Process Optimization Research And Application Of Fuzzy-ball Workover Fluid In Jingbian Gas Field

Having been exploited for many years,well workover operation is constantly conducted in a great number of natural gas wells in Jingbian gas field due to reservoir reconstruction and well maintenance.In order to guarantee the security,well killing is adopted to maintain the well’s stability before well workover operation.Meanwhile,the well killing operation shall reduce its damage to reservoir to the minimum,keeping a steady production.According to the literature,researchers at home and abroad endeavored to reduce the damage to reservoir while ensuring safe operation.A large quantity of research focused on well killing construction method optimization and well killing fluid system and had made some achievements regarding different applied conditions.However,the research mentioned above mainly aimed at the two aspects respectively instead of combining them to resolve the problem.This resulted in the fact that many experiments could not efficiently provide guidance for the field practice and a great many operation processes were not extended.The reservoir in Jingbian gas field was a carbonate gas reservoir characterized by low porosity,low permeability,low reservoir pressure coefficient,high temperature and sulfur component.The laboratory experiment demonstrated that the main vulnerable factors of Jingbian gas reservoir were the reservoir pressure change.Through comprehensive analysis of the gas field’s reservoir characteristics as well as reservoir sensitivity,villus cyst fluid was chosen as the well killing fluid by virtue of laboratory experiment.Given the specific condition of the gas reservoir in Jingbian gas field,villus cyst fluid well killing process optimization experiment was conducted.The laboratory result demonstrated: high-viscosity villus cyst fluid worked as fluid piston inside the wellbore due to its strong structural force while the low-viscosity was more suitable for blocking off the reservoir fluid because of its stability;the restored energy in the well killing process was beneficiary to enhance the flowback efficiency and reduce the damage to the reservoir.The field experiment proved that: the application of villus cyst fluid in well killing process without bleeding off pressure was able to achieve non-contact well killing operation to the maximum extent,thus maintaining the security and reducing the damage to the reservoir.Hence,the study verified the practical value of villus cyst fluid applied in the well killing process and significance for same-type well killing operation.