【摘要】：在完井過(guò)程中油套管長(zhǎng)期處于具有腐蝕性的完井液中,服役條件惡劣同時(shí)連續(xù)油管還受到彎曲應(yīng)力、正應(yīng)力、扭矩等交變應(yīng)力作用,在腐蝕和交變應(yīng)力聯(lián)合作用下,使油管容易發(fā)生應(yīng)力腐蝕開(kāi)裂,造成油管突然斷裂,對(duì)油田生產(chǎn)造成巨大損失,甚至造成人員傷亡。因此,深入系統(tǒng)的研究油套管在完井液中腐蝕及應(yīng)力腐蝕的腐蝕情況,探明腐蝕機(jī)理以及存在腐蝕凹坑的油套管斷裂機(jī)理、斷裂臨界應(yīng)力及裂紋萌生和擴(kuò)展規(guī)律就尤為重要。本文選用P110、13Cr兩種常用油套管材質(zhì)在完井液中進(jìn)行靜態(tài)電化學(xué)分析,考慮溫度對(duì)其的影響。電化學(xué)極化曲線均表現(xiàn)出鈍化特性,表現(xiàn)出良好的耐腐蝕性。隨著溫度的升高材料抗腐蝕性下降,在70℃以上,耐腐蝕性降低速率變慢,腐蝕速率趨于穩(wěn)定。腐蝕以局部腐蝕為主,但未出現(xiàn)全面腐蝕,對(duì)比兩種材質(zhì)表明13Cr具有良好的耐腐蝕性能。在應(yīng)力存在條件下,13Cr鋼在甲酸鹽和氯酸鹽完井液中腐蝕規(guī)律類似,隨應(yīng)力的增加,13Cr鋼鈍化電流密度逐漸增加,高應(yīng)力時(shí)增幅更為明顯,耐蝕性下降。在甲酸鹽完井液中,隨應(yīng)力增大,P110鋼耐蝕性下降。與甲酸鹽完井液不同的是,在氯酸鹽完井液中,由于其中含有C1-,隨應(yīng)力增加,P110鋼腐蝕電位下降,說(shuō)明腐蝕傾向降低。與無(wú)應(yīng)力條件相比,一旦施加應(yīng)力,P110鋼鈍化電流密度急劇增加。通過(guò)使用失重法測(cè)得壓力、溫度、完井液對(duì)兩種油套管材質(zhì)腐蝕速率的影響,在.各溫度、壓力條件下,13Cr的耐蝕性均高于P110。隨溫度與壓力升高,13Cr和P110鋼在氯酸鹽完井液中鈍化穩(wěn)定性下降,6MPa時(shí)腐蝕最為嚴(yán)重,在甲酸鹽完井液中則存在臨界值,3MPa、90℃時(shí)腐蝕最嚴(yán)重。13Cr和P110鋼在氯酸鹽完井液中發(fā)生點(diǎn)蝕,在甲酸鹽完井液中則以均勻腐蝕形式發(fā)生。使用掃描電鏡觀察斷口形貌,13Cr和P110鋼的應(yīng)力腐蝕破裂為典型的脆性斷裂特征。對(duì)油套管應(yīng)用擴(kuò)展有限元法建模,分析表明在油套管出現(xiàn)三角形缺陷比圓錐形缺陷更具危險(xiǎn)性。分析表明斷裂臨界應(yīng)力隨著缺口深度逐漸降低,在為壁厚一半時(shí)最小。隨著裂紋弧長(zhǎng)的增大而減小,裂紋尖角為30。時(shí)臨界應(yīng)力值最小。P110與13Cr材質(zhì)橫向裂紋比縱向裂紋對(duì)拉力敏感。而在內(nèi)壓或外壓作用下,縱向裂紋比橫向裂紋對(duì)內(nèi)壓載荷敏感。同時(shí)在內(nèi)外壓與拉應(yīng)力同時(shí)作用下,使得裂紋擴(kuò)展臨界拉應(yīng)力有所降低。結(jié)合掃描電鏡觀察表明,試件在最終斷裂時(shí)端口無(wú)頸縮現(xiàn)象,端口表現(xiàn)為瞬間斷裂,端口平整而且裂紋擴(kuò)展方向與拉伸正應(yīng)力方向垂直,微觀斷口形貌表現(xiàn)為解理斷裂特征。
[Abstract]:During completion, the casing is in the corrosive completion fluid for a long time, and the service conditions are bad and the continuous tubing is also subjected to alternating stresses such as bending stress, normal stress, torque, etc. Under the combined action of corrosion and alternating stress, The tubing is prone to stress corrosion cracking, which leads to the sudden fracture of the tubing, which results in great loss of oil production and even casualties. Therefore, it is very important to study the corrosion and stress corrosion of oil casing in completion fluid, to find out the corrosion mechanism and the fracture mechanism of oil casing with corrosion pit, the critical stress of fracture and the law of crack initiation and propagation. In this paper, two kinds of commonly used oil casing materials, P110 and 13Cr, are used for static electrochemical analysis in completion fluid, and the effect of temperature on them is considered. The electrochemical polarization curves showed passivation characteristics and good corrosion resistance. With the increase of temperature, the corrosion resistance of the material decreases, and above 70 鈩，

本文編號(hào)：2258060