全尺寸石油管柱高温高压应力腐蚀/开裂研究及未来发展方向

Stress Corrosion and Cracking of Full-scale Tubing String under High Temperature High Pressure

采用自主研制的全尺寸石油管高温高压应力腐蚀系统成功模拟了高温高压气井油管柱的腐蚀过程,克服了以往传统小试样高温高压腐蚀方法研究油气井管柱腐蚀的缺点。以高温高压气井常用的全尺寸超级13Cr油管(88.9 mm×7.34 mm)为研究对象,模拟酸化压裂过程中残酸返排阶段油管在120℃残酸介质中,在70 MPa内压和78.6%实际屈服强度轴向拉力载荷下的腐蚀行为及应力腐蚀开裂演化过程和机理。研究结果表明,全尺寸超级13Cr油管在残酸—高温—内压—轴向拉力共同作用下发生了严重点蚀和应力腐蚀开裂。裂纹起源于油管内壁的腐蚀坑,开裂方式为沿晶开裂,开裂过程为:随着腐蚀坑长大,在腐蚀坑部位形成"X"型裂纹,最终导致开裂。最后从三个方面系统阐述了全尺寸石油管高温高压应力腐蚀研究的未来发展方向。

A self-made device called＂full-scale tubular goods corrosion test system＂was used to simulate downhole corrosion of high pressure high temperature（ HPHT） gas well,which successfully overcame the disadvantages of conventional small-coupon HPHT test in autoclave. A super 13 Cr tubing（ 88. 9 mm × 7. 34 mm） was tested in spent acid at 120℃ with 70 MPa inner pressure and 78. 6% actual yield strength to simulate the HPHT gas well acidizing process. The results showed that severe pitting corrosion and stress corrosion cracking were occurred under combined action of spent acid,high temperature,inner pressure,and axial tensile stress. Crack initiated from corrosion pits of tubing inner surface,which propagated in intergranular mode,the mechanism is that the corrosion pits developed to X-shaped crack with pit growth,and finally resulted in cracking. Moreover,the future directions of full-scale tubular goods corrosion test system were discussed in three aspects.