Fishing and remediation technology for complex falling objects in volcanic monitoring fluid observation well

Abstract:

Due to instrument sticking and a previous failed fishing operation， a fluid observation well at a volcanic monitoring station was left with various complex fish， such as drill pipes and cables. Furthermore， the operation was strictly constrained by the high-altitude scenic location and environmental protection requirements. To address these complex well conditions， a downhole television system was used to accurately locate the top of the fish， and a combination of techniques-fishing， back-off， milling， and washover milling-was applied for well remediation. During the operation， external force was applied to increase torque， and a left-hand tapered tap was used for thread making and back-off， successfully backing off the stuck drill string. A customized washover tool with a wire-reel barrel was developed and innovatively modified （by welding steel bar hooks on its inner wall） to clear entangled cables and assist in fishing the drill tools. Finally， pin joint connection fishing and external hook fishing were employed to recover the remaining cables. Meanwhile， a high-viscosity drilling fluid was formulated for cuttings removal， and a closed-loop system was established to achieve zero discharge of drilling mud. As a result， all downhole fish were successfully retrieved， including a total length of 173.44 m of stuck drill pipes， along with all cables， instruments， and fishing hooks， achieving a 100% fishing success rate. The wellbore sustained no secondary damage， the function of the observation well was fully restored， and economic losses of nearly 2 million RMB were saved. This study provides referable technical approaches and practical experience for the fishing and remediation of complex fish in similar troubled wells.