This paper proposes an integrated technology of chemical sand control and stratified water injection in water injection well, which enlarge the inner diameter of injection well after sand control and achieve flexible stratification of injection layer. Mechanical sand control is the main method for injection wells in offshore oilfields. After sand control, the inner diameter of injection well is small and the number of injection layers is generally 3-4 layers. For reservoirs with strong longitudinal heterogeneity, it's difficult to get higher longitudinal sweep coefficient of driving and better effect of injection.
The technology realizes completion by chemical sand control, without screens downhole. The ceramsite whose surface has been treated by crosslinking agent is injected into the well and heated. The crosslinking reaction occurs on the surface of the ceramsite, forming a cement layer with a thickness of 3-5cm and a certain compressive strength of 7.2MPa and a permeability of 5000mD on the wellbore. This cement layer not only can be used as a barrier to retain formation, but also can provide flow channels for fluids. Then, the stratified injection pipe string is run. The developed multi-functional packer contacts and seals the cemented layer to realize the stratification of the injection reservoir. The position and quantity of the packer are designed according to the target injection horizon to achieve flexible stratification.
This technology has been successfully applied to 4 wells in the Bohai Oilfield, all of which have the characteristics of large reservoir thickness and strong vertical heterogeneity. The conventional sand control and injection technology makes it difficult for the actual injection volume to reach the target volume, and the water cut of the benefit well continues to rise. After applying the integrated technology, for a directional well with a bore diameter of 9.625 in, the maximum inner diameter can reach 9.625 in, while the inner diameter of traditional sand control methods is only 4.75 in. The number of injection layers exceeds 5, and the actual injection volume meets the designed requirement. The validity period has exceeded 40 months and continues to be effective. The water cut of the benefiting well decreases from 85% to 78%, and the oil production rate increased from 56 m3/d to 72 m3/d.
The successful application of the integrated technology provides a new idea for subdivision water injection in offshore oilfields. The increase in the internal diameter of well can reduce the difficulty of operation and increase the water injection rate. The flexible stratification can improve the vertical production degree of reservoir water flooding and the overall effect of water injection.