Analysis of Oil Well Blockage in K Oilfield in Kazakhstan and Blockage Removal Techniques

Blockage of tubing and casing was found in thedown hole of K oilfield, which seriously affected the production job. The type of the blockage was identified and a high efficiency chelating blockage removing agent was developed to addressthe problem. After identifying the composition of the blockage, the reservoir characteristics of the K oilfield were first analyzed toascertain the potential reasons of well blocking. It was found that scales and the peeling iron rust by CO₂ corrosion were the possiblereasons of well blocking. Then, using XRF and XRD instrument, the main components of the blockage was determined, and they are ferricoxide and small amount of rock salts. Finally, by dissolving the blockage in various acid solutions, the type of the blockage wasfurther confirmed. A blockage removing fluid, made up of an optimized chelating agent, hydrofluoric acid and a corrosion inhibitorfluid, were then developed. It was found that theblockage removing fluid works well at 120℃ and has no harm to the N80 coupon. The dissolved ratio of the blockageis 82% in 2 h.This blockage fluid cannot only protect tubing/casing strings but also dissolve the blockage, and it show excellent blockage removing abilities. After adding a corrosion inhibitor KMS-Z, its corrosion rate reduces to 8.91 g/(m²·s), which exceeding the Class 1 of corrosionindustrial standard requirement. On the other hand, although mud acid have good dissolving ability to the blockage, it is unable to control corrosion rate. Failure of corrosion protection in mud acid maybe come from the strong oxidizing ability of the ferric ions.