Research of Formation Protection Technology in Complex Fault Block Oilfield

Abstract

Dagang Oilfield is a part of oil-gas reservoir with various reservoir types, broken fault block, high heterogeneity and complex geological situations. For example, in low pressure and high permeability reservoirs, permeability is higher than 2000 mD and pressure coefficient is less than 0.5. The salinity of formation water in low permeability reservoir is as high as 30000 mg/L, and the pour point of crude oil is as high as 40 °C. The statistics show that the average recovery time of the well yield after remedial work is over 7 days, and the average recovery rate of the well yield is less than 87% in Dagang Oilfield, which have an influence on the stable production and the benefit development of the oilfield. The problem above has not been effectively resolved for a long time because of the factors of technology and cost. In this paper, a series of low cost formation protection technology were developed. First, the low-cost nitrogen microbubble temporary blocking technology, which can block 2 mm aperture, was developed by improving preparation technology of nitrogen microbubble working fluid and adding degradable temporary blocking material. Second, the formation protection for complex low-permeability reservoirs was developed by enhancing the temperature of workover fluid and adding the high efficiency surfactants. The results show that the temperature of workover fluid increases by 20-50 °C. Finally, the low-cost workover operation technology with formation protection was developed. The cost can be reduced more than 50% while protecting the formation. So far, the all technologies were successfully applied in 2135 wells. After the application of technology, the average recovery time of the well yield is 3.5 days, the average recovery rate of the well yield is 96%, and the total production loss is 15.7 ° 104t. The problem of the formation pollution during the workover has been effectively resolved, which provides technical support for the production stability of complex fault block oilfield.