Mud Density
Mud density is commonly measured with a mud balance capable of ±0.1 lb/gal accuracy. A mud balance calibrated with fresh water at 70× ±5× should give a reading of 8.3 lb/gal.
Step 1. Measure and record the temperature of the sample of mud to be tested.
Step 2. Place the mud balance base on a flat, level surface.
Step 3. Fill the clean, dry, mud balance cup with the sample of mud to be tested. Rotate cap until it is firmly seated. Ensure that some mud is expelled through the hole in the cap to remove any trapped air or gas.
Step 4. Place thumb over hole in cap and hold the cap firmly on the cup. Wash or wipe the outside of the cup, and dry.
Step 5. Place balance arm on the support base and balance it by moving the rider along the gradu-ated scale until the level bubble is centered under the center line.
Step 6. Read the density (weight) of the mud shown at the left-hand edge of the rider and report to nearest 0.1 lb/gal. Enter result on API Drilling Mud Report as Weight (lb/gal, lb/ft3) or Specific Gravity.
Marsh Funnel Viscosity
Marsh Funnel viscosity is the time required (seconds) for a quart of mud to flow through a 2-in.
long, 3/16-in. diameter tube at the bottom of the Marsh Funnel. This viscosity measurement is used to periodically report mud consistency. One quart of water should flow through a Marsh Fun-nel in 26± 0.5 seconds.
Step 1. Hold one finger over the orifice at the tip of the funnel. Pour the mud sample through the fun-nel screen until mud reaches the bottom of the screen (1500 cm3). Place viscosity cup beneath funnel tip. Remove finger and start stop watch.
Step 2. Stop the watch when the mud level reaches the 1 qt mark on the viscosity cup.
Step 3. Record the number of seconds required to outflow 1 qt of mud. Enter on Drilling Mud Report as Funnel Viscosity (sec/qt) API.
Step 4. Measure and record temperature of mud sample to ±1×F.
Mud Density is used to control subsurface pressures and stabilize the wellbore.
Marsh Funnel viscosity is used to indicate relative mud consistency or thickness.
Rheology
A rotational viscometer is used to measure shear rate/shear stress of a drilling fluid - from which the Bingham Plastic parameters, PV and YP, are calculated directly. Other rheological models can be applied using the same data. The instrument is also used to measure thixotropic properties, gel strengths. The following procedure applies to a Fann Model 35, 6-speed VG Meter.
Plastic Viscosity (PV) and Yield Point (YP)
Step 1. Obtain a sample of the mud to be tested. Record place of sampling. Measurements should be made with minimum delay.
Step 2. Fill thermal cup approximately 2/3 full with mud sample. Place thermal cup on viscometer stand. Raise cup and stand until rotary sleeve is immersed to scribe lie on sleeve. Lock into place by turning locking mechanism (refer to Figure1).
Step 3. Place thermometer in thermal cup containing sample. Heat or cool sample to desired test temperature of 115× ±2×F.
Step 4. Flip VG meter toggle switch, located on right rear side of VG meter, to high position by pulling forward.
Step 5. Position red knob on top of VG meter to the 600-rpm speed. When the red knob is in the bot-tom position and the toggle switch is in the forward (high) position -this is the 600-rpm speed (refer to Figure2).
Step 6. With the sleeve rotating at 600-rpm, wait for dial reading in the top front window of VG meter to stabilize (minimum 10 seconds. Record 600-rpm dial reading.
Step 7. With red knob in bottom position, flip the VG meter toggle switch to low position by pushing the toggle switch away from you. Wait for dial reading to stabilize (minimum 10 seconds).
Record 300-rpm dial reading. [See Step8 to calculate the Plastic Viscosity and Yield Point].
Step 8. The Plastic Viscosity and Yield Point are calculated from the 600-rpm and 300-rpm dial read-ings as follows:
Gel Strength (10-sec/10-min)
Step 1. With red knob in bottom position, flip toggle switch to 600-rpm position (forward position). Stir mud sample for 10 seconds.
Step 2. Position red knob to the 3-rpm speed. When the red knob is in the middle position and the toggle switch is in low (rear) position - this is the 3-rpm speed. Flip toggle switch to off posi-tion. Allow mud to stand undisturbed for 10 seconds.
Rheological properties measured with a rotational viscometer are commonly used to indicate solids buildup, flocculation or deflocculation of solids, lifting and suspension capabilities, and to calculate hydraulics of a drilling fluid.
Step 3. After 10 seconds, flip toggle switch to low (rear) position and note the maximum dial reading.
This maximum dial deflection is the 10-second (initial) gel strength in lb/100 ft2. Record on the mud check sheet.
Step 4. Pull toggle switch to high and position red knob to 600-rpm speed. Stir mud for 10 seconds.
Step 5. After 10 seconds, and while mud is still stirring, position red knob to the 3-rpm speed. Flip toggle switch to off position and allow mud to stand undisturbed for 10 minutes.
Step 6. After 10 minutes, flip toggle switch to low (rear) position and note the maximum dial reading.
This maximum dial deflection is the 10-minute gel strength in lb/100 ft2. Record on the mud check sheet.
Static Filtration Tests
Static filtration tests are used to indicate filter cake quality and filtrate volume loss for a drilling mud under specific testing conditions. Filtration characteristics are affected by the types and quantities of solids and their physical and chemical interactions. Temperature and pressure further affect these solids and their interactions.
The following instructions for High-Pressure/High-Temperature Filtration will be applicable only to equipment used at DTC’s training lab. To operate any other units, manufacturer’s instructions should be carefully read before attempting to perform testing.
High-Temperature/High-Pressure Filtration (HTHP)
To operate this or any other unit, manufacturer’s instructions should be carefully read before attempting to perform testing. Extreme caution should be used in running this test. Equipment should be cleaned and maintained in good working condition (refer to Figure5).
Step 1. Plug heating jacket cord into correct voltage for the unit.
Step 2. Place metal thermometer in hole on outside from of heating jacket. Adjust thermostat and preheat jacket to 10×F above desired test temperature.
Step 3. While jacket is heating, check o-rings (3) on the following components and replace if worn or distorted:
Step 4. High-Pressure Regulator Step 5. Lid/Valve
Step 6. Cell Body
Step 7. (Refer to Figures6, 7, and 8 for details.)
Step 8. Stir mud sample 10 minutes with a high-speed mixer.
Step 9. Close Valve A by turning black knob clockwise.
Control of filtration properties of a drilling fluid can be useful in reducing tight hole conditions and fluid loss to formations.
Step 10. Turn handle counterclockwise on high pressure regulator, then load CO2 cartridge into cham-ber (refer to Figure6).
Step 11. Close valve B and pour stirred mud sample into cell, leaving 1/2 in. from the top lip to allow for expansion. Position o-ring in groove inside cell body. Place filter paper on top of o-ring (refer to Figure7).
Step 12. Open valve C and seat lid/valve assembly. Lubricate threads of allen screws with silicone grease and tighten (refer to Figure8).
Step 13. Close valve C low-pressure shut-off valve.
Step 14. Invert cell. (The lid/valve assembly is now at the bottom.) Carefully, install cell assembly into heating jacket.
Step 15. Transfer thermometer from the jacket to the thermometer well located on top of HTHP cell body (refer to Figure9).
Step 16. Slip high-pressure regulator (0-1500 psi) onto top of valve B and lock into place with steel ring.
Step 17. Slip low-pressure regulator (0-200 psi) on bottom of valve C. Lock into place with steel ring.
Be sure bleeder valve on low-pressure regulator is in the horizontal (closed) position.
Step 18. With valves B and C closed, apply 100 psi to both the high-pressure regulator and the low-pressure regulator by turning regulator handles clockwise.
Step 19. Open valve B. This is done to maintain 100 psi back pressure in the cell body while heating to the desired temperature. Heating time should not exceed 1 hour (refer to Figure10).
Step 20. When desired temperature is reached, increase pressure on high-pressure regulator to 600 psi by turning regulator handle clockwise.
Step 21. Open valve C. Start timer immediately at this point! Collect filtrate for 30 minutes, maintaining test temperature within ±5×F (refer to Figure11).
Step 22. At the end of 30 minutes close valve C. Carefully open valve D and collect filtrate. Leave valve open until low-pressure gauge reads 0 psi.
Step 23. Note the total volume of filtrate, test temperature and pressure, and cell heat-up time.
Because most HTHP filter presses have a filter area of 3.5 in.2, the filtrate volume collected must be doubled to correct to API standard 7.1 in.2 Calculate and record the API HTHP fil-trate as follows: API HTHP Filfil-trate = (2) (cm3 filtrate collected).
Caution: The Heating Jacket is hot!
Note: If pressure on low-pressure regulator rises above 100 psi during the test, cautiously reduce pressure by drawing off a portion of filtrate using valve D located on bottom of filtrate collec-tion chamber.
Step 24. Unplug unit and allow cell and contents to cool to room temperature before proceeding to dis-assembly procedure.
Step 25. After HTHP cell assembly and contents are cooled to room temperature, proceed with disas-sembly and cleaning procedure. Valves B and C should already be in the closed positions (refer to Figure12).
Step 26. To bleed pressure from the high-pressure (top) regulator, be sure Valve B is closed. Turn reg-ulator handle clockwise and carefully open Valve A. Bleed pressure until CO2 cartridge is expended and high-pressure gauge reads 0 psi (refer to Figure13).
Step 27. To bleed pressure from the low-pressure (bottom) regulator, be sure that valve C is closed.
Turn regulator handle clockwise and carefully open valve D. Bleed pressure until CO2 car-tridge is expended and low-pressure gauge reads 0 psi (refer to Figure 14). The pressure on the high-pressure gauge and the low-pressure gauge should now read 0 psi. If not, carefully bleed pressure until both gauges read 0 psi, then remove regulators.
Step 28. Remove cell from heating jacket and place in sink. Carefully open valve C and bleed pres-sure trapped in the cell. Now, open valve B. All prespres-sure should now be released (refer to Figure14).
Step 29. Remove Allen Screws, being careful to point the top assembly away from your body in case any pressure may be trapped (refer to Figure15).
Step 30. Open cell and carefully remove filter paper and cake from screen, being careful not to disturb the filter cake. Wash excess mud from cake with a small, gentle stream of base oil.
Step 31. Measure and report thickness of filter cake to nearest 1/32 of an inch. Describe condition of the cake.
Step 32. Discard the mud. Clean the cell. Cleaning includes removal of Valves B and C to prevent mud from drying in the cell assembly, which could cause valves to plug in future tests.