整体螺旋式扶正器内螺纹接头断裂失效原因分析

The Fracture Failure Cause Analysis of Internal Thread Joint of The Integral Spiral Centralizer Song Tao1， Li Zhenkun1，Li Tie2，Fu Hui1
1. CNOOC Ener Tech-Drilling & Production Co.，Tianjin 300452 2. Pengbo Operating Company of CNOOC （China） Co. Ltd.，Tianjin 300459 Abstract：Objective Through analysis the failure behavior of the internal threaded joint of the whole spiral type centralizer in an oilfield ，then it can be very convenient to judge the failure type of internal thread joint of the whole spiral type centralizer，and to analyze the characteristics of crack generation as well as the working condition and operation of the well，thus can confirming the environmental medium factors of fracture failure，and providing support for similar well conditions to improve the use status of the overall spiral centralizer and extend the service life. Methods Based on the preliminary judgment of the macroscopic analysis of the internal threaded joint of the fractured spiral centralizer，the failure of the internal thread joint of the integral screw centralizer was systematically analyzed by means of scanning electron microscopy and metallographic analysis. Results The mechanical properties，chemical composition and metallographic structure of the integral spiral centralizer were in accordance with the requirements of 4145H in ASTM A304. The micro-morphology of the fracture surface is intergranular and there are corrosion marks on the surface of the grain. It is found that the corrosion products contain Fe， C，O，Cr，Mn，S，Na，Si，Ca，and the presence of S element can be confirmed that the presence of hydrogen sulfide in the working condition. These characteristics indicate that the internal joint cracking mechanism of the whole spiral centralizer is hydrogen stress corrosion cracking. The presence of sulfur was also confirmed by X-ray energy spectrum analysis of the corrosion products on the fracture surface，also confirming the existence of FeSx. The high temperature drilling fluid used in the drilling process is a high temperature resistant sulfuric acid brine-based mud. When the water-based mud temperature is higher than 155℃，H2S is chemically decomposed，thereby confirming the medium factor of sulfide corrosion. The daily drilling report of the well showed that the actual bottom hole temperature reached 165℃，and the phenomenon of the difficulty of back reaming and frequent squeaking of the torque confirmed the stress factor. Conclusion The fracture failure of the internal threaded joint of the whole spiral centralizer in this oilfield is mainly caused by hydrogen sulfide corrosion under the secondary H2S environment，and hydrogen stress cracking is caused by excessive local stress which is used by the whole spiral centralizer. The material used in the whole spiral centralizer is 4145H，which is a high-strength alloy structural steel. It has a higher sensitivity index to hydrogen sulfide，so it is more prone to hydrogen sulfide stress corrosion cracking. For similar well conditions，reasonable mitigation and shielding of hydrogen sulfide stress cracking will provide important theoretical support for extending the life of the drill string and drilling tools. Keywords：integral spiral centralizer；internal thread joint；the analysis of fracture failure；morphology analysis；the analysis of product composition；sulfide corrosion；stress cracking.
2019年第Байду номын сангаас期
勘探开发
整体螺旋式扶正器内螺纹接头断裂失效原因分析
宋涛1 李振坤1 李铁2 付辉1
1.中海油能源发展股份有限公司工程技术分公司 天津 300452
2. 中海石油（中国）有限公司蓬勃作业公司 天津 300459 摘要：目的 分析某油田整体螺旋式扶正器内螺纹接头失效行为，便于确定该油田整体螺旋式扶正器内螺纹断裂失效类 型、分析其裂纹产生特点并对该井工况和作业进行了分析，从而证实断裂失效的环境介质因素，对类似井况改善整体螺旋 式扶正器的使用现状，延长使用寿命，提供了支持。方法 基于断裂整体螺旋式扶正器内螺纹接头宏观分析的初步判断， 采用扫描电镜微观分析、金相组织分析等方法，对失效的整体螺旋式扶正器内螺纹接头展开了系统分析。结果 该整体螺 旋式扶正器力学性能、化学成分及金相组织均符合ASTM A304中4145H要求标准。纹断口微观形貌为沿晶，晶粒表面有腐 蚀痕迹，通过对腐蚀产物分析发现含有Fe、C、O、Cr、Mn、S、Na、Si、Ca等元素，S元素的出现，可以证实工况中含有 硫化氢，这些特征说明整体螺旋式扶正器内螺纹裂纹开裂机理为氢应力腐蚀开裂。利用X射线能谱对断口表面腐蚀产物分 析也发现硫的存在，证实了FeSx的存在。而钻井过程中所用的高温钻井液为抗高温硫酸盐水基泥浆。此种水基泥浆温度高 于155℃时化学分解出H2S，从而证实了硫化物腐蚀的介质因素。该井的钻井日报显示实际钻井时井底温度达到了165℃， 并且出现倒滑眼困难，频繁蹩扭矩的现象，证实了应力因素。结论 该油田整体螺旋式扶正器内螺纹接头断裂失效，是在 次生H2S环境下，以硫化氢腐蚀为主，由于局部应力过大，而产生的氢应力开裂；由于该整体螺旋式扶正器所用材料为 4145H，是高强度合金结构钢，对于硫化氢应力敏感指数较高，故更容易发生硫化氢应力腐蚀开裂。对于类似井况，合理 减缓和屏蔽硫化氢应力开裂，对延长钻柱及钻井工具使用寿命具有重要的理论支持。 关键词：整体螺旋式扶正器 内螺纹接头 断裂失效分析 形貌分析 产物成分分析 硫化物腐蚀 应力开裂