Abstract
Most of the failures in primary cementing are attributable to "channeling", an imperfect displacement of mud with cement slurry. Water or phosphate added water works to some degree as a spacer between mud and cement slurry but its function as "channeling" preventive is negligible. Its use also presents a problem of pressure balance in primary cementing.
The objective of the authors have been to develop "an effective preflush fluid" that solves the problem of channeling.
Preflush fluid should have the following qualities:
1. Early destroying performance against mud gel strength.
2. Good suspending capacity.
3. No adverse effect on cement slurry.
After repeated experiments along this line, a satisfactory preflush fluid has been developed by using a kind of surfactant. The density of this fluid may be increased up to 2.0g/cm3 adding with fly ash and barite. And such weighted fluids solve a problem of pressure barance. As this fluid has a washing effect on the surfaces of casing pipe and formation, it may be utilized as an excellent means of improving cement-bonding.
