1
DYNAMIC SETTLING TEST
1.EQUIPMENT NEEDED TO PERFORM THE TEST
- Modified Slurry Cup Paddle.
All of the internal horizontal blades are removed from a standard API paddle for the HPHT consistometer. A flat disc (Figure 1) is then attached above the remaining bottom horizontal blade as indicated in Figure2 2 and 3.
Figure 1
Figure 2 /
Figure 3
B.Variable Speed Consistometer
1.The consistometer must have a variable speed drive that is capable of rotating at speeds of 150 rpm and 25 rpm.
2.Test Procedures for API Dynamic Settling Test
A.Prepare the cement slurry in the customary manner (normal API recommended procedures).
B. Place the slurry in a consistometer slurry cup which is equipped with the dynamic settling paddle. Note:Fill the cup from the top, and not in the conventional manner due to the design of the paddle.
C.Place the slurry cup in a variable speed HPHT consistometer.
D.Bring the slurry to the desired bottom hole circulating temperature and pressure conditions using the appropriate schedule while stirring at the API standard speed of 150 rpm.
E.Once the desired temperature and pressure conditions are reached continue stirring at 150 rpm for 10 minutes to be sure the slurry and equipment are stabilized at these conditions.
F.Reduce the stirring speed to 25 rpm and continue to maintain the final temperature and pressure conditions.
G.Observe the consistency and temperature response while continuing the test for at least 30 minutes at 25 rpm (30 minutes is suggested).
H.Continue stirring at 25 rpm and cool the consistometer as quickly as possible until a safe temperature to remove the slurry cup is reached (190°F or less).
I.Upon reaching a safe removal temperature, slowly release the remaining pressure from the consistometer.
J.Remove the slurry cup from the consistometer without inverting it. Remove the metal lock ring, blot the oil from above the diaphragm and remove the diaphragm (without removing the paddle) to allow for observation of the slurry inside the slurry cup. Record the condition of the slurry.
K.Carefully pour out the top 1/3 portion of the fluid into a beaker that has been previously tare on a balance. If the slurry does not flow easily, shake the cup gently to start the flow. Record the condition of the slurry.
L Place the beaker on a balance and from the volume of the slurry and its weight; estimate the density of the top portion of the slurry.
M. Carefully pour out the middle and bottom 1/3 portions of the fluid into beakers and similarly, estimate the densities of those slurry portions
N Once all the fluid has been poured out, carefully remove the paddle from the cup. Look for the presence of a cone of settled solids lying on the top of the plate. Record the height and condition of the cone if present.
M.With a spatula, cut a vertical section off of the cone of solids, parallel to the vertical bars of the paddle. Record the condition of the solids inside the cone. In cases of severe settling, segregation of different solid particles may be observed.
3.Test Evaluation
A.When the slurry is poured from the slurry cup, it should be uniform from the top portion to the bottom portion. Slurries having some differences in the viscosity and density from the top to the bottom, depending on the condition of the cone may be acceptable.
B.The coning properties are normally considered the most important portion of the test. A fully non-settling fluid will not develop a cone. Thus, a large, compacted cone is an indication of severe dynamic settling. After cutting off a section of the cone, sometimes a second cone is observed in the center (see Figure 5)). This is again is an indication of severe dynamic settling.
1.If there is a smaller cone in the center of the cone, the heights of the inner and outer cones and their appearances should be recorded. If the cone contains compacted settling, the slurry is considered to have a settling problem and slurries having compacted settling are normally not acceptable foruse, although slurries having no more than 1/16 inch compacted settling may be acceptable as long as there is no severe variation in the viscosity and density of the fluid slurry in the slurry cup from the top to bottom.
Figure 4
- Other test evaluationguidelines based on experiences using the test procedure
A true non-settling fluid will not form a cone on the bottom plate of the paddle (zero cone height). For cement slurries, some height of cone is normally observed. Experiences suggest that a maximum cone height that can be allowed is about 1/2 in.
For lightweight cement slurries, normally not more than 1/2 lb/gal difference from top to bottom of the cup is allowed. For weighted slurries (with hematite for example), normally not more than 1 lb/gal difference from top to bottom of the cup is allowed.