井口冷冻暂堵技术在苏北油田的应用

Application of Wellhead Freezing Temporary Plugging Technology in Subei Oilfield

苏北油田自2005年开始进行CO_(2)驱油先导试验,随着生产时间的增加,部分油气井井口装置出现密封件老化、腐蚀磨损等问题,发生井口泄漏。传统治理方式主要有压井和堵塞器作业等,存在伤害储层、成功率低等缺点,适应性较差。为了解决井口泄漏问题,决定研究并应用井口冷冻暂堵技术。对相关工艺参数进行优化研究,冷冻温度确定为低于-20℃,以干冰作为冷冻剂;以蒙脱石为主要成分的膨润土作为暂堵剂,确定水、膨润土和添加剂的最佳质量比为5∶2∶1,并计算暂堵剂用量;在表层套管规格为φ244.5mm条件下,初步确定冷冻时间为20h。冷冻桥塞强度测试结果表明,冷冻桥塞的抗拉力、抗剪切力和承压能力均符合要求,可以满足现场施工需要。在注气井C21井和注气受效油井L1-15井成功完成现场应用,C21井设计冷冻桥塞长度为2m,顺利更换了井口泄漏部位。冷冻暂堵技术对储层无污染,施工成本低,成功率高,为注气井及注气受效油井井口隐患处理提供了技术支撑。

Subei Oilfield began to conduct CO2 flooding pilot test in 2005.With the increase of production time,some wellhead devices of oil and gas wells have problems such as aging seals,corrosion and wear,resulting in wellhead leakage.The traditional measures mainly include well killing and plugging operation,etc.,which has the disadvantages of reservoir damage,low success rate and poor adaptability.In order to solve the problem of wellhead leakage,it is decided to study and apply the temporary plugging technology of wellhead freezing.The related process parameters are optimized.The freezing temperature is determined to be below 20℃,and dry ice is used as refrigerant.Bentonite whose main content is montmorillonite acts as temporary plugging agent,the best mass ratio of water,bentonite and additive is determined to be 5:2:1,and the dosage of temporary plugging agent is calculated.Under the condition that the surface casing size is 244.5mm,the freezing time is preliminarily determined to be 20h.The strength test results show that the tensile force,shearing resistance and bearing capacity of the frozen bridge meet the requirements,and can meet the needs of site operation.Field applications are successfully completed in gas injection well C21 and oil well by effective gasini jection L1-15.The designed length of frozen bridge for Well C21 is 2m,and the wellhead leakage site issuccessfully replaced.Freezing temporary plugging technology has no pollution to the reservoirs,low cost,high success rate,and provides technical support for wellhead hidden danger treatment in the gas injection wells and effective oil wells by gas injection.