深井含硫工况C110套管环境开裂及表面防护技术

Environment Cracking and Surface Protection of C110 Casing in Sour and Deep Well

深井地质复杂、井眼轨迹变化大且面临高温高压含硫等苛刻工况,套管面临磨损、腐蚀损伤、断裂失效等各类风险,针对套管C110服役于含硫腐蚀环境且承受高水平拉应力时频繁发生环境敏感断裂的问题,采用慢应变速率拉伸实验(SSRT)法,研究了表面电镀Ni-W合金的套管C110在某气田模拟地层水中的环境开裂行为,分析研究表面电镀Ni-W合金对套管C110抵抗环境敏感开裂的防护效果。结果表明,套管C110在该模拟地层水中环境开裂敏感性较高,即使腐蚀速率较低仍存在环境开裂风险,且在慢应变速率拉应力作用下呈现典型脆性断裂特征;表面电镀Ni-W合金后套管C110的抗拉强度和屈服强度分别提高2.3%和6.3%;当表面电镀Ni-W合金并经过热处理后,套管C110在模拟地层水中的抗拉强度、屈服强度、断后延伸率和应变能均明显提高、环境开裂敏感性降低,断裂方式转变为韧-脆混合型断裂,说明在套管C110表面电镀Ni-W合金并进行热处理的方式,能够有效抑制套管C110发生腐蚀、开裂及破坏的风险,显著提升其抵抗环境开裂的能力及其在深井复杂含硫工况中的适用性。

The casing served in deep and ultra-deep wells with complex geological characteristics,well traj ectory and high temperature,high pressure and containing H2 S,bears severe wear,corrosion,fracture and other failure risk,frequent environment sensitive cracking occurs to C110 casing when in corrosive environment and high level tensile stress.The slow strain rate test(SSRT)was used to study the environmental cracking behavior of C110 casing plated with Ni-W alloy in the simulated gas field formation water,and the protective effects of Ni-W alloy coating on C110 casing against environment sensitive cracking.The results show that the C110 casing has high sensitivity of SCC in the simulated formation water,risk of environmental cracking exists even if the corrosion rate is low,and it is characteristic of brittle fracture under the action of slow strain rate tensile test.The tensile strength and yield strength of C110 casing after Ni-W alloy surface were increased by 2.3%and 6.3%;after Ni-W alloy coating were heated,the tensile strength,yield strength,elongation and strain energy of C110 casing in simulated formation water increased significantly,the SCC sensitivity is reduced,and the fracture mode is changed into ductile brittle mixed fracture.The phenomena indicates that the Ni-W alloy coating of C110 casing and heat treatment can effectively reduce the risk of corrosion,cracking and damage of C110 casing,significantly improve its ability to resist environmental cracking and applicability in deep and ultra-deep wells.