阿姆河右岸酸性气田井口冲蚀及对策

Analysis of and strategies for wellhead erosion in sour gas fields on the right bank of the Amu Darya River

中亚土库曼斯坦阿姆河右岸气田群为高含H_2S和CO_2的碳酸盐岩气藏,单井产量高,井口设备均出现了不同程度的腐蚀。初步分析认为其原因是生产过程中仅考虑酸性介质对气井井口的化学腐蚀,而没有考虑气体流速对井口的冲蚀作用,极大地影响了气田的安全生产。为此,通过对节流阀上下游阀道、法兰面均出现明显坑状腐蚀的进一步分析,明确了化学腐蚀和气体冲蚀的交互作用是井口磨损的主要影响因素,气流冲刷腐蚀坑的化学腐蚀产物会加速冲蚀损害;进而借鉴冲蚀与腐蚀运行环境下的多相管流管道的磨损计算理论,计算了该运行环境下的冲蚀极限速度,得到了不同生产工况下节流阀的抗冲蚀流量;最后,根据气田生产情况,针对性地提出了按气井配产要求来选择采气树类型、节流阀通径及类型冲蚀的技术控制策略。此举为气田安全生产提供了工程技术保障。

Most carbonate gas reservoirs with high content of H2 S and CO2 have been found in the right bank of the Amu Darya Riv- er, Turkmenistan, Middle Asia. Although the single-well production is very high there, wellhead equipments have been corroded in different degrees. A preliminary analysis indicated that the production safety of a gas field in this study area will be threatened not only by the chemical corrosion at the wellhead resulting from certain acidic media but by the wellhead erosion from gas flow rate. In view of this, we analyzed the obvious pit-shape erosion emerged in upstream and downstream valve paths and flange surfaces of throttle valves and found that the main factor of wellhead erosion is the interaction between chemical corrosion and gas erosion and that the erosion will be accelerated when air flow washes the chemical products of a corrosion pit. In addition, on the basis of the erosion calculation theory of a multi-phase flow pipe in an erosive and corrosive operating environment, we calculated the critical erosion velocity in the operating environment and obtained the anti-erosion flow rate of the throttle valve under different working conditions. Finally, according to gas field production status, we recommended that the Christmas tree type and the drift diameter and type of a throttle valve should be selected based upon the production allocation of a gas well, providing technical and engineering support for the production safety of gas fields in this area.