Posted on Oil & Gas
By: Ing. Andrés Marcano – CEMENT SPECIALIST
The reasons why cement plugs should be pumped, can be divided within four (4) categories:
- Deviated Plugs: It is recommended to use high density slurry between 15-17.5 PPG, with 0% free water, near zero ppg sedimentation and high compression resistance (greater than 500 PSI), always higher than compression resistance of formation). Operationally speaking 300 ft long plugs are recommended taking into account that it is estimated 25% of its contaminated length at the top and 25% at the bottom.
- Isolated cement plugs: Low density and low viscous slurry are recommended to avoid losing cement to formation. Important to cover at least 50 feet above and 50 feet below the zone to be isolated.
- Lost circulation plugs: It is recommended to use viscous slurry with a high gel resistance, this is achieved with high concentrations of Filter Controller (Polymers), and Retarder agents according to the formation temperature and operation time, plus LCM additives to reduce the flow to Vugulares and/or fractures. It is recommended to pump a preflow of 10 Bbls with 10% calcium chloride followed by 30 bbls of sodium silicate and then the volume of cement that will depend on whether the loss is partial or total.
- Well abandonment plugs: It is recommended to use low density and viscous slurry to avoid losing cement towards formation. The abandonment drilling program should be adapted to meet of local government agencies.
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