HPHT Consistometer

During cementing operations, the time required for a cement slurry to set is of primary concern. Under an ideal situation, minimal time would be required to successfully pump the slurry, which immediately upon placement, begins to develop compressive strength. However, if insufficient time is allowed to fully pump the cement, it will be necessary to drill the cement remaining in the casing string. Remedial operations such as this are very costly. Conversely, cements that are successfully placed, but require considerable time to cure, consume valuable rig time, which is also quite costly. Laboratory tests should be conducted under simulated reservoir conditions to examine the actual thickening time of the slurry. The OFITE HPHT Consistometer was specifically engineered to determine the thickening time of well cements under simulated downhole pressures and temperatures.

Method of Operation:
A cement is mixed and poured into the slurry cup assembly. The slurry cup is placed into the test vessel and pressure is increased via an air-driven hydraulic pump. A PID temperature controller governs an internal heater, which maintains the necessary temperature profile, while a magnetic drive mechanism rotates the slurry cup assembly at 150 rpm. A potentiometer controls an output voltage, which is directly proportional to the amount of torque the cement exerts upon an API-approved paddle. A dual channel strip chart recorder registers cement consistency and temperature as a function of time. Temperature and consistency are digitally displayed via LED indicators.

Features and Specifications:
-Maximum operating temperature of 600°F/400°F
-Max. allowable working pressure of 40,000 psi/25,000 psi
-Digital temperature controller, 1° resolution
-4,000 watt internal heater (5,000 watt available)
-Pressure indicator resolution is 100 psi and incorporates high and low pressure alarms
-Slurry cup rotational speed is 150 rpm
-Pressure generated via an air-driven hydraulic pump
-Slurry cup constructed of 316 stainless steel and incorporates an expansion chamber
-Drive table is rotated with a magnetic drive
-External cooling jacket aids cooling of test cell
-Electronic timer with alarm, elapsed 0.1 minute resolution
-Deadweight calibration unit included

Mud Balance

The mud weight may be determined using any instrument that will permit accurate measurement within 1/10 lb/gal or ½ lb/cu. ft. The mud balance is the instrument generally used. Mud weight can be expressed in lb/gal, lb/cu. ft., psi/1000 ft. of depth or specific gravity (S.G.).

Procedure:

. Fill the cup with the mud to be weighed.

2. Place the lid on the cup and seat it firmly but slowly with a twisting motion. Be sure some mud runs out of the hole in the cap.

3. With the hole in the cap covered with a finger, wash or wipe all mud from the outside of the cup and arm.

4. Set the knife on the fulcrum and move the sliding weight along the graduated arm until the cup and arm are balanced.

5. Read the density of the mud at the left-hand edge of the sliding weight.

6. Report the result to the nearest scale division in lb/gal, lb/cu ft, S.G., or psi/1000 ft of depth.

7. Wash the mud from the cup immediately after each use. It is absolutely essential that all parts of the mud balance be kept clean if accurate results are to be obtained.

Calibration:

The mud balance should be calibrated frequently with fresh water. Fresh water at 70º F will give a reading of 8.33 lb/gal or 62.3 lbs/cu ft.

To adjust the mud balance to the proper reading, add or remove lead shot from end of balance arm or adjust set screw at the end of the balance arm.

The cement slurry weight may be determined using mud balance.