Well intervention: One tool to rule them all
Fishing operations often require the application of great force downhole, to retrieve hardware or tools that have been unintentionally lost or stuck downhole. With an inherent lack of sophistication characterizing many traditional fishing solutions, and with the diminishing assistance of gravity in horizontal wells, two problems became more prominent in deeper and extended-reach situations. Firstly, getting to the fish, and secondly, recovering items without compounding the issue.
When fishing in traditional vertical wells, the operation relies on gravity to supply the forces downhole to complete the operation. The laws of physics dictate that as the well becomes more horizontal in nature, the gravity force will diminish until it reaches a point where it is ineffectual.
With the prominence of conveyance platforms like the Well Tractor, half the problem was solved, as the e-line-deployed solution easily overcame the limitations of traditional operations in highly deviated wells by driving tools to any target depth. However, traditional pulling and fishing tools were created for vertical use, or fully mechanical applications, leaving the need for a reliable tool to engage with the fish at the business end of the tool string. Another shortcoming of traditional tools is that they often rely on any force applied at surface to be successfully transmitted to the desired point downhole—a task that becomes increasingly difficult, if not impossible, with increasing well deviation.
FILLING A CRUCIAL GAP
There was a gap in the intervention market, as all the traditional pulling and fishing tools were created for vertical, fully mechanical applications. After Welltec created the robotic tractor, the missing link was the tool that engaged with the fish. With that, there are some challenges, such as traditional tools that are made with different pins, or screws that you are meant to shear mechanically by knocking or pulling to create the forces needed to shear those pins and release the tools downhole.
By allowing reliable disconnect of fishing strings or relocating the fish in the well, the electric release fishing tool is designed to improve and simplify fishing operations. The required grapple type, either external or internal, can be easily assembled on the tool by only changing a few parts, Fig. 1. Electrical disconnect can be activated at any time, when required.
Since the development of well tractors, the industry has invested hundreds of millions of dollars in conveyance equipment. All the focus was on the conveyance methodology, but the actual tools at the end of the tractor were still the same mechanical tools that had been developed over 50 years ago. That is where the Wellgrab electronic fishing tool (Fig. 2) comes in. With this technology, one can engage the fish and pull it out without having to rely on pins. Also, if you are stuck in the very object that you are trying to recover, you are not relying on having to shear a pin to get loose.
MEETING THE DIGITAL CHALLENGE
With the entire operation of the oil field now digital, operators can communicate with all their tools—except fishing tools. This creates the juxtaposition of having invested in digital equipment, yet still depending on 50+ years-old technology with low-level feedback, meaning almost full reliance on the experience of a crew when it comes to retrieving lost or stuck items.
Operating on an e-line, the Wellgrab ERFT (Electric Release Fishing Tool, Fig. 2) resolves this issue by utilizing a range of external and internal grapples to match the specific requirement of engaging a downhole fish. Communication with the grapple is supported by a system measuring multiple parameters, all integrated with an actuation device, such as Welltec’s 100K Well Stroker, which can deliver up to 100,000 lbs of force directly where it’s needed: downhole at the exact fishing point. Most traditional tools would be ripped apart under such force, making this solution a first for the oil and gas industry.
These features have proven to be highly beneficial in the field, proving in one case that an available engagement length of just 29 mm was sufficient to retrieve a parted tool string (with a stuck mill bit) with 33,000 lbs of force. In a situation like this, it’s all about optimization, with real-time information on tool performance greatly enhancing operations, enabling tasks to be completed more quickly and efficiently than by conventional means.
The solution is not a single tool, per se; it is more like a platform for multiple tools, creating a single solution, akin to that of a Swiss Army Knife, with multiple applications. All that is required is to change the grapple at the end of the tool (Fig. 1), and this includes plug setting/retrieval options.
SURFACE CONTROL AND THE DATA
As the ultimate fail-safe, a release-on-command electrical signal can be sent to the grapple at any time. In the unlikely event that the signal is lost, and it is not possible to send the release command, the battery back-up system is activated. At this point, an in-built timer starts a countdown, and after a predetermined period—if connection is not re-established—this will issue a command to release the fish. The novel ERFT system provides full control over the ability to release and makes it practically impossible to get stuck or add more fish.
Wellgrab ERFT (Fig. 2) has a bi-directional motor, and when this is run in a standard manner, it is in a passive mode. The bi-directional capability enables the development of new methodologies and new tools, where the motor is utilized to actually engage the fish. In this manner, there is a wealth of feedback available, such as power consumption, and millimetre precision with regards to the positioning of the motor. It is also possible to monitor parameters, such as temperature, as well as movements or vibrations, via an inbuilt accelerometer.
One further attribute that is crucial to safe operations is the battery backup that is integral to the tool. We are often asked what happens if we lose the signal, the tool is engaged, and we are unable to send a release command. The answer is that we can, because we have a battery backup system. If we lose signal and cannot communicate to the tool, there is an in-built timer that starts a countdown, and after a pre-determined period, if connection is not re-established, this will issue a release command, and the fish will be released.
AN EFFECTIVE SOLUTION
In one instance, a Norwegian Continental Shelf operator had a parted tool string with a stuck mill bit that had been left downhole during a scale milling operation. With several complexities to the fishing operation, including the level of required gripping force needed to attack the limited fishing point available on the fish, conventional tools on the market would not be able to complete the job. So, the well was abandoned temporarily. By combining the Wellgrab (Fig. 2) with Welltec's Well Stroker, offering up to 33,000 lbs pulling capability and surface readout (SRO), a more technical approach to fishing was delivered.
The available engagement length of the fish was only 29 mm, but thorough systems integration testing confirmed that the tool would be able to hold the fish while the Well Stroker applied pulling force. Wellgrab presented a sequence of solutions with a broad range of grapples and spears to account for different scenarios regarding the possible outcome; special emphasis was made on several contingency solutions, in case the fish parted during the operation.
Other complexities, such as wellbore fill, deviation and alignment of the fish were identified and mitigated as part of a special risk assessment, whereupon adjustments were made to optimise correct engagement of the tool onto the fish. First, debris was removed from the wellbore over several runs, using Welltec´s Well Cleaner with Reverse Circulating Bit (RCB), Power Suction Tool (PST) and Heavy Debris Removal (HDR). Access to the fish was confirmed by running a lead impression block, where the top of the fish was clearly visible.
On the fishing run itself, the first attempt revealed a bent finger on the grapple, which indicated access to the fish but a limited wellbore internal diameter. After modelling the findings, the outside diameter of the bell guide was machined down, to allow the tool to access the fish. Following this simple adjustment, the Wellgrab (Fig. 2) successfully engaged the fish, and with force applied by the Well Stroker, the fish was retrieved to the surface.
By providing real-time information on tool performance, the operation was greatly enhanced, and it was carried out more rapidly and efficiently, in comparison to conventional fishing options.
IN THE FIELD
Initial toolsets have been placed for availability in the North Sea area, where the solution has overcome multiple complexities, such as wellbore fill, deviation and alignment of fish, to complete fishing operations that would not otherwise have been possible on e-line.
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