The development of deep-water gas reservoirs is one of the necessary ways to ensure China’s energy warning line and build an energy powerhouse. However, the downhole pipes of deep-water high CO2 gas wells have been in service for a long time in high temperature, high pressure, and strong corrosive environments, which are prone to corrosion failure, leading to a decline in pipe strength, affecting the accuracy of predicting the critical value of annular pressure, and increasing the difficulty of controlling annular pressure. To this end, a self-developed high-temperature and high-pressure kettle corrosion experimental device was used to study the corrosion law of downhole pipe columns in deep water high CO2 gas wells. The attenuation effects of uniform corrosion and pitting corrosion on the strength of the pipe columns were considered, and a residual strength calculation model for the pipe columns was established. A calculation method for the critical value of annular pressure in deep water wells considering different types of corrosion was proposed. The research results indicate that the initial value of the critical value of annular pressure under uniform corrosion is large, but it decreases significantly with age, and the maximum ultimate pressure decreases from 51.88 MPa to 42.40 MPa. The initial value of the critical value of annular pressure under pitting corrosion is small, and the decrease in magnitude with the annual limit is small. The maximum limit pressure value decreases from 22.30 MPa to 21.55 MPa. Considering that the critical value of annular belt pressure under uniform corrosion is mainly affected by the internal pressure strength of the technical casing in the early stage of service, and with the progress of corrosion, it is mainly affected by the extrusion resistance of the tubing in the late stage of service. Considering the critical value of annular belt pressure under pitting corrosion, it is mainly affected by the anti-extrusion strength of the tubing during the whole service period. The research results can provide a reference for the control of annular pressure in deep-water high CO2 gas wells.
ZHANG Zhi, XU Mao-yang, DENG Hao-yun, HOU Duo.
Annular Pressure Control Method for Deep-water Gas Wells under High CO2 Corrosive Environment[J].
Science Technology and Engineering, 2026, 26(8): 3550-3559 DOI:10.12404/j.issn.1671-1815.2500956
准确计算环空带压临界值是环空带压管控的关键,中外目前针对环空带压临界值制定了较多标准,如美国石油学会制定的Annular Casing Pressure Management for Offshore Wells(API RP 90-1)[14]、国际标准组织制定的Well Integrity-Part 2: Well Integrity for the Operational Phase(ISO/TS 16530-2)[15]和中国海洋石油集团有限公司制定的《海上油气井完整性要求》(Q/HS 14031)[16]。在现有标准下,中外学者对环空带压临界值进行了修正。张智等[17]将出砂冲蚀和CO2、O2腐蚀的协同作用联系起来,在已有标准基础上建立环空带压临界值计算模型。张阳杰等[18]提出自回归差分移动平均-长短期记忆模型,该模型针对数据集训练预测实例井的环空带压值,可为提高环空带压值的预测精度。张智等[19]考虑CO2腐蚀对储气库井管柱的影响,建立管柱均匀腐蚀预测模型和剩余强度计算模型,在此基础上建立A环空带压临界控制图版。张智等[20]结合管柱弹性力学、流体体积变化特点、气体状态方程等,建立了储气库井环空压力预测方法。周琛洋[21]考虑钻杆对套管的磨损以及CO2对管柱的腐蚀,建立了深水井合理环空带压范围计算模型。马英文等[22]考虑均匀腐蚀和高温引起的管柱强度衰减,建立了适用于渤海凝析气田的环空带压临界值计算。刘书杰等[23]根据深水井特殊情况,综合考虑高温、腐蚀、产量以及地层压力衰减,建立深水气井环空带压临界值计算方法。王汉等[24]在已有标准基础上计算各环空最大允许带压值,从而得到高温高压气井的临界产量。何汉平[25]通过考虑油套管自身强度、腐蚀等多种因素,建立油气井环空允许带压范围计算模型,包括最大和最小环空带压临界值。然而,前人对环空带压临界值的研究大多聚集于均匀腐蚀,忽略了点蚀对环空带压的影响,致使环空带压临界值计算不准确。因此需在现阶段研究的基础上,考虑点蚀对管柱强度的影响,形成较为全面的深水高含CO2气井环空带压临界值计算方法。
环空带压临界值由组成环空的井筒屏障单元承压能力决定,但现阶段国际和国内行业标准在计算该承压能力时通常忽略了腐蚀对承压能力的影响。一旦油套管柱发生腐蚀,强度将随服役时间增长而降低,但由于均匀腐蚀和点蚀情况下强度衰减速率不同,在研究环空带压临界值时有必要考虑不同腐蚀类型下强度随服役时间变化的情况。根据Annular Casing Pressure Management for Offshore Wells(API RP 90-1)[14]计算井筒A环空带压临界值,考虑多种因素随服役时间变化情况,如式(1)~式(10)所示[26-27]。
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