Tool Joint Heat Checking While Predrilling for Auger TLP Project

Abstract

SPE and IADC Member Abstract Heat checking cracks on tool joints occurred on 57% of a 22,000' drill string while drilling two wells during the Auger TLP Project pre-drill program. The cracks formed after the tool joint was friction heated while rotating under side loads and then quenched by drilling mud. It is thought that the primary cause of the heat checking was due to abrupt doglegs at the flexjoint between the marine drilling riser and the subsea BOP stack and large doglegs in the angle building section of the well. The addition of raised metamorphic alloy hard banding to the tool joints, improved monitoring of the flex joint angle, and revised operational practices reduced the incidence of heat checked tool joints dramatically. Introduction Shell Offshore Inc. in May 1990 began pre-drilling wells for the Auger Tension Leg Platform (TLP) project in 2862' of water in the Gulf of Mexico. Ten wells were drilled to total depth and an additional ten wells were drilled and cased to surface casing depth. The wells were drilled from a semi-submersible equipped with a top drive. The total depth of eight of the wells were approximately 19,500' true vertical depth (TVD) and the other two were drilled to approximately 16,500' TVD. After drilling the fourth well of the program, split boxes in the drill pipe were noticed. A subsequent detailed inspection of the drill string revealed that 57% of the joints of the string had cracks in one or more tool joints. The 5 1/2" drill pipe drill string had only been used to drill the third and fourth wells of the drilling program. The type of cracks discovered in the drill string were thought to be caused by heat checking. Heat checking occurs when steel which has been heated by friction is quenched by either the underlying cool metal or the drilling fluid. Heating of steel above the critical temperature of 1450F allows austenite to form. Rapid cooling (quenching) of the metal transforms the austenite to a hard untempered martensite that is susceptible to crack formation. A test program to determine loads that would cause heat checking showed that the addition of a raised layer of metamorphic alloy hard banding helped prevent formation of heat checking cracks. At Auger, the 5 1/2" drill pipe tool joints had not been originally hard banded because of casing wear concerns. Wear from drilling the first two wells with 5 1/2" drill pipe reduced the tool joint outer diameter (OD). To prevent additional wear and provide protection against heat checking, the tool joints of the 5 1/2 drill string were hard banded with the metamorphic alloy hard banding material. Several potential causes of the heat checking problem were studied and changes in operational practices were implemented. These changes included 1) monitoring and adjusting rig position and riser tension to minimize the angle between the subsea BOP stack and marine drilling riser; 2) increased hole inclination survey frequency while building angle; 3) reduced build rate in angle building portion of well; 4) drill shorter intervals in an oriented mode with a mud motor; and 5) use smaller drill pipe on the bottom of the drill string to reduce tensions and thus side loads. DESCRIPTION OF HEAT CHECKING PROBLEM SEEN AT AUGER The first two wells were drilled at Auger to total depth (TD) using the rig's existing 5" drill pipe. P. 941^