Corrosion and Stress-Corrosion Cracking of Aluminum Alloy Drillpipe in a Water-Based, Low-Solids, Nondispersed Drilling Mud

Abstract

Corrosion and stress-corrosion cracking (SCC) tests were performed on aluminum drillpipe Alloy 2014-T6 in a waterbased, low-solids, nondispersed (LSND) drilling mud. Variables examined included chloride concentration, temperature, state of aeration, and effects of galvanic coupling to tool-joint steel. Electrochemical corrosion test results suggested that the aluminum alloy has adequate corrosion resistance to at least 71°C [160 0 P], even when it is galvanically coupled to steel in aerated muds. However, SCC susceptibility of the alloy in aerated muds was clearly demonstrated by slow-strain-rate and rising-stress-intensity/SCC tests. SCC did not occur in deaerated muds. We concluded that oxygen scavenging and monitoring are important to the successful performance of aluminum alloy drillstrings in chloride-containing, water-based, LSND drilling muds. These conclusions were confirmed by excellent field performance. IntroductionA highly deviated well (Fig, I) was recently drilled from a fixed offshore platform. The well was kicked off at 427 m [1,400 ft], and angle was built at a rate of 1.5°/30 m [1.5°1100 ft] to an inclination of 58° from vertical at 1615 m [5,300 ft] measured depth (MD) and 1416 m [4,846 ft] true vertical depth (TVD). The inclination angle was held at 58° to 1640 m [5,380 ft] MD and 1429 m [4,688 ft] TVD, where 340-mm [13ra-in.] casing was set. Drilling continued below the 340-mm [l3ra-in.] casing shoe, holding the inclination angle between 57 and 60° to 2830 m [9,285 ft] MD and 2054 m [6,739 ft] TVD, where 245-mm [9%-in.] casing was set. As will be explained later, continued drilling of the well required that sections of the steel drillstring be replaced with aluminum drillpipe. Thus, at the 245-mm [9%-in.] casing point, approximately 1372 m [4,500 ft] of 127-mm [5-in.] aluminum drillpipe was substituted for the steel pipe used earlier. The aluminum pipe was positioned immediately above the heavyweight drillpipe of the bottornhole assembly (BHA). The remainder of the drillstring above the aluminum drillpipe to surface was 127-mm [5-in.] steel drillpipe. Drilling continued below the 245-mm [9%-in.] casing shoe with the combined aluminum/steel drillstring, with the inclination angle held at about 59° to 3155 m [10,351 ft] MD and 2206 m [7,236 ft] TVD. At this point, an additional 457 m [1,500 ft] of steel drillpipe was removed from the drillstring and replaced with 127mm [5-in.] aluminum drillpipe in the same manner as described earlier. Drilling then continued at an inclination angle between 58 and 64° to the final total depth (TD) of 4007 m [13,145 ft] MD and 2635 m [8,645 ft] TVD. The total departure at this final TD was 2642 m [8,667 ft] from the surface location. The aluminum pipe used in this project was fitted with intemalflush, steel tool joints. 1 Approximately 250 joints (2286 m [7,500 ft]) of the aluminum drillpipe were obtained on a rental basis. Of these, 191 joints were new and 59 joints were used but in premium condition. The seamless drillpipe was specified as Alloy 2014-T6, with ...

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Revealing the role of Ru in improving corrosion resistance of titanium alloys in HCl solution

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