渤海凝析气田环空带压预测及管控研究

Prediction and control of annulus pressure in Bohai condensate gas field

渤海某凝析气田服役环境恶劣,具有中含CO_(2)和微含H2S、超高温(最高井底温度>200℃)、井身结构复杂、初期产量高(最高设计产量25×10^(4)m^(3)/d)、计划服役时间长(>20年)等特点,极易诱发环空带压,严重威胁该气田气井的井筒完整性安全。基于API RP90(2021)、ISO/TS 16530-2以及中国海油Q/HS 14031等标准,结合该气田特点,考虑温度效应、鼓胀效应等影响环空体积的因素,建立了适用于该凝析气田开发初期的环空带压值预测方法以及考虑关键节点(包括井下安全阀、封隔器等屏障单元)承压能力的环空带压控制值,提出了相应的环空带压管控措施,为该气田安全生产提供理论支撑及决策依据。研究表明,该凝析气田开发初期环空带压由高产带来的温度变化引起,其控制值由组成环空最薄弱点的强度决定,如X井A环空薄弱点为4617~4690 m段φ177.8 mm尾管,其环空带压控制值取决于φ177.8 mm尾管的抗内压能力,控制值最小为36.66 MPa,X井整个生产过程不会发生环空带压失效问题;尾管若换为碳钢材质,环空带压预测值将会在第13年超过控制值,发生环空带压失效问题。本文研究成果可为海上气田环空带压管控和管柱选材提供参考。

The safe development of one offshore gas field is crucial to increasing production and storage capacity in China.Its service environment is harsh,for it is characterized by moderate CO_(2)content and slight H2S content,ultra-high temperature(maximum bottom temperature exceeds 200℃),complex wellbore structure,high initial production(maximum design production reaches 25×10^(4)m^(3)/d),and long planned service time(>20 years).These characteristics can easily induce annular pressure,which seriously threatens the integrity and safety of the wellbore of the gas wells.Therefore,based on the standards of API RP90(2021),API RP90-2 and CNOOC Q/HS14031,the characteristics of the gas field are combined and factors such as temperature effect and bulging effect that affect the annulus volume are considered in this paper.A prediction method for the annulus pressure value suitable for the early development stage of the gas field is proposed.Besides,an annulus pressure control value that considers the pressure bearing capacity of key barrier units(including downhole safety valves,packers,and others)is established too.Corresponding annular pressure control measures have been proposed to provide theoretical support and decision-making basis for the safe production of the gas field.According to research,the annular pressure in the early development stage of the gas field is caused by temperature changes due to high production.The control value of the annular pressure is determined by the strength of the weakestpoint in the annulus.For example,the weak point in Annulus A of Well X is the 177.8 mm liner in 4617-4690 m,and its control value of the annulus pressure depends on the burst strength of the 177.8 mm liner.The minimum control value of Well X is 36.66 MPa,and the entire production process of Well X will not experience annular pressure failure.But if the liner is replaced with carbon steel material,the predicted value of annular pressure will exceed the control value in the 13th year,leading to the problem of annular pressure failure.The research results of this article can provide reference for the control of annular pressure and the selection of string materials in the offshore gas field.