Online Monitoring and Automatic Control for Zonal Polymer Injection Wells

摘要

Polymer flooding has been improved an effective way for EOR in China. Comparing with waterflooding, zonal pressure and flowrate change much larger for polymerflooding duo to its high viscosity. Reservoir engineer are required to adjust flow allocation scheme frequently when pressure change. However, traditional zonal polymer injection technique can not obtain zonal parameters during injection process. The flowrate adjustment has been done by fishing downhole choke by steel wire. Usually, the fishing operation was implemented many times. The efficiency is poor. This paper introduced an online monitoring and automatic control technology. A instrument was used to realize zonal polymer measurement and adjustment. There is no need for downhole fishing tool. Considering viscosity decrease control, a downhole streamline slot adjustable choke was development. The lab test indicated the viscosity decrease rate can be controlled within 10% when flowrate vary from 10-60m3/d. At the same time, the flowrate can be adjusted according to set point by instrument. And it can also be regulated at any time manually just needing pushing the mouse in the office. This technology has been applied more than 200 wells in Daqing. The downhole instrument is mainly consisted of mechanical arms, control part, measuring part and guiding mechanism. Comparing with waterflooding, the torque output for polymer injection well is much larger. Torque output of water flooding is only 3-5N.m, however, it can increase by more than two times to 8-12N.m for polymer flooding. Meanwhile, on-line torque monitoring function is added to effectively prevent excessive current that damages the motor and adjustment success rate. Considering the flowmeter based on internal magnetic may result in polymer blocking, external magnetic type flowmeter was used to avoid affects due to polymer plugging. The technology has been applied in 60 polymer injection wells by the end of 2016 and the test time of average single well is shortened from 5.2 days to 2.5 days which means the efficiency is more than two times higher. At last, a case study was introduced.