There are several reasons to place a cement plug – from plugging the well back for a sidetrack, preparing for a kickoff, well abandonment, or for curing a lost circulation zone. Successful cement plugs are rarely quick or easy. Placing a cement plug in an open hole horizontal well is especially difficult. Additionally, as most open hole plugging operations are unplanned, it’s essential that nonproductive time is minimized and that drilling gets back on track as soon as possible.
In a technical paper published by the Society of Petroleum Engineers (SPE 113092*) the authors found that an average of 2.4 attempts are necessary to achieve a successful sidetrack. With each plug attempt consuming between 24 and 48 hours of rig time, well costs can increase dramatically. Among the problems identified as factor of plug failure include: plug slippage, plug or slurry contamination, and insufficient cement wait time before attempting to drill the plug.
Common practice in setting a plug in open hole is to use a workstring to place a cement slurry, forming a plug and wellbore seal. The workstring is tripped into the desired depth to the bottom of the plug, then a cement slurry is pumped down the workstring and into the annulus between the workstring and the wellbore. The workstring is then tripped out leaving the cement slurry to harden, thereby forming the seal. However, in horizontal wells, as the workstring is pulled through the slurry, the slurry often is pulled uphole, resulting in stringers of cement and a less-than-competent plug.
Determining the correct slurry transition time from liquid to solid is challenging. If the slurry hardens too fast, the workstring could become stuck in the wellbore. If it doesn’t harden fast enough, the plug could become contaminated or move as the workstring is pulled due to wellbore swabbing. Additionally, a slow-setting slurry can slump in the horizontal wellbore, thereby preventing the plug from properly isolating the wellbore and zone.
To solve this problem, plug placement aids have been developed that allow sacrificial tubing to be left downhole at the completion of the plug job. This allows the workstring to be disconnected from sacrificial tubing at the top of the cement plug and tripped out without disturbing the slurry, and without worry that the workstring may become stuck. These tools also allow longer plug lengths to be pumped at the same time rather than setting multiple short-length plugs on top of one another. Additionally, higher performing cement slurries can be used with much faster cure times, higher viscosities, and higher yield points.
These mechanical devices typically employ a wiper dart that is pumped down the workstring which latches into the disconnect assembly when cement is fully displaced. This creates a pressure increase which activates a sliding sleeve, allowing the disconnect to take place. The tailpipe can be made of drillable composite material, and can be drilled out along with the cement plug if continuing operations are required.
However, no mechanical device is trouble free and fully dependable in deviated wells or short plug lengths where sufficient tailpipe weight is not available to assist with separation. What if the required overpull to disconnect is greater than the sacrificial string weight? Do you wait to achieve cement gel strength to pull against? Do you risk pulling on the cement plug? While the industry has been accepting of this potential failure mode in the tool design, Citadel Casing Solutions recognized this shortcoming and engineered a solution.
The PreNup™ Plug Placement aid is run in hole on drill pipe or tubing with sacrificial tail pipe below.
After being released by a dart, the drill pipe is free to be removed from the well, leaving the tailpipe and a formidable cement plug behind.
Citadel’s PreNup™ line of plug placement aids make complicated separations a thing of the past. The tool includes a pump-off feature that enables hydraulic disconnect with the sacrificial tailpipe by applying pressure rather than overpull from surface. This feature eliminates the risk and anxiety of moving the sacrificial tailpipe through the cement plug, or failing to release entirely during release operations. Now cement plug setting can be accomplished accurately and efficiently on the first attempt. Protect the assets you’ve worked hard for with the PreNup™ Plug Placement Aid.
*Al-Yami et al., 2008. New Cement Systems Developed for Sidetrack Drilling. SPE-113092-MS
About Citadel Casing Solutions
Citadel Casing Solutions produces innovative technology for cementing casing equipment.
We create customer value through our unmatched engineering expertise, broad base of experience, and overall responsiveness. Our goal is to deliver the ultimate in wellbore integrity to protect our customer’s assets.
For more information on our PreNup™ plug placement aids, visit us at www.casingequipment.com or email us at firstname.lastname@example.org
Apply Lok-N-Load™ thread lock compound from Citadel Casing Solutions to your casing, tubing, or drill pipe and be rest assured you’re ready to run and gun downhole. Lok-N-Load keeps joints from loosening while running casing or drilling through the shoe-track, and replaces welding on the bottom of casing joints. A Lok-N-Load kit contains a two-part epoxy (base resin + catalyst), along with a putty knife and instructions for use.
Using a PDC bit to drill through downhole components used in the cementing process is always challenging. From drilling the float collar, through the shoe track, and through the shoe, the objective is to get it drilled as fast as possible while inflicting the least amount of damage to the drill bit. Harder materials take longer to drill, and tend to damage bits before they can drill new formation. The challenge for drillable equipment is maximizing strength and durability while reducing drilling time and bit wear.
When designing drillable products, the engineers at Citadel Casing Solutions took advantage of engineered plastics and composites as a substitute for aluminum and cast iron components of legacy systems. The result is a line of equipment that is easy on PDC bits and drills faster, eliminating the need of a clean out trip, and enabling faster ROP through the next hole section. Citadel’s composite components employ a design that meets the stringent requirements for well integrity and downhole performance, yet facilitates drillout without risking bit damage.
The Citadel engineering team is tackling the innovation challenge head on with new and different products for the Casing Equipment and Cementing Tools market. For each of these product challenges, the market has offered solutions for years. Standardization has developed among competitors to the point where each can be categorized as commodity product – with little difference among each player, resulting in price emerging as the only real buying factor that is considered. Our Citadel engineering team is bringing a fresh perspective to these products and strives to deliver a better solution to help our customers improve operational success.
For everything we design, we ask the question – Why leave something downhole when you don’t need to?
At Citadel, the engineering team seized an opportunity to design equipment to include more components that are recoverable at surface, with fewer components that remain downhole after cementing operations are complete. In some designs, the Citadel team eliminated complex machined components from the top-level assembly, again reducing manufacturing and assembly costs, while improving reliability of the product by reducing potential failure mechanisms.
If you can reuse a component, you don’t have to manufacture it again. This results in lower costs and better product availability for our customers. It also improves manufacturing lead time.
At Citadel, our technology organization is comprised of skilled and innovative engineers who have a combined industry experience of more than 45 years. We are tackling the innovation challenge head on with new and different products for the Casing Equipment and Cementing Tool market. Our team of engineers has been awarded more than 70 patents representing numerous disruptive technologies and solutions. They are immersed in a company culture that gives them the freedom to focus on solutions designed for use at the wellsite. This experienced team, along with the culture of innovation, provides Citadel with unique capabilities that are simply not found in other organizations.
In the world of Computer Numerical Controlled (CNC) machining, the objective of designing for manufacturability is to create components at a lower cost and for easier assembly. Cost of CNC manufacturing is driven by time, so to lower machining costs, time must be reduced for certain machining functions. This includes reducing the number of operations, the set-up time required for each, and the type and amount of material that must be removed from the raw bar stock or tube to achieve the finished component.
The Design for Manufacturability process can be reduced to five essential focus areas:
- COMPONENTS: Reduce the total number of parts so that there are fewer items to machine, purchase, inventory, process and assemble.
- MODULAR DESIGN: Utilize a modular design to simplify the testing and inspection processes, along with improving maintenance and service.
- STANDARD PARTS: If purchase parts can be limited to off-the-shelf components, the purchase price can be lowered and lead times can be shortened.
- MULTI-PURPOSE: Parts that are multi-functional reduce the total number of parts required, and help drive down manufacturing costs.
- SIMPLICITY: Keeping fabrication and assembly simple means reducing processes or design requirements that add little value to the usability and function of the product. Examples may be a design that calls for excessively tight tolerances or one that requires a surface finish that is smoother than necessary.
The final cost of a product is directly proportional to the number of parts. Reducing the number of parts increases product quality and reliability. The total number of parts in a product is a key indicator of design quality.
By designing new products from the ground up, the engineering team at Citadel is taking a fresh look at improving efficiency in all designs and processes. Component geometries can be designed for speed, tested for functionality and qualified for dependability.
An example is the groove that is required in float equipment to hold cement in place. The team at Citadel performed trial testing on seven groove designs and geometries to find the optimal configuration that resulted in the least amount of machining time, yet still met all required specifications. They were not tied to a fixed groove design or configuration that had been developed years ago, or a design that must continue to be utilized in its current form to satisfy internal requirements for product line consistency.
At Citadel Casing Solutions, our goal is to revitalize the casing equipment sector, delivering the ultimate in wellbore integrity with the most innovative and progressive tools and downhole products. We live in an engineering-based culture where customer needs come first. We thrive on designing elegant products, solving downhole challenges, and improving our customer’s operational success.