酸性气田低合金钢环境致裂损伤行为研究

Based on the double pressure of safety and cost in the development of aicid gas field, the economical and reliable low alloy steel has wide application space. One of the key factors that determine the safe use of the environment is the crack damage behavior. As the basis of the theory of petroleum engineering, the theory of fracture and damage mechanics and the theory of corrosion electrochemistry, the corrosion test device of high temperature and high pressure constant load, three point bending stress and the test apparatus of hydrogen permeation was improved, and the relationship between the hydrogen permeation and the strength as well as the plastic damage behavior of low alloy steel was studied with low alloy steel C110 and P110 as the research object in the H2S/CO2 acid gas field in this paper. The crack propagation and damage law of low alloy steel H2S/CO2 in acidic gas field were discussed from three aspects of hydrogen permeation mechanism, hydrogen atom interaction with dislocation and crack nucleation. A calculation model for the strength, toughness and hydrogen permeation parameters of low alloy steel in acid gas field was established. The change rules of the stress intensity factor and strain energy of low alloy steel in acid gas field were shown. The effects of acidic gases on interfacial adsorption, cathode and anode electrochemical reaction and hydrogen permeation mechanism were studied. The evaluation method and the criterion of strain energy criterion for environmental cracking of low alloy steel in acidic environment were put forward, which could provide theoretical basis for the evaluation method of H2S/CO2 environmental fracturing in acid gas field.

基于酸性气田开发安全和单井成本双重压力，经济可靠、性能稳定的低合金钢具有广泛应用空间，环境致裂损伤行为是决定其能否安全使用的关键因素之一。本研究以石油工程理论、管柱断裂与损伤力学、腐蚀电化学理论为依据，以H2S/CO2酸性气田环境中低合金钢C110、P110为研究对象。改进完善高温高压恒载荷、三点弯曲应力腐蚀实验装置和氢渗透测试装置，研究氢渗透与低合金钢强度、塑性损伤行为之间的作用关系。分别从氢渗透机制、氢原子与位错的交互作用以及裂纹形核扩展三个方面研究低合金钢在酸性气田H2S/CO2下的裂纹扩展和损伤规律；建立酸性气田低合金钢强度、韧性与氢渗透参数之间的计算模型；掲示酸性气田低合金钢应力强度因子、应变能的变化规律。探讨酸性气体对界面吸附、阴阳极电化学反应和氢渗透作用机理；提出酸性环境中低合金钢环境致裂适用性评价方法及应变能判据准则；为酸性气田H2S/CO2 环境致裂评价方法提供理论依据。

在酸性气田开采过程中，高温、高压、高矿化度地层水以及高含H2S、CO2 酸性腐蚀气体环境，使得石油管服役条件更加复杂恶劣，导致因腐蚀而诱发的失效问题非常严重。对于高温高压酸性油气井筒而言，油井管处于复杂的受力状态，存在不同形式的断裂风险和隐患。在酸性油气田开采过程中，油套管材的环境致裂是最危险的失效形式。但是基于酸性气田开发中安全和单井成本的双重考量指标，经济可靠、性能稳定的低合金钢具有一定的应用前景。环境致裂损伤行为研究是决定低合金钢能否在酸性气田环境中能否安全使用的关键。本研究以酸性气田环境中低合金钢C110、P110为研究对象，通过设计完成了圆形夹具和板型夹具的恒载荷应力加载装置，改进完善了高温高压恒载荷、三点弯曲应力腐蚀实验装置(70MPa、200℃动态循环多相流高温高压釜、恒载荷应力腐蚀实验装置)和氢渗透测试装置，研究了氢渗透与低合金钢强度、塑性损伤行为之间的作用关系。分别从氢渗透机制、氢原子与位错的交互作用以及裂纹形核扩展三个方面研究了低合金钢在酸性气田H2S/CO2下的裂纹扩展和损伤规律；建立了酸性气田低合金钢强度、韧性与氢渗透参数之间的计算模型；掲示了酸性气田低合金钢应力强度因子、应变能的变化规律；通过研究酸性环境中低合金钢在静载荷、动载荷和缺口敏感三种不同条件下油井管应力强度因子KI，得出了酸性环境中低合金钢环境致裂适用性评价方法及三种不同油井管腐蚀速率下（油井管腐蚀速率v≤0.076mm/a、油井管腐蚀速率0.076mm/a﹤v≤0.1mm/a、油井管腐蚀速率0.076mm/a﹤v≤0.1mm/a）的应变能判据准则，建立了系统完善、稳定可靠的油井管环境敏感开裂适用性评价方法，运用阳极溶解理论和氢致脆化理论解释油井管环境开裂机制，为环境敏感开裂研究提供新的思路和理论基础，为酸性气田H2S/CO2 环境致裂评价方法提供了理论依据。