Situations, where fishing is necessary, can arise during oil and gas well drilling or workover operations.
Fishing situations occur when equipment is stuck or lost in the hole. They are quite common in oil and gas well drilling or workovers. It happens to one in five wells.
While some fishing operations are simple, some of them can be very difficult or even impossible.
When fishing is impossible or deemed too difficult, the operator can opt to either redrill a new well or to sidetrack by opening a new track in the existing hole to bypass the fish.
Here are the two commonly asked questions when an operator is in a fishing situation.
- Should we fish or not?
- How much time should we spend to recover the fish?
Many fishing jobs are difficult and require special tools and the expertise of a fishing specialist. However, even with the best tools (which may have a high daily cost) and procedures, sometimes the fishing attempt fails or takes a long time.
It is vital to know everything possible about the fish and fishing conditions before starting the job so you can ascertain the level of difficulty. The operator should consider some fishing jobs impractical from the very start. For example, drill collars accidentally cemented in or engulfed in barite are nearly impossible to recover and are not worth the cost, even if they are recovered. In these situations, you should not proceed with fishing and should begin side-tracking instead.
When it is difficult to decide what is fishable and you do not know the probability of success, it is best to estimate the cost of side-tracking and determine how long to fish.
The cost of side-tracking can be estimated easily. It takes about 5 days to set a cement plug on top of a fish and kick off the hole to bypass the fish.
You can estimate the cost of drilling a new hole to reach the original total depth if you know the:
- rate of penetration
- length of the original hole.
It is also important to recognize when it is time to stop fishing and start re-drilling. You need to determine how long to fish so that the cost of the fishing operations and lost drilling time do not exceed the cost of side-tracking.
Generally, you should stop fishing and decide to sidetrack the well when the cost of fishing has reached about half the cost of side-tracking.
The following equation calculates the number of days that should be allowed for fishing.
D = (V + CS)/(R + CD)
where:
D = Number of days to be allowed for fishing
V = Replacement value of the fish
CS = Estimated cost of side-tracking
R = Daily cost of fishing tool rental and services
CD = Daily rig operating cost.
After you calculate the maximum number of days to spend fishing, you may realize that it will take longer than the allotted time to fish. In this case, it would be better off to side-track instead of attempting to fish.
This article is written by Rick Patenaude. Rick started his oilfield career in the Powder River Basin of Wyoming in the mid-1980s. He joined Weatherford as a Fishing Tool Supervisor in 1995 and worked throughout the Rocky Mountain Region until 2003. Rick transferred to China in 2003 to support Weatherford’s operations in the Pearl River Basin and Bohai Bay until 2006. Rick was then transferred to Jakarta to support the growing well-intervention market for both national and international clients. In 2012 Rick was assigned to Balikpapan as Project Manager Fishing & Re-Entry Services for Chevron’s West Seno Extended Reach Drilling Project. Upon completion of the West Seno Project Rick returned to Jakarta and began supporting operations throughout the Asia Pacific Region including New Zealand, Australia, India, Brunei, Malaysia & Japan.
The photo above shows the fish recovered with a skirted screw-in sub after a successful wash-over operation to burn off the blades on the integral bladed stabilizer. The fish is a 12-1/4″ OD directional drilling BHA.
