The ES test utilizes a probe with a pair of electrodes which are placed in the oil mud. A voltage is applied until the mud conducts a current. The ES value is indicated by a light on the instrument.
This test procedure is for the Fann Model 23C. The 23C will be replaced by the automated, sine-wave Fann 23D model (see Figure29).
Step 1. Place sample which has been screened through a Marsh funnel into a thermal cup. Hand stir with ES probe for 30 seconds.
Step 2. Heat sample to 120 ±5×F and record the temperature on the Drilling Mud Report.
Step 3. Set ES meter dial to zero. Immerse probe into mud sample. Ensure that the probe does not touch the sides or bottom of the thermal cup.
Step 4. Depress the red power button and hold it down during entire test. DO NOT MOVE probe dur-ing measurement.
Step 5. Starting from a zero reading, gradually increase the voltage by turning the knob clockwise at a rate of 100-200 volts per second until red indicator light illuminates. Note dial reading.
Return dial to zero. Wipe probe and thoroughly clean between the electrode plates with a paper towel. Repeat test to determine accuracy ±5% variation is satisfactory.
VEDTA cm3 of 0.1M EDTA cm3 of Mud
---=
CaOM, mg/L = (VED TA)(4000)
The relative stability of a water-in-oil emulsion mud is indicated by the breakdown voltage at which the emulsion becomes conductive.
Note:DO NOT USE detergent solutions or aromatic solvents such as xylene to clean the probe or cable.
Step 6. Electrical stability (ES) in volts is calculated as follows:
ES, volts = (2) (Dial Reading)
Sulfide
The oil mud sample to analyzed for sulfides is the whole mud, and not the filtrate. The sulfides of interest - that can be dangerous - are the sulfides that result from H2S reactions with lime plus any unreacted H2S. Therefore, it is necessary to analyze both liquid and solid phases of an oil mud. In the GGT a weak acid, citric acid (2M) with pH1.8, is used to avoid generating spurious sulfides from certain metal sulfide minerals. Sulfuric acid should not be used for this test as it is a strong acid and will liberate H2S from accessory minerals in barite.
Step 1. Be sure the Garrett Gas Train is clean and dry. Position gas train on magnetic stirrer so that it is level. (Remove rubber feet off GGT base.) Remove the top of the gas train and insert a teflon-coated magnetic stir bar to Chamber 1.
Step 2. Arrange the magnetic stirrer and gas train body so that the stir bar will rotate freely and vigor-ously agitate the contents of Chamber 1.
Figure 29 Electrical Stability Meter
When hydrogen sulfide gas (H2S) enters an oil mud it ionizes and slowly reacts with excess lime to form calcium sulfide salts. These active sulfides are able to revert to H2S gas, if the oil mud is contaminated by acidic water flow or by a high CO2 influx. Free H2S gas, even in low concentration, or active sulfide salts in high concentration present both a health and safety hazard on the rig. Therefore, monitoring active sulfides in an oil mud is critical, especially when drilling in known high H2S areas. Active sulfides can be quantitatively determined in a whole mud sample, not a filtrate, using a modified GGT test.
Step 3. With the gas regulator backed off, install and puncture a CO2 cartridge. (Bottled nitrogen (N2) or helium (He) is preferred.)
Step 4. Arrange the plastic injection tube through the rubber septum located on the top of Chamber 1 to allow the mud sample to be slowly injected to the bottom of Chamber 1 with a hypodermic syringe.
Step 5. Add 20 cm3 of 2M citric acid solution containing the demulsifier. (See note below to prepare citric acid solution.)
Step 6. Add 10 drops of octanol* to the contents of Chamber 1. (*Avoid inhalation or skin contact.) Figure 30
Garret Gas Train
Note:CAUTION — DO NOT use air or nitrous oxide (N2O) as a carrier gas.
Note:Citric Acid Solution (2 molar) containing Dowell Fluid Services Oil-Mud Demulsifier is pre-pared by dissolving 420 g reagent-grade citric acid, (C6H8O7. H2O) into 1000 cm3 de-ionized water. To this citric acid solution, add 200 cm3 of isopropanol and 25 cm3 of Dowell Oil-mud Demulsifier W35.
Step 7. Select the correct Dräger tube and sample volume required for the expected sulfide range (See Table 9).
Step 8. Break the tip off each end of the Dräger tube. Place the Dräger tube with the arrow pointing downward into the bored receptacle. Install flowmeter tube with the word, Top, in the upward position in Chamber 3. Make sure o-rings seal properly (Figure31).
Step 9. Install the top on the gas train, and hand tighten all screws evenly to seal the o-rings.
Step 10. With the regulator backed off (turn regulator handle counter-clockwise), connect the carrier gas to the dispersion tube of Chamber 1 using latex rubber or flexible inert plastic tubing. Do not clamp tubing. Connect the flexible tubing from Chamber 3 outlet to the Dräger tube.
Step 11. Adjust the dispersion tube in Chamber 1 to clear the stir-bar. Allow clearance of approxi-mately 1/4 in. off the bottom by loosening the white adjustment sleeve.
Step 12. To purge air from the GGT, gently flow carrier gas for 30 seconds by turning handle on regu-lator clockwise. Check for leaks. Shut off carrier gas by turning reguregu-lator handle counter-clockwise.
Step 13. With contents of Chamber 1 rapidly stirring, slowly inject a measured volume of oil mud through the injection tube using a hypodermic syringe. Keep the injection tube sealed with the syringe during the test. A rubber band can be used to hold the syringe plunger in place.
Stir at least 5 minutes or until the sample is well dispersed with no obvious oil drops.
Table 11.
Dräger Tube Identification Sample Volumes and Tube Factors to be Used for Various Sulfide Ranges Sulfide
*Tube Factor 600 is based on a Batch Factor (stenciled on box) of 0.40. For another Batch Factor (as stenciled on box), a corrected Tube Factor should be calculated:
Correct Tube Factor 600 Batch Factor ---0.40
=
Step 14. Immediately restart the carrier gas flow by turning the regulator handle clockwise. Adjust the rate between 200 to 400 ml/min (keep the flowmeter ball between the red lines on the flow-meter). Continue flowing for a total of 15 minutes.
Step 15. Observe changes in the appearance of the Dräger tube. Note and record the maximum dark-ened length (in units marked on the tube) before the stain front starts to smear. Continue the gas flow for a total of at least 15 minutes. With prolonged flow, the stain front may appear as a diffuse, feathery coloration. In the high-range tube, an orange color may appear ahead of the black front if sulfites, SO2=, are present in the sample. This orange region should be ignored. Record only the darkened length.
Step 16. Using the measured Sample Volume, the Dräger tube’s maximum Darkened Length, and the Tube Factor from Table 9, calculate the active sulfides as H2S in the sample as follows:
Step 17.
Step 18. * In units marked on the tube.
Step 19. To clean the gas train, remove the flexible tubing and remove the top. Take the Dräger tube and flowmeter out of the receptacles and plug the holes with stoppers to keep them dry.
Clean the chambers with warm water and a mild detergent, using a soft brush. Use a pipe cleaner to clean the passages between chambers. Wash the dispersion tube and the injec-tion tube with mineral oil, and then blow out the tube with air of CO2 gas. Rinse the unit with deionized water, and allow it to drain dry. If the dispersion tube frit plugs with solids, such as
Figure 31
Flowmeter and Dräger Tube Installed in GGT Base
Note:One CO2 cartridge should provide about 15 to 20 minutes of flow at this rate.
H2S, mg/L (Darkened Length*)(Tube Factor) Sample Volume, cm3
( )
---=
CaCO3 which forms from using CO2 carrier gas, soak the dispersion tube frit in strong acid;
rinse thoroughly, and blow it dry with gas.