Study On Plugging Mechanism And Plug Removing Of Oil Well's Sand Control Area In Polymer Flooding Region

Polymer injection is an important measure to raise recovery ratio. With the application of polymer injection technology, there are some new technical problems coming forth, such as injection pressure lifting, sand production, or even borehole wall sloughing, casing failure, oil well abandoning, which affect oil production rate and hydrocarbon recovery.Some analysis was done by use of X-ray diffraction, microscopic and plasma emission technique in this paper. Through the analysis of bulkhead and produced water in immediate vicinity of wellbore, it has been found that the main composition is mineral and polyacrylamide. With the adsorption of HPAM with insoluble inorganic salt as colloidal nucleus, radius of formation fines was increased and void between the sand decreased, then the plug generated. Through morphological analysis and surface composition analysis of filling sand and flowback sand, it has been found that the primary cause made control sand layer banked-up is the rise of fluid viscosity after injecting polymer solution. This may lead to drag and carry the fine particle of rock surface strongly, and make that HPAM adsorbs and assembles on the sand surface. In the process of formation fluid flow behavior, aggregation of small size sand is obvious. In addition, migration of crude oil and mineral substance particulate could also cause formation damage.The simulation experiment was carried out in lab and it was found that the HPAM was strongly adsorbed on the surface of the sand. The adsorbance got to balance gradually and reached saturation adsorption over 20 days. The adsorption process is related to molecular weight and concentration of HPAM and salinity of displacing fluid. Under the same condition, bigger molecular weight and higher sand-to-agent ratio will result in adsorbed layer thicker and adsorbance bigger. The influence of solid-to-liquidratio and adsorption time to adsorbance was investigated. Furthermore, the adsorption isotherm of HPAM on the sand was given. It is according to extended langmuir adsorption.Plug removing agent named FSAY was synthesized and studied. It showed that the polymer block could be removed in immediate vicinity of wellbore effectively. Then the condition of the oxidative degradation was simulated in laboratory. The best process condition was obtained. First of all, the bulkhead was degraded with 4% water block remover and 5% hydrochloric acid within 48h. After that, acidizing bulkhead with mixed acid within 24h, and the proper ratio of water block remover and initiating agent and mixed acid is 1:1:1.In order to extend the effect and prevent polymer blocked again, a new type of protective agent named FSAF was used. After it was used in control packed layer, the plug was removed efficiently and the technology of removing plug was improved greatly.