低渗透CO_(2)驱注入井注入困难原因分析与防治对策

Analysis on the Causes of Injection Difficulties in Low-permeability CO_(2) Flooding Injec⁃tion Wells and Countermeasures

CO_(2)的平稳注入是低渗透油藏CO_(2)驱扩大波及体积与提高采收率的保障,针对CO_(2)驱注入井、水、气交替过程中陆续出现的油管缩径、油管堵塞、近井油层堵塞等引起的注入困难问题,依托注水管线冲洗、连续油管冲洗返吐等方式,对储层、井筒、井口、管线等重要节点,开展了岩心、水质、固体沉积物、堵塞物取样分析,结果表明:由于注入水水质不合格,含油、机杂以及FeCO_(3)、FeS、CaCO_(3)等腐蚀结垢产物的二次污染是引起注入困难的主要原因。根据不同堵塞位置,优选设计了连续油管热洗+钻磨、连续油管旋转喷射+解堵液等解堵治理技术与措施,有效解除了井筒及近井地带堵塞现象。同时,针对欠注原因,优选了防腐药剂体系,配套了接力加药工艺与井口过滤器,形成了日常防控技术措施,保障了地面管线内防腐效果与入井流体合格,减少了管线、井筒、地层二次污染。通过防治技术相结合,保障了CO_(2)驱注入系统高效、平稳注入。

The smooth injection of CO_(2) is the guarantee for the expansion of swept volume and enhanced oil recovery of CO_(2) flooding in low-permeability reservoirs.In view of the injection difficulties caused by tubing shrinkage,tubing plugging,and near-well reservoir plugging during the water-gas alternations of CO_(2) flooding wells,the methods of water injection pipeline flushing,and coiled tubing flushing and backflow are adopted.Samples of core,water quality,solid sediment,and blockage are analyzed for important nodes such as reservoir,wellbore,wellhead,and pipeline.It is found that the injection water quality is not qualified,the secondary pollution caused by oil,impurities,and corrosion and scale products such as FeCO_(3),FeS,and CaCO_(3) are the main cause of injection difficulties.According to different plugging positions,the plugging removal technologies and measures such as coiled tubing hot washing+drilling and grinding,coiled tubing rotary injecting+plugging removal fluid are optimized,which effectively removed the plugging phenomenon in the wellbore and near the well.At the same time,for the reasons of insufficient injection,the anti-corrosion agent system is optimized,the relay dosing process and the wellhead filter are matched,and the daily prevention and control technical measures are formed to ensure the anti-corrosion effect in the surface pipeline and the qualification of the fluid entering well,reduce the secondary pollution of the pipeline,wellbore,and formation.Through the combination of prevention and control technology,the efficient and stable injection of the CO_(2) flooding injection system is ensured.