By ensuring optimal hole size, well designs using solid expandable tubulars have a far-reaching effect on drilling, evaluation, completion and life-of-well solutions. Enventure Global Technology’s Kevin Waddell, Jerry Fritsch and Kristaq Mitrushi discuss the growing influence of solid expandables on well design.
The challenges of offshore exploration and development drilling require that operators – now more than ever – adopt and implement new technology to mitigate risks and ensure success. A major innovation in achieving these objectives is solid expandable technology and its increasing use as a proactive tool in the design of offshore wells – especially in deepwater. In contrast with its roots as a contingency response in extreme wellbores, the emerging role of expandable technology in well designs is aimed at improving drilling efficiency and enhancing evaluation, completion, and long-term productivity.
Instead of a reactive technique for well construction, this planned application focuses on optimizing return on investment. By improving offshore economics, expandable well designs are redefining prospect viability and creating new opportunities for existing assets.
Solid expandable tubulars have a long, successful track record. Over 1,000,000ft of pipe have been reliably expanded in over 1100 installations globally, in land and offshore applications. Successful tool performance in these wells, many with very challenging downhole environments, is 95%.
With this success and continued technology development, expandable applications have grown from contingency applications to planned solutions. For deepwater wells, this is proving to be an exceptional advantage. Solid expandable tubulars are being used to address risks due to borehole instability, improve zonal isolation, and reach target depth with an optimum wellbore diameter.
There is already a high degree of expandable experience in deepwater wells across a range of sizes and applications. Enventure Global Technology has performed 34 installations with an expandable shoe set below 20,000ft – the deepest sitting just shy of 29,000ft. Additionally, expandable liners have been used on rigs water depths in excess of 7000ft and in wellbores with temperatures nearing 400°F. The most common size in these ultra-deep installations is the 95/8 x 113/4in expandable system, but a range of sizes and depths are found globally. This extreme working environment has provided a substantial school of learning. One of the most important subjects: planning.
Planning is important to meet specific well objectives and address unique challenges. But the repercussions of a less-than-optimal hole size constrains many aspects of the well’s success. A smaller wellbore can significantly affect the overall economics of a project. Poor efficiency and degraded capabilities for logging and completion limit asset performance. Reduced production through a restricted wellbore can be a very costly, especially over the life of the well.
An expandable has traditionally been used to address problems when they arise; however, design decisions involving expandables are now being made early in the process to optimally integrate performance characteristics with the geology and well objectives. This helps avoid limiting hole size because of reactive decisions made in the drilling process. Instead, a more holistic approach starts with considering what can be done to ensure optimal hole size while balancing risk and benefit.
Early planning takes advantage of expandable technology’s core value: ensuring the optimal wellbore in the reservoir. In this respect, expandables are very much a facilitating tool for achieving the appropriate completion. The lithology and the reservoir drive planning considerations: how complex is it, what is its potential and how big does the hole need to be?
This doesn’t exclude the value within the actual drilling process. Expandables mitigate problems associated with lengthy openhole exposure caused by efforts to reach a planned casing point, or trying to make up for one already lost. In addition, expandables lower costs by reducing the need for a tie-back, and by eliminating the expense and risk of fighting kick/loss scenarios in narrow pore pressure/fracture gradient windows.
But more wellbore room also directly impacts the hardware used to drill, evaluate, and complete the well. A larger hole improves efficiency by allowing bigger drilling tools that typically drill farther and faster with fewer failures than smaller systems. Hole diameter also has a major role in how the well is evaluated, completed, and maintained.
Size is a significant factor in the capabilities of logging tools and instruments for drill stem tests, vertical seismic profiling, and coring operations. The data acquired from these devices is used to evaluate the well for exploratory, appraisal, and development activities that determine strategies and expenditures of hundreds of millions of dollars.
Over the life of the well, a larger completion provides more options for remedial work. Instead of constructing wells that have limited or no capacity for an economic workover, the larger wellbores achieved with expandables offer new design options for extending the asset’s productive lifespan.
De-risking risk mitigation
Solid expandable tubulars continue to help mitigate the risks and challenges associated with offshore drilling. But implementing a new technology in and of itself can carry its own risks. Over the last decade, solid expandable technology has undergone its own revolutions of sorts – both in operational and technology development.
The first years of expandable installations, usually in exceptionally difficult hole conditions, provided a substantial learning curve. That learning curve created a very effective process for ensuring successful expansion and operation of the expandable system. This process starts with evaluating not only the well in question but the actual goals of that well. For instance, evaluating the full scope of unknown and known wellbore risks may result in a decision to install an expandable higher in the well design. This planning decision ensures that more options exist further down the well if additional casing strings are needed.
Once the well has been evaluated for design considerations, additional well information is gathered to ensure that the operations are within the expandable’s operating parameters. Expandable engineers and operations personnel review and evaluate parameters such as wellbore conditions, mud weight, temperatures, inclination and dogleg severity. If the well parameters are closer to the border-line of the operating envelope, additional evaluations such as torque and drag calculations, and compression forces are performed to evaluate feasibility.
In the next planning step, operations- associated risks are identified and mitigated. For instance, before the expandable system design is generated, all initial risks are identified in a registry, and appropriate preemptive risk mitigation techniques are applied.
An operations installations team then develops detailed job-specific installation procedures. This planning includes all lessons learned from previous similar installations. Then both the risk evaluation and installation procedure are reviewed, discussed and agreed upon with the operator. The operator embeds these risk mitigation techniques and installation procedure into the drilling program.
Over time and through lessons learned, it became apparent that installing an expandable at the last possible moment would always present more risks and create more nonproductive time (NPT). To start with, the well conditions are already less than desirable. Second, the shortness of the planning stage may result in inadequate development of risk mitigation and installation procedures with the operator, which can lead to miscommunication. In these scenarios, the risk of improper judgments on the rig during installation is often higher than necessary.
An operator in the Gulf of Mexico learned this first-hand. Their first exploratory well faced one problem after another without reaching the target objective. In the second attempt, two expandables were included in the design – both contingency. One system was planned for just below the 95/8in casing while the second was installed in the 7in. casing. Even though both expandables were successfully installed, a significant amount of NPT continued to plague the well design. In the third well, one expandable section was planned higher in the wellbore, directly below the 117/8in casing. Then a second expandable was planned as a contingency below the 93/8in casing. Both were installed – at a savings of over $24 million in reduced NPT.
An application that offers the most value almost always is associated with close collaboration between the expandable service provider and the operator’s reservoir engineering and drilling departments. This allows both parties to evaluate the best solution for maximizing return on investment and long-term sustainability of the reservoir.
A better system
Over the past decade, solid expandable systems have been enhanced to provide better drill-out, more robust connections and increased burst and collapse rating. These advances have extended the use of expandables to even more demanding applications.
A 2006 upgrade to the expansion tool dramatically reduced the amount of material drilled out after expansion. Continuing advances in expandable connections are also pushing the envelope of expandable technology application. Most recently, high-performance expandables in 75/8 x 95/8in (4750psi collapse) and 113/4 x 133/8in (3680psi collapse) systems have been developed and installed. The collapse pressures compare to respective collapse pressures of 2650 and 1190 with standard expandable pipe. Both options were developed for offshore applications and have proven value in domestic and international waters.
The first high-performance application was in the North Sea. The goal was to isolate a high-pressure interval to drill the next weaker formation with a lower mud weight. Conserving hole size in the high-pressure interval enabled a successful 5 x 41/2in completion and extended the production life of the well an estimated seven years.
Most recently, an operator sidetracking out of an existing well was left with severely damaged 133/8in casing due to wear. Since the first sidetrack was not able to reach the target depth, a second sidetrack would require a repair to the 133/8in casing. The operator installed a high-performance 113/4 x 133/8in cased-hole liner to reinforce the casing and repair the damaged section. In addition, the operator chose to plan-in a 95/8 x 113/4in openhole liner to extend the shoe lower in the same wellbore. By incorporating both cased-hole and openhole systems, the operator was able to successfully complete the sidetrack and evaluate the target formation.
Risk isn’t always in the form of success or failure. It can often take the form of: high NPT, over-exceeded budgets and AFE, poor reservoir evaluation, and/or a less-than-adequately constructed wellbore resulting in an ID that’s too small at TD. Today, proactive well design using solid expandable tubulars is a central point of success in a growing number of offshore wells. These applications enhance efficiency and productivity by ensuring an optimal hole size that benefits drilling, evaluation, and completions for lifecycle well management. The result is a significant improvement in the economics of exploration and development assets across the globe. OE