Offshore Operators Committee Gulf of Mexico Spotting Fluid Survey

Abstract

In the fall of 1986, the Offshore Operators Committee conducted a survey on spotting fluid use by member companies operating in the Gulf of Mexico. The purpose of the survey was to compare diesel and purpose of the survey was to compare diesel and mineral oil spotting fluids for effectiveness in freeing stuck drillpipe. The survey covered the years, 1983 - 1986. Operators were asked to specify the number of wells drilled with water base mud for each year covered by the survey (1983 - 1986) and to supply certain information on each stuck pipe event where an oil base spotting fluid was used. The results showed that the success rate for freeing stuck pipe with diesel pills was 51%, while the success rate with mineral oil pills was 33%. Introduction In recent years a substantial data base on the toxicity of drilling muds has been developed by both government and industry. These data show that water base muds containing mineral oils are normally less toxic than muds containing diesel oils at the same oil content. Whether or not this difference in toxicity has any significance from an environmental standpoint is still under debate. Nonetheless, EPA has sought to reduce 3 or eliminate the use of diesel in drilling muds and encouraged the use of less toxic mineral oils. Traditionally, diesel has had two principal uses in drilling muds: as a lubricant to reduce friction and as a "spotting" fluid to free stuck drillpipe. In this latter application, a volume or "pill" of oil base mud is pumped downhole and placed or "spotted" in the annulus opposite the point where the drillstring is stuck. After a few hours., the filter cake bonding the pipe to the formation is weakened and the pipe is pulled free. While mineral oil is considered to be a satisfactory lubricant, most operators consider diesel to be superior for freeing stuck pipe. In the fall of 1986, the Offshore Operators Committee (OOC) conducted a comprehensive survey to test this hypothesis. SURVEY APPROACH The survey covered Gulf of Mexico drilling activities for the years 1983 - 1986. Operators were asked to specify the number of wells drilled with water base mud for each year covered by the survey and to supply certain information on each stuck pipe event where an oil based spotting fluid was used. The survey asked for the date the event took place, the type of oil used in the pill, the depth where the pipe was stuck, the time interval from when sticking occurred until when the pill was spotted, whether the hole was straight or directional, and whether or not the pill was successful in freeing the pipe. Survey responses were received from 12 companies operating in the Gulf of Mexico. These 12 companies accounted for well over half the wells drilled during the survey years. DATA ANALYSIS The survey participants reported 619 spotting incidents during the survey years; however, not all of these incidents were used in this analysis. Forty five incidents took place in 1981 and 1982. These incidents plus four in the 1983–86 survey period were not used because accompanying information on the number of wells drilled with water base mud was missing. In two cases information on whether or not the pill was successful was missing. Multiple pills were used in 40 spotting incidents that occurred during the survey period. We chose to base our calculations on sticking incidents with the results categorized by the nature of the first pill, rather than on spotting incidents. For example, assume an operator had a sticking event and spotted a diesel pill. Also assume he failed to get free and spotted pill. Also assume he failed to get free and spotted a second pill. P. 517