PROTECTIVE PROPERTIES OF CRUDE OIL ON CO2 CORROSION IN OIL AND GAS FIELDS

摘要

The corrosion behavior of API-X65, 1Cr-X65, 16Mn, 3Cr-L80 in oil/water media were investigated by using horizontal/vertical autoclave in this paper. The morphology, composition and microstructure of corrosion scales were analyzed by means of SEM 、EDS 、XRD. After exposed on the oil/ water separate media for 240h, the coupons were corroded severely in the water while slightly in oil. Crude oil may absorb to the surface of coupons to form a protective layer, therefore decrease the corrosion rate considerably. A typical FeCO3 crystalline was formed on surfaces of API-X65 、16Mn exposed on water phase while some Cr-containing compounds were formed on the surface of 3Cr-L80. These Cr-containing compounds had poor adhesion to substrate and cracked easily after dehydration. The corrosion is very slight for all the three steels in the oil phase and a polished surface maintain on the surface of the coupon. The boundary of the scale between oil and water phase is obvious. The simulative testing of API-X65, 16Mn, 1Cr-X65 under the alternate oil/water mixture indicated that the corrosion rate of the materials increased with the increase of water cut, fluid velocity and partial pressure of CO2, but decrease with the growth of temperature. When the media contain 100% water or 15% oil, the corrosion of the testing materials were severely. When the media contain 30% oil, the corrosion was slight with a polishing surface. Crude oil changed the aqueous chemistry, affecting the corrosion rate and protectiveness of the corrosion product layer formed on the steel.