The secure placement of tools and accessories along well construction and completion strings is essential to executing downhole applications.
In wellbore cementing, for example, job success depends on efficient mud removal and cement displacement around the tubular. Both of these objectives may be compromised if channeling occurs, where the cement does not spread evenly in all directions. Prevention of channeling depends on designing the right cementing program, which includes achieving the optimal standoff between the string being cemented and the open hole.
Selecting the right centralizers and planning their location along the string are critical to achieving standoff. And securing the centralizers to keep them from sliding along the pipe is also essential to prevent damage to the string and the risk of leaving junk in the hole if the string must be removed from the wellbore.
A new attachment system designed for simplicity, reliability, and ease of installation has been developed by Ace Oil Tools to overcome the limitations of traditional methods used to secure tools and accessories to drilling and completion strings.
The patented design includes slim-profile male and female collars that are slid onto API casing joints and pressed together with a lightweight machine. As they are pressed together, corresponding ramps work to engage slip wickers to the joint to produce a very high holding force while maintaining a slim profile. The collars also feature a ratchet mechanism to prevent them from coming apart, forming a permanent lock to the joint.
Current Industry Practices
Historically, the most common method for holding casing equipment in place has been to use stop collars that are secured to the liner with set screws. These simple, inexpensive tools are used when only a low holding force is needed and their relatively high profile does not prevent the string from passing through restrictions.
This type of stop collar is not typically suitable for critical wells or in drilling programs that use semi-flush or flush-joint connections. If the collar fails, there are no couplings within the string to push accessories past restrictions, possibly preventing the string from reaching total depth. Collar failure can also result in suboptimal standoff, pipe damage, and junk left in the hole.
As the offshore drilling industry evolved, centralizer subs were developed as a more reliable solution. These short tubulars are threaded into the string between joints. Subs contain machined profiles to interface with the centralizers to prevent them from sliding along the string as they are run into the wellbore. Because the profiles are integral to the sub, they will not fail under high loads.
Some of the issues with centralizer subs are their high expense and the limitations they impose on string design. Only one centralizer per joint can be run, and it can only be placed in a suboptimal location between the joints.
The application-specific design of each sub based on string size, weight, grade, and thread means that subs are custom-built and limited to specific string designs. For this reason subs are very expensive, not only on an up-front basis but in the costs of inventory management and scrapping unused product. Additionally, procurement usually requires long lead times.
Recently, direct-application materials have entered the marketplace. They are applied to the pipe to perform as either a solid-body centralizer or a stop collar. Because they are directly applied, their performance relies on variables such as satisfactory surface preparation, atmospheric conditions, and the installation team’s adherence to correct application procedures. Limitations on bottomhole temperature and temperature fluctuations during run-in operations may also restrict their use.
Centralizers that are crimped onto the pipe are also available. While installation is easy, the centralizers only come in solid-body form. Their placement is typically close to the end of the joint so the crimped area can be gauged to ensure the crimp has not created an internal restriction.
New Attachment System
To date, the new attachment system is featured on three types of tools that have been designed for use on all joint sizes and grades.
The Ace Ratchet Collar (ARC), shown in Fig. 1 above, performs as a stop collar to hold both solid-body and bow-spring centralizers or other accessories on the liner. The Ace Drilling Centralizer (ADC) is a rotating, solid-body centralizer for use in casing and liner drilling. The Ace Tracer Carrier (ATC) houses and protects tracer elements conveyed into the wellbore on the production string.
The simple design of the ARC, ADC, and ATC does not affect the inside diameter of the liner during installation and does not require added connections that pose potential leak paths. The tool designs provide enough clearance to be used in close-tolerance wells. Each collar’s one-piece design completely encircles the joint, having no welds or seams that could break and lead to stuck pipe and/or junk in the hole.
All three tools mount to the outside of the casing or liner, allowing the operator to plan accessory locations anywhere along the joint and run multiple accessories per joint where needed.
Because each tool is fully independent of weight, grade, and thread, they are versatile. Thus, a large range of applications can be met from a small inventory, reducing the burden of inventory management and the risk of having to scrap unused hardware. Furthermore, the tools can be installed with a few hours’ notice. An operator can make final decisions on a centralizer program within days of a planned string deployment.
There are additional tools into which the attachment design can be incorporated. The system can be used on tools or accessories for virtually any drilling or completion application.
The installation kit consists of a hand-held press (Fig. 2) and a small hydraulic power unit. The lightweight installation tool can be handled by a two-person team, allowing installation to be carried out at virtually any location without mobilizing the pipe.
Case Studies
ARC. A major operator drilling an exploration well at 11,250-ft water depth in a remote South American location planned a 13⅝-in. casing string through 17⅞-in. casing with a 16-in. open hole below. With poor wellbore conditions, there were contingency plans to run a 16-in. liner. Normally, hardware for two separate centralization regimens would have been necessary to optimize the standoff of the 13⅝-in. string, depending on the presence of the contingency liner.
Upon determining that the contingency liner was not needed, a two-person crew was sent to the pipe yard to install the ARCs and centralizers in an 8-hour shift. The 13⅝-in. pipe was delivered to the rig, run to total depth of almost 16,000 ft, and cemented without issues. This flexibility saved the operator the cost of having two sets of centralizer subs on hand and led to savings of well costs into six figures.
ADC. The solid-body rotating centralizer, the most recently developed of the three tools, provides an internal bearing to eliminate wear on the liner and reduce downhole torque, helping to ensure that the liner can be drilled successfully to planned depth. The tool’s use was proven in a 7-in. liner-drilling application by an operator that drilled a 900‑ft directional interval while rotating the pipe between 30 rev/min and 80 rev/min. A total of 54,000 rotations on the string and ADCs was recorded.
After the interval was drilled, the liner string was pulled for evaluation. Very little wear (<0.004 in.) was recorded on the centralizer/ARC interface and no issues were found with the ADC. The operator has since elected to use this technology on multiple liner-drilling applications in the North Sea.