连续油管作业已经成为油气井开发过程中较为普遍的作业,但是在冬季,尤其是夜间,连续油管作业时,井筒内的天然气和地层流体沿着井筒上返的过程中,温度逐渐降低,在一定的压力条件下会形成天然气水合物,这种物质会堵塞连续油管作业中的流体返出通道,从而造成连续油管遇卡,严重时可能带来井控安全风险。为此,从天然气水合物产生的原因入手,结合现场作业实践,分析了冰堵成因、危害、判断方法及防控措施,研究结果表明：①温度和压力、流体饱和度、井筒内的砂粒或钻屑等物质、流动条件的突变等因素均为冰堵成因,在井口附近、防喷器、防喷盒和防喷管等处最易出现冰堵。②冰堵可能导致井下工具遇卡、应力腐蚀、管柱损伤、井控设备失效等危害。③冰堵的判断,最易产生冰堵的连续油管作业工艺主要有两种类型,一是需要向井筒泵注液体并循环出井口的工艺,如钻磨、冲洗解堵作业;二是地层有液体和气同时沿着井筒返出地面的工艺,如速度管柱作业。作业期间发生冰堵,可以通过观察工艺参数的变化异常情况来进行判断,以便及时采取有效措施。④冰堵的预防、控制措施,物理方法如蒸汽加热、用工业防爆电热毯或电加热带保温、泵注热水等,化学方法为添加化学抑制剂（如乙二醇、除硫剂、CaCl2等）,实际是使用上述一种或几种方法的复合方式以预防或控制冰堵,同时从连续油管作业过程中的具体工艺技术方面,提出了可采取哪些技术细节措施以防控冰堵。将上述研究成果应用于现场,通过4口井连续油管作业期间发生异常,判断为冰堵后采取相应措施、成功解除冰堵的案例,证明研究成果有效,能为现场连续油管安全作业提供技术保障。
Coiled tubing operation is popular in the development of oil and gas. However, during the operation in winter, especially at night, the temperature of gas and formation fluid drops while flowing to the surface along wellbore. Gas hydrates may be formed at a certain pressure, blocking flowback channel. Thus, the coiled tubing may be stuck, resulting in safety risks in severe cases. In this study, the causes, hazards, diagnosis methods and preventive measures of ice blockage were analyzed based on the causes of gas hydrates, as well as the field operations. Results show that, (1) ice blockage can be formed by factors including temperature and pressure, fluid saturation, sand particles or drill cuttings in wellbore, and sudden changes in flow conditions; it is most likely to occur at the positions like wellhead, blowout preventer, blowout preventer box, and lubricator; (2) ice blockage may lead to downhole tool sticking, stress corrosion, pipe string damage, well control equipment failure and so on; (3) ice blockage is common in two types of coiled tubing operation: one is the process that liquid is pumped into wellbore and circulated out of wellhead, such as drilling, grinding, and flushing, the other is the process that formation liquid and gas flow together to the surface along wellbore, such as velocity string operation; in operation, ice blockage can be diagnosed by observing the abnormal changes of technical parameters, so that effective measures can be taken in time; and (4) the prevention and control measures include physical methods such as steam heating, thermal insulation with industrial explosion-proof electric blanket or electric heating belt, and pumping hot water, and chemical methods such as adding chemical inhibitors (e.g. ethylene glycol, desulfurizer, and CaCl2); in practice, one or more of these measures is/are usually used, meanwhile, specific control techniques are proposed depending on coiled tubing operations. The above research results were applied on site. The abnormality was observed in 4 wells during the coiled tubing operation, diagnosed as ice blockage, accordingly, proper measures were taken for blockage removal. The successful application proves that the research is effective and can provide support for safe operation.
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