RIASSUNTO
Abstract
The stickiness factor is an empirically derived number strongly related to the chances of freeing stuck pipe in a well. The number is defined by the following equation:
Stickiness Factor =
.....................................(1)
where: is the maximum angle in the open hole (degrees); OH is the amount of open hole (feet); MW is the mud weight (lb/gal); FL is the API-fluid loss (cc/30 min); and BHA is the bottom-hole-assembly length (feet).
The relationship between the stickiness factor and the historic chances of freeing stuck pipe is illustrated by the chance curve of Figure 1. Basically, the stickiness factor should be kept below 2.5 wherever practical. Since stuck pipe costs are largely dependent on the ability to free stuck pipe and avoid sidetracking a well, it follows that reduced stickiness factors should result in reduced stuck pipe costs. The stickiness factor is commonly lowered by reducing the API-fluid loss of the mud, reducing the bottom-hole-assembly length, or setting casing.
The stickiness factor is based on a study of Gulf of Mexico wells drilled by Exxon Company, USA. Therefore, it will not necessarily apply well in other areas. The factor not predict when pipe will stick, but simply predicts the chance of freeing pipe that has already been stuck.
The stickiness factor will also help evaluate various spotting fluids and fishing techniques since it indicates the relative difficulty (chance of success) of a soaking or fishing job.
Finally, a reduced stickiness factor should reduce the chances of sticking pipe.
Introduction
Stuck pipe is a very costly problem in drilling. It is especially costly in the Gulf of Mexico where stuck pipe alone can increase development drilling costs in a particular field by as much as 30%. Most of these offshore wells have drift angles of 20 to 60 degrees. Many go into abnormal pressure requiring weighted drilling muds. Experience has led many to believe that angle and mud weight are two of the strongest factors causing pipe to stick and to remain stuck. Even so, many stuck pipe occurrences have not been well understood. It is the need for further understanding and the potential cost savings involved that a comprehensive study of stuck pipe began.
A statistical analysis of field data is one method of studying stuck pipe. The most desirable result of such an analysis would be a means of predicting when pipe will stick. However, to analyze predicting when pipe will stick. However, to analyze the chances of sticking pipe, one would have to include data from times when pipe wasn't stuck as well as data from stuck pipe occurrences. In other words, data would have to be included from every well for every day that rigs were working in open hole. It is not difficult to see how the volume of data for this type of analysis would be overwhelming.
A more practical result would be a means of predicting when stuck pipe will be freed. Such a predicting when stuck pipe will be freed. Such a result would be valuable because the average ""not-freed"" occurrence costs about ten times the average ""freed"" occurrence. Thus, overall stuck pipe costs will be reduced if the chances of freeing stuck pipe are improved.
So data were gathered and statistically analyzed to uncover correlations with respect to success in freeing stuck pipe. The data came from 113 occurrences of open-hole stuck pipe from a three-year period. All of the occurrences were from Gulf of period. All of the occurrences were from Gulf of Mexico wells drilled by Exxon Company, USA. Nearly all of the wells were drilled with seawater mud systems containing no oils. Among the information recorded from each occurrence were fourteen primary ""parameters"" (Table 1) that were suspected of having some relationship to the chances of freeing stuck pipe. pipe. P. 225