Analysis on the causes of casing mud return after cementing

Analysis on the causes of casing mud return after cementing

After cementing, the phenomenon of casing slurry return often occurs in cementing operations of major oilfields. There are many factors causing this phenomenon, and the common factors are mainly from the following points.

1、 Insufficient mud treatment

During the well circulation before cementing, the mud constantly washes the sealing valve core of the float collar and float shoe. At this time, if the mud treatment degree is not enough and contains large particles of sand or impurities, after a long time of flushing, the rubber sealing ring mechanism of the valve core will be damaged, thus affecting its sealing effect. Before running the casing, filter with sand by displacement. If the particles are too large, the screen of vibrating screen should be replaced in time.

2、 Insufficient mixing of cement slurry

During cementing operation, cement and water are mixed to form cement slurry and then injected into casing. At this time, if the cement slurry is not fully mixed and contains large cement blocks or particles, the valve core mechanism of float collar and float shoe will also be damaged. It is also possible that after cementing operation, when the valve core of float collar and float shoe is closed, the block or granular cement is clamped in front of the valve core and sealing surface, so that it can not be closed normally, resulting in cracks, thus affecting the sealing.

3、 Bump pressure requirements

In general, the cementing operation manual will have detailed requirements for the operation before and after cementing bump. For example, the displacement displacement before bumping is less than 0.8 m3 / min when the plug is replaced to prevent damage to the float collar.