During setting stage the cement column doesn’t exert the hydrostatic pressure onto the formation any longer, and at this point gas migration can occur. Gas migration additives can prevent gas migration by reducing the matrix permeability of a cement system during the critical liquid to solid transition time and by improving bonding between cement/steel and cement/formation interfaces.
Application: Up to 93 degC
Description: Clear, off-white liquid
Primary purpose: The product is a harmless cationic high molecular weight polymer solution and is used to control or prevent gas migration after primary cementing and in critical cement plugs. It can only be used in combination with anionic additives like lignosulphonate retarders and/or friction reducers. Laboratory testing is recommended to determine type of friction reducer requested to prevent “synergistic effects” or precipitation. The freezing point of the product is minus 10 oC and can be lowered by additions of methanol. The pH is about 7.
Guidelines for use: Recommended: 5 to 20 liters per 100 kg of cement. Normally 10 liters are more than sufficient, depending on type, brand and quality of the cement.
Run laboratory tests under simulated field conditions in a HTHP consistometer and HTHP fluid loss test cell. Add retarders as needed to obtain sufficient pumping-time. Finally check for HTHP cement settling.
Suggestion: test slurry in HTHP consistometer for some time, less than the final thickening time, then transfer slurry to both fluid loss cell and to cement-settling-cylinder. When needed, add microsilica to improve rheology and/or settling.
It does not need anti coagulation additives.
It is a non-critical additive for cement and safe to use.
It can be used with Portland cement, Slagcement and Pozzolancement, with or without bentonite or attapulgite.
It is compatible with salt up to saturation.
It is compatible with Calciumchloride: it functions even better with 2% Calciumchloride.
Application: Up to 150 degC BHCT
Description: White liquid
Primary purpose: Latex additive that creates an impermeable barrier against the formation gas thereby preventing annular gas migration during the “transition”period of cement.
Guidelines for use: This additives is an aqueous dispersion of solid polymer particles including surfactants that add stability to the dispersion. The dispersed polymer particles block pore spaces between cement grains reducing permeability and restricting movement of gas through the matrix.
The additives improves the bond to casing and formation interfaces and promotes excellent fluid loss control.
It is effective for temperatures ranging from 66 degC – 121 degC, and may be used up to 150 degC BHCT.
Slurry can be prepared with fresh water or seawater. However, fresh water should preferentially be used when available on offshore rigs. Dispersants should be used in the mixture.