate a casing problem can reduce ID even more than a conventional liner. While the straddle packers can be removed to allow work deeper in the well, they provide only temporary isolation, not a permanent solution, and they do so at the cost of severely limiting ID.
In 4 ½-in. and 5 ½-in. cased holes, expandable liners provide a permanent remediation option in smaller diameters where a standard liner is not a viable alternative. Further, while conventional liners are cost-effective over long intervals measured in thousands of feet, expandable liners can be more cost-effective for shorter sections with specific casing repair and isolation problems.
The other common remediation method, a cement squeeze, can produce unpredictable results and expose the formation to high-pressure risks. Ultimately, it is more of a short-term treatment that will require repeated interventions throughout the well’s remaining life.
A comparison of conventional cement squeeze and solid expandable cased-hole liner costs illustrates the relative economics. In a study of casing remediation methods, the authors found that when considering days versus cost, the total outlay of a single squeeze operation is nearly $225,000, accounting for nine total days from the time the rig is moved on location until the well is back on production (Farley, SPE 159685).
Using the same base costs from an East Texas job, it was determined that using a solid expandable liner saved an average of three days while incurring 36% less in associated costs. Another cost factor is that cement squeezes are often not successful on the first attempt. A second squeeze in the same operation could increase costs to nearly $291,000 and add two more days of rig time. The fixed cost of a solid expandable cased-hole liner could cut those costs in half.
Remediation cycle process
The operator uses the expandable liner as part of an integrated process that locates the problem, prepares the wellbore, fixes the casing and recompletes the well. It requires no cement and applies no pressure to the formation during the installation process. The process has a history of success in repairing and remediating common problems.
The method first employs cased-hole wireline logs to precisely locate problems with casing, water production sources, wellbore obstructions and bypassed production zones. These logs include advanced imaging and multisensory caliper tools used to locate internal and external defects caused by corrosion, scale, wear and failure.
Once the problem is identified, the wellbore is prepared for remediation based on the specific conditions. A variety of clean-out mills, such as junk, taper or watermelon mills and other tools, may be deployed to provide a clear path for running the expandable liner. Chemical, hydraulic or other mechanical methods also can be applied prior to the liner installation.
The actual remediation step involves installation of an expandable cased-hole liner to cover the problem area. The liners can be run in short and long lengths to precisely cover target intervals. They are installed in a single trip and require no cement or shoe drill-out (Figure 2).
Once casing integrity is restored, a variety of cased-hole completion services are applied to install packers, frac plugs and artificial lift.
Perforation isolation in the Middle East
In northern Iraq, developing new production from an existing well first required isolation of two perforated intervals in the 9 5/8-in. casing. The remediation had to minimize the loss of inside diameter and provide good economics with long-term isolation. It was also important that planned well tests avoid inducing communication across the old zones.
To meet the objectives, the wellbore was prepared using cleaning equipment, including casing scrapers and brushes, and a junk mill. Once the casing was prepared, two 7 5/8-in. x 9 5/8-in. expandable cased-hole liners were installed across the two sets of perforations. The lower perforation interval of 39.3 ft was isolated with a 110.8-ft liner, and the upper perforation interval of 13.1 ft was isolated with a 35.1-ft liner. Hole size was conserved with a post-expansion drift of 7.475 in. for a 7.60-in. ID.
Each installation was performed in a single trip, and, unlike a conventional liner, no shoe drill-out was required. The total operation, including the cleaning run to prepare the casing interior, took 29 hrs.
Africa casing corrosion
Corroded casing and water flow in a shallow well offshore Congo presented multiple challenges. First, it was critical to find a remediation method that was economical in the context of the mature field. Operationally, the remediation had to contend with platform deck space and weight limitations that prevented the use of a workover rig. The presence of H2S further complicated the remediation.
The corrosion and source of the water flow was first located with wireline services. Prior to installing an expandable liner system, the casing was prepared using fishing and wellbore cleaning services.
Weatherford worked with the operator to develop an H2S-resistant 5 ½-in. x 7-in., 29 lb/ft expandable liner. The liner covered a corroded interval between 820 ft and 1,312 ft to provide a long-term, stable and cost-effective remediation that brought the well up to full integrity.
Instead of a workover rig, a jacking system and specialized equipment were used to overcome platform limitations and run the liner. The single-trip installation provided a post-expansion drift of 5.265 in. to optimize the completion and production. Water production was eliminated, and the well was put on production at 250 bbl/day of oil.
South America seal-off
In an onshore S-type well near Santander, Colombia, watered-out intervals led to installation of a 55-ft, 5 ½-in., 17 lb/ft expandable liner in the wellbore’s existing 7–in., 29 lb/ft casing. The objective was to improve production capacity by sealing off upper water-producing perforations and recomplete deeper in the well.
To optimize the completion and future production, it was important that the remediation minimize the loss of internal diameter. The expandable cased-hole liner resulted in a reduction of only 0.79 in. The inner diameter of the expanded system was 5.39 in., allowing a drift diameter of 5.265 in.
Due to the tubing overpull and workover equipment limitations, the expansion was performed hydraulically in stages using a setting tool. The pipe was successfully expanded and pressure-tested to confirm restored integrity.
US refracs and integrity
An operator in New Mexico needed to cost effectively cover and isolate perforations in 5 ½-in., 15.5-lb production casing to seal off watered-out zones and enable the stimulation of new intervals.
For this well remediation, the process included preparing the casing interior, installing the expandable liner to isolate the perforations and supporting the completion with specialized equipment.
A 4 ¼-in. x 5 ½-in. expandable liner with a post-expanded length of 700 ft was installed in the target interval at approximately 5,000 ft. The installation covered and isolated the upper perforations so that newer intervals could be fractured at 5,500 psi.
The permanent liner provided an economical solution that eliminated the need for multiple cement squeeze operations. Unlike a conventional liner, the expandable liner maximized the retained hole size for optimal production and to facilitate future well intervention. A unique composite frac plug was used to allow the operator to set back inside 5.5-in. parent casing after passing through the installed expandable liner.
In a North Dakota well, multiple cement squeezes had failed to mitigate corrosion leaks in 7-in., 26 lb/ft casing. Running conventional casing significantly limited the wellbore ID. To re-establish casing integrity, an integrated remediation process was applied.
The wellbore was cleaned, and Weatherford’s wireline multi-sensor caliper tool was run to identify the extent of damage and determine the best remedy. TotalView visualization software processed the caliper data to identify casing restrictions, assess drift ID and determine casing damage. The analysis identified severe damage across the 150-ft section, and a 5 ½-in., 17 lb/ft expandable liner was installed.
The cased-hole remediation provided a long-term, cost-effective means of restoring casing integrity in the wellbore. The solution brought the well to full integrity standards in less than two weeks.
In the midst of a fully developed infrastructure, aging wells around the world represent a tremendous opportunity for operators. These wells typically face age-related casing integrity problems that are critical constraints to their ongoing operations. For many of these wells, conventional remediation techniques, such as cement squeezes, straddle packers and conventional liners, present hurdles to cost-effective remediation. An integrated remediation system that includes expandable liners provides an option that is returning wellbores to service and changing the productive outlook for thousands of wells.