Reaching New Depths In Fishing Operations

As operators strive to bring new wells onto production as quickly as possible, the loss of drilling and completion tools downhole is not good news. When hardware drops to the bottom of the hole or becomes wedged in the well, operators are often left no choice but to run a fishing operation to retrieve it.

Fishing operations are unplanned interventions that add cost and time to a well completion and require bringing in myriad specialty retrieval equipment—junk baskets, milling and cutting tools, and external or internal catch tools—to retrieve the dropped equipment and bring it back to surface. While estimates vary regarding the financial impact of fishing to the industry as a whole, an oft-cited statistic indicates that fishing operations may account for 25% of drilling costs worldwide.

While such operations have been conducted since the earliest days of oilfield drilling, the fishing jobs of today are hampered by the greater complexity and depth of newer oil and gas wells. Onshore, advances in horizontal drilling have created laterals reaching thousands of meters away from the vertical section of a well. Deploying fishing tools into these long laterals is often hindered by rapid changes in trajectory or the risk of getting hung up on ledges or well debris that was not removed during hole cleaning.

The costs and complexity of fishing operations are often compounded in deepwater wells, where the tool to be fished out of the wellbore (typically referred to as the “fish”) may be at the bottom of a well that extends thousands of meters below the seafloor. Retrieval requires hiring a vessel to perform the fishing job, an expense that may add several hundred thousands of dollars to the well’s costs.

Well abandonment is often not an option for a deepwater well as the well’s owner may have already invested several millions of dollars in drilling and completions costs. A safe, speedy and minimal-cost fishing operation is often the only course of action to save the well and bring it onto production.

For operators, this requires partnering with a service provider with specialized expertise in well interventions and fishing operations. Such expertise must include a wide range of fishing tools and systems, including packer milling and retrieving, internal and external cutting, hole enlargement and washover equipment for fishing jobs in cased hole, and openhole and through-tubing applications. It also must include the field experience to deploy these tools effectively and make necessary adjustments as needed to remove obstructions from deepwater wells as safely and efficiently as possible with minimal trips downhole.

Deepest fishing job in GoM well

While conducting a formation evaluation operation in a deepwater Gulf of Mexico (GoM) well, an operator lost a wireline coring tool 457 m (1,500 ft) off bottom in an 8¹/₂-in. hole section. The tool was 19 m (62 ft) long with a 6¹/₂-in. outer diameter and a fishing neck of 3²¹/₃₂-in. to engage the fish for recovery. The operator needed to continue formation evaluation and recover the coring tool with minimum operational time and risk and reached out to Baker Hughes for a solution.

After analyzing the situation with the operator, the service provider’s fishing team suggested running a 5³/₄-in. Series 150 releasing and circulating overshot tool. The Series 150 overshot tool is designed to externally engage, pack off and pull a fish. The basic tool comprises a rugged construction and three outside parts—a top sub, bowl and guide. It can be dressed with two different sets of internal parts, depending on the relative size of the fish.

If the fish is near the maximum size for the overshot, a spiral grapple and control and Type A packer are used. If the fish’s diameter is instead considerably smaller than the maximum size, as was the case for this wireline coring tool fishing job, then an 8-in. oversized guide equipped with a 3²¹/₃₂-in. basket grapple and a mill control packer is deployed. This configuration was deemed to provide the best attempt to retrieve the stuck tool safely and efficiently.

The fish was initially tagged at 9,773 m (32,066 ft) with 10,000 lb set-down weight but then fell to the bottom of the hole. The fish was tagged again at a depth of 10 km (33,789 ft), nearly 6.5 miles below the seafloor, which marked the deepest fishing operation ever attempted to date. Pick-up and slack-off weights at this depth were 1.06 MMlb and 1.004 MMlb, respectively. With such a small weight differentiation and the extreme depth of the well, this was a not a clear indicator that the fish was engaged. Team members used their knowledge and expertise to use other indicators such as pressure to show that the fish was inside the overshot.

Two attempts to secure the fish were made both with and without pumps circulating. The pressure would increase to 300 psi when over the fish but would fall off when the string was picked up, indicating that the wireline tool had not been secured.

On the third attempt, with the pumps working at 10 strokes per minute and applying 13,000 lb to the fish, the pressure increased when the overshot went over the fish and held when the pumps were shut off. The overshot assembly was picked up 9 m (30 ft), confirming that the fish was caught. The pressure continued to hold and a slug was pumped, enabling the fish to be tripped out of the hole without further incident.

The wireline coring tool was recovered in a single trip that took 27 hours to make one-way. The total roundtrip took only 54 hours as opposed to the hundred or more hours that would have been required for multiple trips, saving multiple days of rig time at the rate of $550,000/d.

Because this operation eliminated additional downhole trips, the risk of wellbore damage also was eliminated. The operator was then able to continue formation evaluation without further interruption.