A Dynamic Systems Analysis of the "Rocket-Type" Launching of a Well-Casing Tubing String

Abstract

ABSTRACT A dynamic systems analysis has been made of the problem of the "rocket-type" launching of a well-casing, tubing string from a well at a hole depth of 3300 ft. The objective of this analysis has been to assess whether the observed "rocket-type" launching (15+ feet into the air) of the tubing string could have been caused by nozzle-breakthrough or tubing failure at the SRC No. 1 in Eddy County, New Mexico. The analysis considers tubing weight, fluid buoyancy, external fluid drag and fluid thrust forces on the tubing string. The tubing string and the fluid columns in the moving string and the annular region external to the tubing string are considered as a coupled dynamic system. Here the condition for motion of the tubing string is included using a one-sided inequality constraint for the resultant force on it. The dynamic system analysis has been implemented in a FORTRAN IV analytical/computer program called TUBERKET. TUBERKET allows the calculation and plotting of the four system state variables—distance traveled by and velocity of the tubing string, liquid heights in tubing string and in the annular region exterior to the tubing string (xT,vT,hT,hA, respectively)—as functions of time. Several situations of interest are considered relevant the dynamic behavior of and hence implied failure mode for the tubing string. Summary plots show typical dynamic behavior as a function of internal shut-in pressure and tubing nozzle diameter. These results indicate that for a specified shut-in pressure of 1200 psig, failure occurred in the tubing per se (at a depth of 1500 to 3300 ft) as opposed to breakthrough at the bottom nozzle opening in order to provide the "rocket-type" launching behavior of the tubing string which was observed.