蒸汽吞吐热采井套管材料长时服役性能预测方法研究

Heavy oil is one of the important oil & gas resources in China which is extracted dominantly by cyclic steam stimulation process. During the normal production obvious damage occurred and resulted in lots of thermal elastic and plastic failures for casing string due to the large scale temperature alternation and axial displacement constraint. The long term service properties degradation for casing material has not been introduced into the newly developed strain based design method for thermal casing, which makes the designer unable to determine the factual plastic capacity during the long term cyclic production. This project will focus on the properties evolution and damage mechanism research of casing material with alternate temperature and axial load, based on strain-based design method under axial zero displacement constraint for cyclic steam stimulation thermal wells. Casing materials representing different service experience and damage state will be achieved through simulation treatment equipment for cyclic steam stimulation process in lab. The systematic experiments will be done to achieve the properties evolution feature from three aspects including of strength and plasticity, stable creep rate equation, and low cycle fatigue life as well. The macro and micro damage morphology and mechanisms will be observed and analyzed to assist in building the expression method and prediction models of different material properties for long term cyclic service environment.These models will be used to build casing selection method. The results will present scientific guide in determining material plastic capacity for strain-based casing design and material selection around factual thermal wells engineering in Xinjiang oil field or other area.

稠油是我国重要油气资源种类之一，主要作业工艺是循环蒸汽吞吐。由于井筒温度的大幅变化和套管柱的轴向位移受约束，套管在循环作业中产生累积损伤，造成大量热弹-塑性失效。新的基于应变的套管柱设计方法尚未引入材料的长时服役性能劣化规律，无法确定材料的塑性变形容量。本课题将围绕热采井变温变载历程对约束状态下的套管材料性能影响，开展材料长时服役性能演变规律与损伤机理研究。通过模拟热采井多轮次蒸汽吞吐作业工况，获得材料的不同服役历程与损伤状态。从套管材料强度与塑性演变规律、稳态蠕变速率方程演变规律、低周热应变疲劳寿命演变规律三个方面开展系统的试验研究，结合材料宏微观损伤形貌观察与机理分析，建立轴向零位移约束及热-力耦合交变场下套管材料长时服役性能表征方法及预测模型，并建立热采井套管选用方法。研究成果将依托新疆油田等稠油热采井工程，在掌握套管材料性能劣化规律的基础上，为套管柱应变设计与选材确定材料塑性变形容量提供科学依据。

本课题围绕热采井变温变载历程对约束状态下的套管材料性能影响，开展了不同服役历程与损伤状态。针对热采井用80SH和N80Q钢中温温区（300℃至450℃）蠕变稳态速率规律进行了试验研究。中温高应力条件下80SH和N80Q钢都存在明显蠕变行为，稳态蠕变速率随应力幅的增加呈现指数关系，80SH钢的稳态蠕变速率显着小于N80Q钢，表现出良好的抗蠕变性能。在蠕变过程中，N80Q钢在晶界处首先出现位错塞积，稳态阶段位错组态演变为网状亚晶结构；80SH钢位错亚结构由滑移位错切割强碳化物析出相演变为层错和微孪晶。80SH钢良好的蠕变抗力是由于合金元素Cr、Mo引起的固溶强化，以及多尺度M23C6、MX型析出相相互作用的结果。.基于材料的热塑性蠕变规律及现场服役工况，提出套管柱基于应变设计新方法，确定了设计应变和许用应变的计算方法及流程，制定了国家标准1项，开发了2种套管产品，在新疆油田应用8口井，服役8年期间未发现套损现象，实现了套损的有效控制，确保国家稠油开发产能建设。.从套管材料强度与塑性演变规律、稳态蠕变速率方程演变规律、低周热应变疲劳寿命演变规律三方面开展系统试验研究，结合材料宏观微观损伤形貌与模型，自主研制热-力耦合工况零位移约束工装1套，发表论文16篇，授权专利6件，培养人才7人次。