Analysis of Under-injection in Injection Wells and the Countermeasures of Bohai Sea L Oilfield

Some water injection wells of Bohai Sea L Oilfield show that injection pressure increases rapidly and injection is difficult, and the amount of water injection can not meet the reservoir injection allocation. Therefore, the under-injection causes of injection wells in L Oilfield are analyzed. The reservoir rock sensitivity, drilling and completion fluids damage and injection water damage to reservoir are evaluated by core displacement experiments. The compatibility between injection water and formation water is evaluated by static compatibility test. The results show that the reservoir has strong velocity sensitivity damage and the water injection rate of some wells at initial stage is far more than critical injection rate of velocity sensitivity damage, resulting in irreversible particle migration damage. The core permeability damage rate of drilling and completion sequence operating fluids is between 35.5% to 48.2%, and that of single injection water is between 31% and 35.2%. The reservoir damage caused by solids invasion in drilling fluids and injection water quality exceeding the standard for a long time is the key reason for the generally poor injection capacity of injection wells in L Oilfield. It is suggested that new wells begin injecting after flowback or acidification should be carried out at initial stage to reduce the damage of drilling fluids. The initial injection rate should be controlled below the critical injection rate of velocity sensitivity, and the injection rate should be increased step by step to avoid the damage of particle migration. Meanwhile the control of key indexes such as suspended solids content, oil content and sulfate reducing bacteria in injection water should be strengthened.