Cementing Job - Preparation Guidelines

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This article presents guidelines for: 1. Treatment of Mud Prior to Cementing, 2. Hole Volumes and Slurry Volume Calculations, 3. Circulation Test before the job.

Treatment of Mud Prior to Cementing

Before pulling out of hole to run casing, the hole shall be circulated clean (150 % of casing contents) until there are no further cuttings returns at the shakers. This shall be witnessed by the Mud Engineer and Mud Logger.

To improve displacement efficiency, the mud shall be conditioned to reduce the rheology during circulation, if needed.

Solids control equipment shall be run to remove drill solids from the mud thus reducing PV to the lowest practical level.

Dispersants / thinners shall be added to reduce the YP and 10 minute gel strength. (YP not reduced in high angle wells)

The mud must be completely free of gas after circulating. Circulation must be continued until a full annular volume has been pumped with no indication of gas.

Hole Volumes and Slurry Volume Calculations

Cementations shall be based on volumes calculated from a calliper log (plus 10% excess) if available. This is particularly important for cementations across hydrocarbon zones

If off‑scale washouts occur, make a best guess of hole volumes. Most calliper logs will give an integrated hole volume and an integrated cement volume. The amount of excess to be added has to be considered for each individual case. Four arm calliper tools are preferred as they are more accurate. The calliper should be run inside the previous casing shoe as a check. In the case where an integrated hole volume is given, the tool should be run for at least 100 ft inside casing.

Circulation Test

Prior to a plug type cementation, at least 150 % of the casing content must be circulated. During this circulation the circulating pressures at different pumping rates for each pump shall be recorded.

Commence circulation at a very low rate.

Increase flow rate in increments of 2 bbls/min or to limitation due to ECP’s.

After each increase, wait at least five minutes to observe for losses and to allow pressures to stabilise. Ensure the tank level indicators are properly working and physically check the level in the active tank.

Reduce the pump rate as soon as losses are observed or as soon as the maximum equivalent circulating density (ECD) is reached.

In addition, a check shall be made on the circulation pressure at the rate that will be used to bump the plug, in order to observe the pressure differential and thus estimate the top of cement (TOC).

Notes:

The surface pressure losses through the wellhead and return surface lines must be included. No general rules can be given for these pressure losses but their value should be expected to be in the range of 100 psi at high circulation rates.

If losses are observed at a rate substantially below the maximum rate as predicted with regard to ECD considerations, and the corresponding annular velocity is not high enough to meet the displacement requirements, consideration should be given to circulating around a lost circulation material (LCM) pill. This should be carried out at a rate where slight losses are induced. Once the losses have stopped, the rate can be carefully increased in the increments outlined in the guidelines above. The cement should then be displaced later at 95 % of the maximum rate achieved without incurring losses.

When running 7” hydraulic hanger and ECP circulation rate and pressure depends on rating of shear pins

Coarse LCM is not to be used before cementing due to risk of plugging the float equipment

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