Casing Failure In Unconsolidated Sandstone

The major oil fields in east China are currently being operated at secondary or thirdly period, i.e. enhanced recovery, which generally induce a serious sand production in unconsolidated sand. Therefore the cavity around the well casing structure may be enlarged by sand erosion mechanism in reservoir. This cavity will cause the reservoir instabilities and casing failure under unbalance load environment. The major works include the following:(1) From the research of sanding mechanism in unconsolidated sand, some important factors, such sand erosion, the strength damage and instabilities of reservoir structure during sanding, have been incorporated into sand prediction model. Then the sand perdition models, methodology, and quantitative analyses were updated.(2) A finite element code was devised to simulate sanding process and casing failure. To verify the suggested models and methodology, some practical field data from No. A23 well of Bohai oilfield was selected to compare with the models'results. The results show that the model has good prediction ability in sand production.(3) Considering the practical case of casing failure in unconsolidated sand, the interrelation between sanding process, erosion cavity and casing structure failure has been modeled into FEM software. The effects of in-situ stress, the pressure drawdown and the building-up time on the casing deformation were quantitatively simulated, respectively.(4) According to the simulating numeral results in this paper, some suggestions for production scheme was presented: including reasonable drawdown pressure, the balance between injection and production rate, refined sand control technique, and the casing structure strength.