The Economics Fishing Operations in Oil Well Drilling: Balancing Efficiency and Economics

In the oil and gas industry, fishing operations refer to the procedures used to retrieve or remove stuck or failed equipment from the wellbore. These obstructions can include stuck pipe, drill collars, parted tubulars, stuck packers, parted or stuck wireline, and other lost or failed equipment. When such conditions develop, drilling, workover, and completion operations must cease until the obstruction is removed, allowing normal operations to resume.

Obstructions in the wellbore can result from various factors, such as human error, unknown hole conditions, metal fatigue in tubulars, junk in the hole, and faulty equipment. These obstructions are generally classified into two categories: fish and junk.

A fish is a part of the drill string that separates from the upper remaining portion while the drill string is in the well. This can occur due to mechanical failure or when the lower portion of the drill string becomes stuck or disconnected from the upper portion. In such cases, an operation is initiated to free and retrieve the lower portion (or fish) from the well using a specialized, strengthened string.

On the other hand, junk refers to small, non-drillable metal items that fall or are left behind in the borehole during drilling, completion, or workover operations. These non-drillable items must be retrieved before operations can continue.

It is crucial to remove fish or junk from the well as quickly as possible. The longer these obstructions remain in the borehole, the more difficult they become to retrieve. Additionally, if the fish or junk is in an open hole section of the well, it can cause problems with borehole stability.

While fishing operations are typically less expensive than the overall drilling or workover costs, they can still have a significant economic impact on the project. If a fish or junk cannot be removed promptly, it may be necessary to sidetrack (directionally drill around the obstruction) or drill another borehole, incurring additional costs.

To ensure an economical fishing operation, a careful assessment of the problem, effective communication among all parties involved (such as geologists, reservoir engineers, and others responsible for the well), and consideration of alternative options (like open-hole sidetracking or cased-hole casing exit) are essential. Experience, good judgment, and the use of probability factors based on similar situations can also aid in determining the appropriate course of action and the time to be spent fishing.

In order to do the economic justification, the numbers of day of fishing operation can be determined by the following equation.

D = (V  + Cs)÷ (R + Cd)

V is the replacement value of the fish
Cs is the estimated cost of the sidetrack or the cost of drilling a new well
R is the cost per day of the fishing tool and services
Cd is the cost per day of the drilling rig and other support

Advances in fishing, milling, and sidetracking technologies, along with a large database of information on fishing operations, have made decision-making easier for operating companies. However, every situation is unique, and a standard checklist applicable to all scenarios would be impossible. The ultimate goal is to return to normal drilling, completion, or workover operations with minimal lost time and money.

In summary, fishing operations play a crucial role in the oil and gas industry, enabling the removal of obstructions from the wellbore. By employing effective strategies, considering economic factors, and leveraging advanced technologies, companies can successfully overcome these challenges and resume operations efficiently.


The Guide to Oilwell Fishing Operations: Tools, Techniques, and Rules of Thumb (Gulf Drilling Guides) by Joe P. DeGeare, David Haughton, Mark McGurk

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