The aim of this work was to give rig site personnel a way to calculate how long to personnel a way to calculate how long to fish for stuck pipe. The paper reports on the collection of stuck pipe data, the development of a fishing equation and a means of estimating side-tracking costs. Introduction An internal study undertaken by BP Exploration operating Company in 1988 found that stuck pipe was the largest single contributor to non-productive drilling time. The problem cost the Company more than $30 million a year between 1985 and 1988. As a result of these findings, a task force was formed with the sole aim of reducing stuck pipe related costs. One of the many issues addressed by this task force concerned the length of time that fishing should continue after becoming stuck. The aim of the work was to provide rig site personnel with a simple guide to fishing time, irrespective of the type of stuck pipe or the method of freeing attempted. Earlier research has produced equations which determine how long fishing operations can be economically justified. These were based on Gulf of Mexico wells. The work presented here investigates the economics of fishing in the North Sea. The effort was justified by an early BP task force review, which showed that the Gulf of Mexico and the North Sea have significantly different sticking problems. In the Gulf of Mexico, most stuck pipe is due to differential sticking and spotting a diesel based pill is considered to be the most successful remedy. In the North Sea, mechanical sticking is the major problem and the best remedial action is less obvious. Spotting a pill is only one of a number of possible options. Historically, the decision to carry on or abandon fishing has been made by Rig Supervisors and Drilling Superintendents based on knowledge of the incident and past experience. Invariably, some effort past experience. Invariably, some effort will be made to free the pipe. This is easily justified because there is a good chance of freeing the string quickly and the cost of a few hours rig time is usually far less than a side-track. It is equally clear that highly protracted fishing operations are uneconomical. The problem is to choose a cost-effective problem is to choose a cost-effective fishing time somewhere between these two extremes. In 1984, Keller et al of Mobil introduced the concept of Economic Fishing Time (EFT). They developed an equation to calculate the time at which the cost of fishing becomes equal to the cost of an immediate side-track, taking into account the probability of successful fishing, as follows: P x KHCEFT = DFC (1) where, EFT = Economic fishing time in days. Ps = Probability of successful fishing. KHC = Known hole costs (Value of fish +cost to redrill to original depth). DFC = Daily fishing cost. P. 507
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