Research On Scaling And Relative Prediction Method Of Separated Layer Water Injection In QD Oilfield

Separate layer water injection is a very important method in heterogeneous reservoir development and has been widely used in Daqing, Shengli, Zhongyuan oil field, etc. Compared to commingled production method, it controls rising water-cut and improves oil recovery. But the produced water reinjection caused many problems, such as pipe string corruption, scaling, permeability decline and so on. This paper research on QD oilfield in Shengli, the current exploitation status and reinjection water properties were analyzed. The compatibility of reinjection and formation water in different blocks in QD oilfield, reinjection water stability in different temperatures, scale sample X-ray analysis and mineral composition analysis were tested. The calculation and prediction models of scaling on water injection line and pipe string were built based on kinetics principles and theory of two-phase flow. Formation scaling was also calculated to describe the influence of water scaling on injection pressure and water volume. As to the pipe string structure, scaling in packer, bottom ball, water nozzle were analyzed. Carbonate precipitation, iron corrosion and microbe stirring up problem are main reasons of reinjection water scaling. To improve reinjection water quality, optimizing water treatment, adding anti-scaling agent and replacing with glass pipe are useful methods to avoid scaling. According to scaling prediction model, the longer the water flooding, the deeper the oil pipe, the higher the reservoir temperature, the thicker the scaling thickness. It also proves that after long period water flooding, the oil reservoir permeability declines and water injection pressure will become twice or more than initial one in five years when the injection volume remains unchanged. Also, injection volume will decrease quickly when the injection pressure stays the same. This research analyzes the failure reasons of separated layer water injection, establishes scale prediction method of water injection line, pipe string and reservoir formation, optimizes pipe string structure and ameliorates separate injection efficiency. It’s also meaningful to the sustainable development of other oilfields.