Economic and Statistical Analysis of Time Limitations for Spotting Fluids and Fishing Operations
Authors: Keller P.S. , Brinkmann P.E. , Taneja P.K. 
Published: October 2008

This paper reviews the statistics of "Spotting Fluids" to free stuck drill pipe as well as the economics and statistics of drill string fishing operations. Data were taken from Mobil Oil Exploration and Producing Southeast Inc.'s (MOEPSI) records from 1970-1981. Only' those events-which occur after a drill string becomes stuck are discussed. The data collected were categorized as Directional Wells and Straight Wells. Bar diagrams are presented to show the Success Ratio vs. Soaking Time for each of the two categories. An analysis was made to identify the elapsed time limit to place the spotting fluid for maximum probability of success. Also determined was the statistical minimum soaking time and the maximum soaking time. For determining the time, limit for fishing operations, the following criteria were used:The Risked "Economic Breakeven Analysis" concept was developed based on the work of Harrison.Statistical Probability of Success based on MOEPSI's records from 1970-1981.

INTRODUCTION

Stuck drill pipe is a costly and time consuming problem. In recent years hundreds of days and' millions of dollars have been spent soaking and/or fishing stuck pipe. Mobil Oil Exploration and Producing Southeast Inc.'s (MOEPSI) experience from 1970-1981 provided data as the basis for our results and recommended future procedures. In that 12-year period, 58 spots were pumped in place and 63 fishing jobs were implemented. Not all incidents of stuck drill pipe and fishing operations could be used in this analysis due to insufficient data or extraordinary circumstances in several cases. In this study, 91% or 53 spots, along with 70% or 44 fishing jobs were analyzed. The data gathered were divided into straight and directional wells.

The purpose of this study was to identify the time constraints associated with successful soaking and fishing operations. These time constraints, implemented, can reduce economic losses resulting from continued soaking and fishing operations. The relationships and specific time limitations developed can be directly applied to Gulf of Mexico operations. This method of data and economic analysis can be used to supplement the existing "RULES OF THUMB" practices in any area while making soaking and fishing decisions.

SOAKING OPERATIONS

Two stages of soaking operations were examined: first, the time before pumping the spot, and second, the total in-place soaking time. Each operation time is examined by plotting the probability of soaking success as a function of time. Success probabilities are presented in two ways. First, success ratios for discrete time intervals are plotted as a function of time. Second, the remaining probability of future success is plotted as a function of time, condo plot, probability of future success, should be considered the more useful probability graph because it represents the actual remaining probability of freeing the stuck pipe at any given time.

Straight wells had a higher success ratio than directional wells in soaking stuck pipe, however the time limitations were found to be identical regardless of the well type. Figures 2 and 5 show the spot should be pumped within 16 hours of sticking the drill string.