Wireline Jars

What are they and why use them?

Despite the emergence of Logging While Drilling (LWD) technologies, wireline operations are an important means of acquiring subsurface data, which is often essential for meeting an operator’s field development objectives. Whilst LWD has provided a giant leap forward in the world of formation evaluation and associated data acquisition, it doesn’t always match the resolution, quality, or cost-effectiveness of certain wireline services, notable examples would include (but not limited to) formation testing, fluid sampling, and coring.

A significant challenge in wireline operations is the risk of a toolstring becoming stuck in the wellbore, a ‘Fish’, which cannot be freed within the maximum pull force from the surface equipment and wireline cable. To mitigate such risks, various technologies, including open-hole wireline jars are employed. Jars can provide an insurance policy against getting stuck and the costly job of retrieving a wireline toolstring to surface (a job that may not always be successful).

Jars are utilised to deliver a sudden impact force downhole to assist in freeing the stuck toolstring. A jar integrates two main components which are the “hammer” and the “anvil.” The hammer, which slides and generates the impact force, is located above the jar and the anvil is connected to the stuck point. When the hammer and anvil collide, it creates a shockwave that is transmitted to the sticking point, resulting in subsequent reverberations known as impulse. A high impact and long impulse provide the best chance of freeing the stuck tool (Ref).

There are numerous types of wireline jars available on the market. This article highlights the differences between three variations of open-hole jars, including Halliburton’s LockJar®, Impact Selector’s SMFT™, and SMART™ Jars.

1. The Impact Selector SMFT™ (Multiconductor) jar (Link) activates instantly when the tension transmitted to the jar via the wireline cable, exceeds a preset threshold, delivering a spring loaded forceful impulse, to dislodge a stuck toolsring. Its settings, adjustable at surface by the engineer at the wellsite prior to running-in-hole, and the ability to reset under its own weight for unlimited activations, make it a useful piece of kit. However, precise pre-setting of the trigger load is critical to ensure effective operation, necessitating careful operation planning and tension modelling. In some cases heavy toolstrings may result in the jar trigger load setting being very close to tool weight in which case the Jars need to be run “uncocked”. The SMFT™ is a through wired tool meaning that wireline tools can be run below them which the electronics protected by an oil-filled chamber. Routine maintenance of this equipment, as with all jars, is key to reducing the probability of the jar interfering with the rest of the toolstring functioning correctly.

Halliburton has designed the LockJar® system (Link) to incorporate the functions of both mechanical and hydraulic jars. The hydraulic system provides one of the main attributes of the LockJar® system so that it can be activated at any load above a predetermined lock load, which increases the maximum force available for impact. Its ability to trigger at any load above a preset value after a waiting period offers an advantage over mechanical jars, where the amount of force which can be transmitted downhole to the jar is limited (due to well geometry, borehole parameters, available pull etc). The LockJar® also incorporates a locking feature to prevent inadvertent jarring and allows the wireline tool to move through tight spots without premature triggering. It can be paired with an enhancer that increases the velocity of the hammer mass to yield a greater impact load than the standard configuration whilst protecting the cable head by defusing any impact load moving upwards (Ref).

3. The SMART™ Jar (Link) from Impact Selector is the most recent evolution in jar technology and introduces enhanced control over jar activation for the mechanical jar, allowing field crews to adjust the activation tension required downhole electronically, even after it has been run below the drill floor. This adaptability provides on-command jarring, optimising operational flexibility and responsiveness to changing downhole conditions. Moreover, the ability to adjust the jar impact force downhole allows for tailored management of stuck situations, minimizing equipment stress and the likelihood of downhole failures.

Technical Advisory

Contemplating the use of wireline jars in upcoming wireline operations?

Our guidance leans towards a proactive consideration of jars for all wireline jobs, viewing them as a contingency resource akin to a  potential “get out of jail card”. However, operators must be mindful of several factors when making the decision to use them:

✅Toolstring Simplicity:– At one&zero we embrace the engineering KISS principle, applying it to toolstring design, recognizing that simplicity enhances reliability. Given that a wireline toolstring operates as a series system, typically with a single telemetry bus, overall reliability is inherently lower than individual component reliability and reliability also decreases with each added element.

Two fundamental lessons emerge from this philosophy:

– Avoid unnecessary modules (“tools”) in the toolstring. A risk/reward assessment needs to be made for each toolstring design. The jar is an additional tool in the string and so is a potential point of failure.

– Ensure each component is in optimal condition and well-maintained.

✅Jar Deployment Risks Acknowledge the potential for the jar or components of the toolstring/conveyance system above the jar to become stuck, which may the transmission of force necessary for jar activation. Strategies to minimize the risk associated with different sticking mechanisms are crucial (stand-off placement/ rollers etc).

Due to the very nature of a jar and its purpose, shock loads are sent through the wireline toolstring when activated. This undoubtedly places additional stress on electrical and mechanical components within the tools. Carefull job planning to reduce the shock loading on tools is advised where the technology allows.

✅Mechanical Jar Settings: For non-adjustable downhole mechanical jars, appropriate activation settings are critical. An excessively low setting might underutilise the cable’s maximum pull before triggering the jars, while a setting too high might prevent jar activation. Balancing these settings is essential, keeping in mind that jar activation can lead to unintended equipment damage, time loss, and potential repair or replacement costs. Rigorous tension modelling and independent verification of that model, are critical for accounting for all well and conveyance system variables.

✅Maintenance: In scenarios where wireline vendors rent jars from third-party providers, maintenance oversight may fall outside direct control of the vendor. Monitoring run and maintenance histories ensures equipment suitability and mitigates risks. Independent verification of the in-house or third party maintenance records provides the confidence that everything has been done to deliver a successful operation.

✅Operator Training and Verification: While third-party providers offer comprehensive equipment training, it’s often the on-site engineer or operator who adjusts the jar force activation settings. Verifying these settings before deployment is essential for operational success.

✅Cost -benefit Analysis: Although jars are likely to be a relatively low cost in relation to other services in the toolstring, a cost-benefit analysis needs to be performed on a case-by-case basis. The sticking risk for any well is dependant on a number of variables, some of which can be modelled, whilst others require a more qualitative analysis. However, if running a jar results in the rest of the toolstring being retrieved without a fishing operation, it will be money well spent.

Closing Remarks

This short article has centred around the topic of jars and their application as an insurance policy to get out of the hole when a wireline toolstring gets stuck. It is important to recognise that wireline conveyance is an integrated system, It encompasses the wireline unit (engine & winch), cable drum, cables, rollers, standoffs, hole finders, and an array of other potential components and accessories. Each element introduces a variable that must be integrated into job design to model and understand the resultant forces. Well geometry, wellbore and formation parameters play a key role in the decision to run some of the various options and understanding how these inputs can be modelled can inform the decison on whether to run jars or not.

Thanks for reading this article, future Tool Tuesday articles will explore some of the areas introduced in this article further, with a view to underscoring their potential collective impact on operating efficiency.

✍If you have had jars get you out of a tight spot, let us know in the comments below.

✍ If you think we have missed any relevant points or details, let us know below.