WEAR AND CO2 CORROSION OF STEEL COUPLINGS AND TUBING IN HEAVY OIL SCREW-PUMP WELLS

A prototype apparatus was used to investigate the effect of the conjoi nt action of CO2 corrosion and rotary sliding wear on steel couplings and tubing used in heavy oil screw-pump wells. The apparatus is versat ile in design to simulate the oil-well conditions such as temperature, rotary speed, and the side forces exerted by the couplings on the tub ing. Oil-well gases can also be passed through the system, and the app aratus can be converted to a three-electrode corrosion cell for conduc ting electrochemical studies. All tests were carried out in a produced heavy oil and formation water mixture. A comparison of the performanc e of various types of commercially available steel couplings and tubin g grades through material loss measurements is presented. The coupling s tested were made of plain carbon steel, and 'hard metal' coated stee l. The steel tubing grades L-80, N-80, and P-110 as well as plain carb on steel were among the tubing materials tested. It was found that the martensitic tubing suffered the least thickness loss but caused the m ost damage to the couplings. Also, 'hard metal' coated couplings yield ed the highest tubing thickness loss. The results are attributed to th e microstructures of the Various steels as well as their hardness valu es. The morphologies of the different materials surfaces were characte rized using scanning electron microscopy (SEM) following testing. (C) 1997 Elsevier Science S.A.