ABSTRACT
After a long run of water flooding recovery, the near well areas of the Weixing oil fields were blocked by a large amount of colloids, asphaltenes, and paraffin, resulting in yield decline of the oil wells. There is an urgent need to explore new technologies to mitigate oil production decline and increase single well production. The results of microbial reservoir adaptability evaluation indicate that the microbial huff-and-puff test is suitable for Weixing oil fields. Eleven pilot test wells were selected according to the well selection principle, and one strain of Bacillus subtilis with good compatibility with the reservoirs was selected, which could metabolize biosurfactant and reduce the surface tension to 28.85 mN/m. The corresponding huff-and-puff scheme is designed according to the production status, pay-zone thickness, treatment radius, and porosity. After microbial huff-and-puff, it was effective in 10 wells, accounting for 90.91%. The daily fluid production rate was increased from 28.2 t/d before the huff-and-puff to 63.4 t/d after the operation and the oil production from 9.7 t/d to 25.0 t/d. The effect lasted for 240 days, accumulatively increasing oil production by 2048 tons and the input-output ratio reached 1:4.9. After the treatment, the bacterial concentration in the produced fluid rose significantly to more than 107 cfu/mL, indicating that the injected microbial strain grew well in the target reservoirs and had great oil-increasing potential.
