API R ECOMMENDED P RACTICE 13B-1/ISO 10414-1 3 cCaSO4,A concentration of calcium sulfate, in kilograms per cubic metre cCaSO4,B concentration of calcium sulfate, in pounds per barrel USC
Symbols
NOTE Subscript “A” to symbol denotes metric units Subscript “B” to symbol denotes U.S customary units
The A B area measures in square inches, while the concentration of weighting material is specified in kilograms per cubic meter and pounds per barrel Additionally, the concentration of calcium ions is expressed in milligrams per liter, and the total hardness, represented by the combined concentration of calcium and magnesium ions, is also measured in milligrams per liter.
The API Recommended Practice 13B-1/ISO 10414-1 outlines various concentrations relevant to drilling fluids It specifies the concentration of calcium sulfate (c CaSO4) in both kilograms per cubic metre and pounds per barrel (USC), as well as the total soluble carbonates (c CO2+CO3+HCO3) measured in milligrams per litre Additionally, it details the concentration of chloride ions (c Cl) and excess undissolved calcium sulfate (c ex-CaSO4) in both metric and imperial units The document also addresses potassium chloride concentrations (c f,KCl and c KCl) in filtrate and drilling fluid, respectively, along with potassium ion (c K) and magnesium ion (c Mg) concentrations Sodium chloride concentrations (c NaCl) are provided in milligrams per litre and parts per million by mass Furthermore, it includes the concentration of sulphide ions (c S), suspended solids (c SS), and the methylene blue capacity (c MBT), along with a thermometer correction (c th) to adjust the working thermometer reading.
E BE,A bentonite equivalent, expressed in kilograms per cubic metre
E BE,B bentonite equivalent, expressed in pounds per barrel f tube factor from either Table A.1 or Table A.2, for sulfide or carbonate
F W fraction (volume fraction) of water k cor correction factor
The K cell constant is measured in square meters per meter, while the submerged lengths of the shear tube are represented as \( l_A \) in centimeters and \( l_B \) in inches The stain length of the Dräger tube is denoted as \( l_{st} \) The mass of the dried sample is indicated as \( m_{ds} \) in grams, and the mass of methylene blue is represented as \( m_s \) in grams Additionally, the mass of the shear tube is \( m_{st} \) in grams, and the total shear mass, which includes the platform and weights, is denoted as \( m_{tot} \) in grams The mass of water is indicated as \( m_W \) in grams, and the mass loss is measured in milligrams.
M f methyl orange alkalinity of the filtrate
P df phenolphthalein alkalinity of the drilling fluid
The phenolphthalein alkalinity of the filtrate (P f) is a crucial parameter in assessing the corrosion rate (q A) measured in kilograms per square meter per year and (q B) in pounds per square foot per year Additionally, the resistivity of the drilling fluid (r df) is expressed in ohm meters, while the filtrate resistivity (r f) is also measured in ohm meters, both of which are essential for understanding the fluid's properties and its impact on corrosion.
R QAS/STPB ratio of the concentration of QAS to that of STPB
R r resistivity meter reading, in ohms
R 1 average reading for the standard thermometer
R 2 average reading for the working thermometer
R 2,cor corrected reading for the working thermometer
R 300 viscometer dial reading at 300 r/min
R 600 viscometer dial reading at 600 r/min t exposure time, in hours t 1 initial reading taken at 7,5 min
API R ECOMMENDED P RACTICE 13B-1/ISO 10414-1 5 t 2 final reading taken at 30 min
V df volume of drilling fluid sample, in millilitres
V EDTA volume of EDTA solution, in millilitres
V EDTA,df EDTA volume of whole drilling fluid, in millilitres
V EDTA,f EDTA volume of the drilling fluid filtrate, in millilitres
V f volume of the filtrate, in millilitres
V mb volume of methylene blue solution, in millilitres
V o volume of oil, in millilitres
V PPT PPT volume, in millilitres
V RC retort cup volume, expressed in millilitres
V s volume of the sample, in millilitres
V sn volume of silver nitrate solution, in millilitres
V W volume of water, in millilitres
V 7,5 filtrate volume after 7,5 min, in millilitres
V 30 filtrate volume after 30 min, in millilitres v sf static filtration rate (velocity of flow), millilitres per square root of the minutes, in millilitres per minute
Y P,B yield point, in pounds per one hundred square feet
A shear strength, expressed in pascals
B shear strength, expressed in pounds per hundred square feet
DFG,A drilling fluid gradient, expressed in pascals per metre
The DFG,B drilling fluid gradient is measured in pounds per square inch per foot, while the apparent viscosity and plastic viscosity are expressed in millipascal seconds Additionally, temperature and density are important factors, with density being represented in grams per milliliter when compared to distilled water.
A density, expressed in kilograms per cubic metre
B1 density, expressed in pounds per gallon
B2 density is measured in pounds per cubic foot, while the density of weighting material is expressed in grams per millilitre The drilling fluid density is also given in grams per millilitre, as is the density of filtrate For low-gravity solids, use a density of 2.6 grams per millilitre if the value is unknown Additionally, the density of oil is typically 0.8 grams per millilitre when the exact measurement is not available.
The density of water, measured in grams per milliliter, is influenced by the test temperature Additionally, the volume fraction of weighting material is expressed as a percentage, along with the volume fraction of low-gravity solids and the volume fraction of oil, both also represented in percent.
S volume fraction of retort solids, in percent
SS volume fraction of suspended solids, in percent
W volume fraction of water, in percent
Abbreviations
ASTM American Society for Testing and Materials
HTHP high-temperature, high-pressure
MBT methylene blue test/capacity meq milliequivalents
OCMA Oil Companies Materials Association (originally, Middle East companies) PPA permeability plugging apparatus
PV plastic viscosity, in common oilfield terminology
USC U.S Customary units, commonly used in U.S.-based testing
4 Drilling fluid density (mud weight)
Principle
This test procedure determines the mass of a specific volume of liquid, which is equivalent to its density The density of drilling fluid is measured in grams per millilitre or kilograms per cubic metre, as well as in pounds per gallon or pounds per cubic foot.
Apparatus
4.2.1 Density-measuring instrument, of accuracy to within 0,01 g/ml or 10 kg/m 3 (0,1 lb/gal or 0,5 lb/ft 3 ).
The mud balance is a key instrument for determining drilling-fluid density, featuring a design where a drilling-fluid holding cup balances against a fixed counterweight A sliding-weight rider moves along a graduated scale for precise measurements, while a level-bubble ensures accurate balancing Optional attachments can extend the balance's range when needed.
The instrument should be calibrated frequently with fresh water Fresh water should give a reading of 1,00 g/ml or
The density of the substance is 1,000 kg/m³ (8.33 lb/gal or 62.3 lb/ft³) at a temperature of 21 °C (70 °F) If the density does not meet this standard, it is necessary to adjust the balancing screw or modify the quantity of lead shot in the well at the end of the graduated arm accordingly.
4.2.2 Thermometer, with a range of 0 °C to 105 °C (32 °F to 220 °F).
Procedure
4.3.1 The instrument base should be set on a flat, level surface
4.3.2 Measure and record the temperature of the drilling fluid
To test the drilling fluid, fill a clean, dry cup with the fluid and securely attach the cap, ensuring that some fluid is expelled through the cap's hole to eliminate any trapped air or gas For detailed instructions on air or gas removal, refer to Annex D.
4.3.4 Holding the cap firmly on the drilling-fluid holding cup (with cap hole covered), wash or wipe the outside of the cup clean and dry
4.3.5 Place the beam on the base support and balance it by moving the rider along the graduated scale Balance is achieved when the bubble is under the centreline
To determine the drilling fluid density, refer to one of the four calibrated scales located on the arrow side of the sliding weight The density is displayed in various units, including g/ml, lb/gal, and lb/ft³, or as a drilling fluid gradient measured in psi per 1,000 ft.
Calculation
4.4.1 Report the drilling fluid density to the nearest 0,01 g/ml or 10 kg/m 3 (0,1 lb/gal or 0,5 lb/ft 3 )
4.4.2 Equations (1) to (3) are used to convert the density, , expressed in grams per millilitre to other units:
A 1 000 (1) where A is the density, expressed in kilograms per cubic metre
B1 8,33 (2) where B1 is the density, expressed in pounds per gallon
B2 62,3 (3) where B2 is the density, expressed in pounds per cubic foot
Table 2 is provides the multiplication factor for conversion from one density unit to another
Equations (4) to (7) are used to convert the density to the drilling fluid gradient, DFG , expressed in pascals per metre (pounds per square inch per foot):
DFG,A is the drilling fluid gradient, expressed in pascals per metre;
DFG,B is the drilling fluid gradient, expressed in pounds per square inch per foot
A list of density conversions is given in Table 1
Pounds per cubic foot g/ml kg/m 3 (lb/US gal) (lb/ft 3 )
Pounds per cubic foot g/ml kg/m 3 (lb/US gal) (lb/ft 3 )
2,90 2 900 24,2 180,7 a Same value as relative density b Accurate conversion factor
Table 2 — Conversion of density units
Multiply to get g/ml kg/m 3 lb/gal lb/ft 3 g/ml 1 1 000 8,33 62,3 kg/m 3 0,001 1 0,008 3 16,026 lb/gal 0,120 120 1 7,49 lb/ft 3 0,016 0 16,03 0,133 5 1
5 Alternative drilling fluid density method
Principle
The density of drilling fluid with entrained air or gas can be more accurately measured using a pressurized mud balance This device operates similarly to a conventional mud balance, but it allows the slurry sample to be contained in a fixed-volume cup under pressure.
Pressurizing the sample cup is essential for reducing the impact of entrained air or gas on slurry density measurements This process minimizes the volume of any entrained air or gas, resulting in slurry density readings that more accurately reflect the conditions encountered downhole.
Apparatus
5.2.1 Density-measuring instrument, of accuracy to within 0,01 g/ml or 10 kg/m 3 (0,1 lb/gal or 0,5 lb/ft 3 )
The pressurized mud balance is a key instrument for determining the density of pressurized drilling fluids It features a design where a drilling-fluid holding cup and screw-on lid are balanced by a fixed counterweight, while a sliding-weight rider moves along a graduated scale For precise measurements, a level-bubble is incorporated into the beam to ensure accurate balancing.
Calibrate the instrument frequently with fresh water Fresh water should give a reading of 1,00 g/ml or
The density of the substance is 1,000 kg/m³ (8.33 lb/gal or 62.3 lb/ft³) at a temperature of 21 °C (70 °F) If the density does not meet this standard, it is necessary to adjust the balancing screw or modify the quantity of lead shot in the well at the end of the graduated arm accordingly.
5.2.2 Thermometer, with a range of 0 °C to 105 °C (32 °F to 220 °F).
Procedure
5.3.1 Measure and record the temperature of the drilling fluid
5.3.2 Fill the sample cup to a level slightly below the upper edge of the cup [approximately 6,5 mm (0,25 in)]
To properly seal the cup, position the lid with the check-valve in the open position and press it down until it makes contact with the cup's edge, allowing excess slurry to escape through the valve Once the lid is secured, pull the check-valve to the closed position, rinse the cup and threads with water, and then screw on the threaded cap.
The pressurizing plunger operates like a syringe, where it is filled by submerging its end in the slurry with the piston rod fully inserted By pulling the piston rod upward, the cylinder fills with slurry, which must then be expelled to avoid dilution from any residual liquid left over from previous clean-ups After expelling, the plunger should be refilled with a fresh slurry sample.
To properly pressurize the sample cup, apply downward force on the cylinder housing to keep the check-valve open while simultaneously pushing the piston rod inward It is essential to maintain a force of at least 225 N (50 lbf) on the piston rod during this process.
The pressure-actuated check-valve in the lid closes when the cup is pressurized, pushing the valve upward To properly close the valve, gradually reduce pressure on the cylinder housing while keeping pressure on the piston rod Once the check-valve is closed, release the pressure on the piston rod before disconnecting the plunger.
To weigh the pressurized slurry sample, first rinse and dry the exterior of the cup Position the instrument on the knife edge and adjust the sliding weight until the beam is balanced, indicated by the bubble centering between the two black marks The density can then be read directly from one of the four calibrated scales on the arrow side of the sliding weight, with measurements available in g/ml, lb/gal, lb/ft³, or as a drilling fluid gradient in psi/1,000 ft.
5.3.8 To release the pressure inside the cup, reconnect the empty plunger assembly and push downward on the cylinder housing
5.3.9 Clean the cup and rinse thoroughly with water For best operation in water-based slurries, the valve should be greased frequently with waterproof grease.
Calculation
Report the drilling fluid density to the nearest 0,01 g/ml or 10 kg/m 3 (0,1 lb/gal or 0,5 lb/ft 3 )
For conversions, use the equations given in 4.4.2
Principle
Viscosity and gel strength are key measurements that assess the flow properties of drilling fluids To measure these properties, various instruments are utilized, including the Marsh funnel, which provides a straightforward indication of viscosity, and the direct-indicating viscometer, a mechanical device that measures viscosity at different shear rates For more detailed information on the rheology of drilling fluids, please refer to Reference [3].
Determination of viscosity using the Marsh funnel
6.2.1.1 Marsh funnel, calibrated to out-flow 946 ml (1 quart) of fresh water at a temperature of (21 3) °C
[(70 5) °F] in (26 0,5) s, with a graduated cup as a receiver
6.2.1.1.1 Funnel cone, of length 305 mm (12,0 in), diameter 152 mm (6,0 in) and a capacity to bottom of screen of 1 500 ml (1,6 quarts)
6.2.1.1.2 Orifice, of length 50,8 mm (2,0 in) and inside diameter 4,7 mm (0,188 in 3/16 in)
6.2.1.1.3 Screen, with 1,6 mm (0,063 in 1/16 in) openings (12 mesh); fixed at 19,0 mm (0,75 in ắ in) below top of funnel
6.2.1.2 Graduated cup, with capacity at least 946 ml (1 quart)
6.2.1.4 Thermometer, with a range of 0 °C to 105 °C (32 °F to 220 °F)
6.2.2.1 Cover the funnel orifice with a finger and pour freshly sampled drilling fluid through the screen into the clean, upright funnel Fill until fluid reaches the bottom of the screen
6.2.2.2 Remove finger and start stopwatch Measure the time for drilling fluid to fill to 946 ml (1 quart) mark of the cup
6.2.2.3 Measure temperature of the fluid, in degrees Celsius (degrees Fahrenheit)
6.2.2.4 Report the time (6.2.2.2), to the nearest second, as the Marsh funnel viscosity Report the temperature (6.2.2.3) of fluid to the nearest degree Celsius (degree Fahrenheit).
Determination of viscosity and/or gel strength using a direct-indicating viscometer
A rotational viscometer, operated by an electric motor or hand crank, measures the viscosity of drilling fluid contained between two concentric cylinders The outer rotor sleeve rotates at a constant speed, generating torque on the inner bob, which is restrained by a torsion spring A dial connected to the bob displays its displacement The instrument is calibrated to determine plastic viscosity and yield point using readings taken at rotor sleeve speeds of 300 r/min and 600 r/min.
A direct-indicating viscometer must adhere to specific specifications, including a rotor sleeve with an inside diameter of 36.83 mm (1.450 in) and a total length of 87.0 mm (3.425 in) The sleeve features a scribed line positioned 58.4 mm (2.30 in) above the bottom, along with two rows of holes measuring 3.18 mm (0.125 in) that are spaced 120 degrees (2.09 radians) apart, located just below the scribed line Additionally, the bob should be closed, with a flat base and tapered top, having a diameter of 34.49 mm (1.358 in) and a cylinder length of 38.0 mm (1.496 in) Lastly, the viscometer's torsion spring constant is also a critical specification.
386 dyne-cm/degree deflection; d) rotor sleeve speed: high speed 600 r/min; low speed 300 r/min
NOTE Other rotor speeds are available in viscometers from various manufacturers
6.3.1.3 Thermometer, with a range of 0 °C to 105 °C (32 °F to 220 °F)
6.3.1.4 Suitable container, e.g., the cup provided with the viscometer
To ensure accurate measurements, place the sample in a container and immerse the rotor sleeve to the scribed line Conduct field measurements promptly, ideally within 5 minutes, and maintain a temperature close to that of the drilling fluid, with a maximum difference of 6 °C (10 °F) Additionally, the sampling location must be clearly indicated on the test report.
When testing fluids at temperatures exceeding 90 °C (200 °F), it is crucial to use a solid metal bob or a hollow metal bob that is completely dry inside This precaution is necessary because any liquid trapped within a hollow bob can vaporize in high-temperature fluids, potentially leading to an explosion.
6.3.2.2 Record the temperature of the sample
At a sleeve rotation speed of 600 r/min, allow the viscometer dial to stabilize, which may vary based on the characteristics of the drilling fluid Once steady, record the dial reading for the 600 r/min measurement.
6.3.2.4 Reduce the rotor speed to 300 r/min and wait for the viscometer dial reading to reach a steady value Record the dial reading for 300 r/min
6.3.2.5 Stir drilling fluid sample for 10 s at 600 r/min Stop the rotor
To determine the initial gel strength of the drilling fluid, allow the sample to stand undisturbed for 10 seconds Then, gradually turn the hand-wheel in the correct direction to achieve a positive dial reading For instruments operating at a speed of 3 r/min, the highest reading obtained after initiating rotation at this speed represents the initial gel strength Record this value, expressed in pounds per 100 ft², as the 10-second gel strength.
The gel strength value obtained from the dial reading is an approximation measured in lbf/100•ft² The dial readings indicate degrees of deflection, where each degree corresponds to 0.511 Pa in SI units and 1.067 lbf/100•ft² in USC units For ease of reporting, these precise unit conversions are frequently overlooked, and it is common practice in the field to simplify the reporting of pascals by dividing the dial units by 2.
1 r/min of the rotor equals a shear rate of 1.7023 s -1
Re-stir the drilling fluid sample at 600 r/min for 10 seconds, then stop the rotor and let the fluid sit undisturbed for 10 minutes After this period, repeat the measurements as outlined in section 6.3.2.6 and report the highest reading as the 10-minute gel strength in pounds per 100 ft².
The gel strength value obtained from the dial reading is an approximation measured in lbf/100•ft² The dial reading reflects degrees of deflection, where each degree corresponds to 0.511 Pa in SI units and 1.067 lbf/100•ft² in USC units For ease of reporting, these precise unit conversions are frequently overlooked, and a common practice in the field is to simplify the reporting of pascals by dividing the dial units by 2.
1 r/min of the rotor equals a shear rate of 1.7023 s -1
The calculation for the plastic viscosity, ηP, expressed in millipascal seconds (centipoise), is given in Equation (8):
R 600 is the dial reading at 600 r/min;
R 300 is the dial reading at 300 r/min
NOTE 1 The plastic viscosity is commonly known in the industry by the abbreviation PV
The calculation for the yield point, Y P,A , expressed in pascals, is given in Equation (9):
When calculating values in USC units, the yield point (expressed in pounds per one hundred square feet) is calculated as follows:
NOTE 3 The yield point, expressed in pounds per one hundred square feet, is commonly known in the industry by the abbreviation YP
The calculation for apparent viscosity, ηa , expressed in millipascal seconds (centipoise), is given in Equation (11): a 600 2 η = R (11)
NOTE 4 The apparent viscosity, expressed in millipascal seconds (centipoise), is commonly known in the industry by the abbreviation AV
Principle
The measurement of filtration behavior and filter cake-building characteristics in drilling fluids is essential for effective control and treatment Key factors include the filtrate's oil, water, or emulsion content, which are influenced by the types and quantities of solids present, as well as their physical and chemical interactions These interactions are further affected by variations in temperature and pressure, necessitating tests at both low pressure/low temperature and high pressure/high temperature, each requiring specialized equipment and techniques.
Low-temperature/low-pressure test
7.2.1.1 Filter press, consisting mainly of a cylindrical drilling-fluid cell having an inside diameter of 76,2 mm
(3 in) and a height of at least 64,0 mm (2,5 in)
The cell is constructed from materials that withstand strong alkaline solutions and is designed for easy admission and removal of a pressure medium from the top It accommodates a 90 mm (3.54 in) diameter filter paper placed above a suitable support, providing a filtration area of (45.8 ± 0.6) cm² [(7.1 ± 0.1) in²] A drain tube is located below the support to discharge the filtrate into a graduated cylinder, with sealing achieved through gaskets and the entire assembly supported by a stand Pressure can be applied using any non-hazardous fluid medium, and presses come equipped with pressure regulators, available with portable pressure cylinders, midget pressure cartridges, or hydraulic pressure options For consistent results, a single thickness of the appropriate 90 mm diameter filter paper, such as Whatman No 50 or S&S No., should be used.
576 1) or equivalent) shall be used.
The low-temperature/low-pressure filter press requires a filter area ranging from 45.2 cm² to 46.4 cm² (7.0 in² to 7.2 in²), corresponding to a diameter between 75.86 mm and 76.86 mm (2.987 in to 3.026 in) The filter press gasket is crucial in determining the filter area, and it is advisable to test the gasket using a conical gauge marked with maximum and minimum diameters of 76.86 mm (3.026 in) and 75.86 mm (2.987 in), respectively Any gasket that falls outside these specified dimensions should be discarded.
NOTE Results obtained from the use of a filter press with different filter area do not directly correlate with the results obtained when using the standard-sized press
7.2.1.2 Timer, with at least a 30 min interval
7.2.1.3 Graduated cylinder, with a volume of 10 ml (TC) or 25 ml (TC)
Ensure that all components of the cell, especially the screen, are clean and dry, and check that the gaskets are not distorted or worn Pour the drilling fluid sample into the cell, filling it to within 1 to 1.5 cm (0.4 to 0.6 in) from the top to minimize CO₂ contamination of the filtrate, and then complete the assembly with the filter paper in position.
To conduct the test, position a dry graduated cylinder beneath the drain tube to gather the filtrate Close the relief valve and adjust the regulator to achieve a pressure of 690 kPa (100 psi) within 30 seconds or less The testing period commences once the pressure is applied.
Whatman No 50 and S&S No 576 are commercially available products that are suitable for use, as mentioned in ISO 10414 However, it is important to note that this information is provided for user convenience and does not imply any endorsement by ISO or API for these specific products.
After 30 minutes, measure the volume of the collected filtrate Then, turn off the flow using the pressure regulator and cautiously open the relief valve If the time interval differs from 30 minutes, be sure to report it.
7.2.2.4 Report the volume of filtrate in millilitres (to the nearest 0,1 ml) and the initial drilling fluid temperature in degrees Celsius (degrees Fahrenheit) Save the filtrate for chemical analysis
To remove the cell from the frame, ensure that all pressure is relieved first Carefully save the filter paper while minimizing disturbance to the cake, then disassemble the cell and discard the drilling fluid Finally, wash the filter cake on the paper using a gentle stream of water.
7.2.2.6 Measure and report the thickness of the filter cake, to the nearest millimetre (1/32 in)
7.2.2.7 Although cake descriptions are subjective, such notations as hard, soft, tough, rubbery, firm, etc., can convey important information of cake quality.
High-temperature/high-pressure (HTHP) test
The HT/HP filter press is equipped with a controlled pressure source, such as CO₂ or nitrogen, and features regulators to manage working pressures ranging from 4,000 kPa to 8,900 kPa (600 psi to 1,300 psi) It includes a heating system for the drilling-fluid cell and a pressurized collection cell that maintains appropriate backpressure to prevent the flashing or evaporation of the filtrate Key components of the drilling-fluid cell consist of a thermometer well, oil-resistant gaskets, a support for the filter medium, and a valve on the filtrate delivery tube to regulate flow Regular replacement of the gaskets may be necessary to ensure optimal performance.
Safety features like an overheating safety fuse for the heating jacket and a pressure indicating device on the filtration cell enhance operational security Additionally, specialized devices are available to assist in cell disassembly when there are concerns about trapped pressures.
DANGER — Rigid adherence to manufacturers' recommendations as to sample volumes, equipment temperatures and pressures is essential Failure to do so can result in serious injury
Using nitrous oxide cartridges as pressure sources for HT/HP filtration is extremely dangerous, as they can detonate when exposed to grease, oil, or carbonaceous materials under temperature and pressure These cartridges should only be utilized for Garrett gas-train carbonate analysis.
7.3.1.2.1 Filter paper, Whatman No 50 or equivalent, for temperatures to 190 °C (375 °F)
7.3.1.2.2 Porous disc, Dynalloy X-5 or equivalent, for temperatures above 200 °C (400 °F) A new disc is required for each test
7.3.1.3 Timer, with at least a 30 min interval
7.3.1.4 Thermometer, with a range up to 260 °C (500 °F)
7.3.1.5 Graduated cylinder, with a volume of 25 ml (TC) or 50 ml (TC)
Whatman No 50 and Dynalloy X-5 discs are commercially available products, with Dynalloy being a trademark of Memtec America Corporation This information is provided for user convenience in relation to ISO 10414 and does not imply any endorsement by ISO/API of these products.
7.3.2.1 Place the thermometer in the well in the jacket and preheat to 6 °C (10 °F) above the desired temperature Adjust the thermostat to maintain the desired temperature
Stir the drilling fluid sample for 10 minutes using a high-speed mixer After mixing, close the valve on the drilling-fluid cell and carefully pour the sample into the cell, ensuring it is filled no closer than 1.5 cm (0.6 in) from the top to allow for expansion Finally, install the filter paper.
To complete the assembly of the cell, ensure both the top and bottom valves are closed before placing it in the heating jacket Additionally, transfer the thermometer to the well within the drilling fluid cell.
7.3.2.4 Connect the high-pressure collection cell to the bottom valve and lock in place
7.3.2.5 Connect a regulated pressure source to the top valve and collection cell, and lock in place
To conduct the pressure test, keep the valves closed and adjust the top and bottom regulators to 690 kPa (100 psi) Then, open the top valve to apply this pressure to the drilling fluid and maintain it for one hour If the temperature of the drilling fluid cell does not reach the specified test temperature within this time frame, the test must be stopped, and the equipment should be repaired.
A recent API-funded study revealed that certain equipment for high-temperature filtration testing fails to sufficiently heat drilling fluid to the required test temperature To address this issue, modifications can be implemented in the drilling-fluid cell by adding an internal heat sink and insulation Additionally, accurate temperature measurement during the heating phase can be achieved by installing a thermocouple to directly monitor the drilling fluid temperature within the cell.
After one hour, increase the top pressure unit to 4,140 kPa (600 psi) and open the bottom valve to initiate filtration Collect the filtrate for 30 minutes while keeping the temperature within 3 °C (5 °F) If the backpressure exceeds 690 kPa (100 psi) during the test, carefully reduce the pressure by drawing off some filtrate Ensure to record the total volume collected, along with the temperature, pressure, and time.
7.3.2.8 Correct the filtrate volume to a filter area of 45,8 cm 2 (7,1 in 2 ) For example, if the filter area is 22,6 cm 2 (3,5 in 2 ), double the filtrate volume reported
7.3.2.9 At the end of test, close top and bottom valves on the drilling fluid cell Bleed pressure from the regulators
DANGER: The drilling fluid cell maintains a pressure of approximately 4,140 kPa (600 psi) To prevent serious injury, ensure the cell is kept upright and at room temperature before bleeding off pressure prior to disassembly Difficulty in removing set screws may indicate residual pressure in the cell Consider using pressure-indicating devices for added safety, and utilize available tools designed to assist in disassembling cells when trapped pressures are suspected.
To safely remove the cell from the heating jacket, ensure that both the bottom and top valves are securely closed and that all pressure has been released from the regulators Carefully preserve the filter paper while placing the cell upright, then open the valve to release pressure from the cell contents Discard the drilling fluid and retrieve the filter cake, washing it gently with a stream of water on the paper.
7.3.2.11 Measure and report the thickness of the filter cake, to the nearest millimetre (1/32 in)
7.3.2.12 Although cake descriptions are subjective, such notations as hard, soft, tough, rubbery, firm, etc., can convey important information on cake quality
7.3.3.1 Place the thermometer in the well in the jacket and preheat to 6 °C (10 °F) above the desired temperature Adjust the thermostat to maintain the correct temperature
Stir the drilling fluid sample for 10 minutes using a high-speed mixer After mixing, close the valve on the drilling-fluid cell and carefully pour the sample into the cell, ensuring it is filled no closer than 4 cm (1.5 in) from the top to accommodate expansion Finally, install the appropriate filter medium as specified in section 7.3.1.2.
Not all equipment from manufacturers is suitable for use at temperatures exceeding 150 °C (300 °F), and ignorance of the pressure/temperature ratings can lead to severe injuries It is crucial to implement additional safety measures when conducting tests at high temperatures and pressures.
All pressure cells must include manual relief valves, while heating jackets should have an overheat safety fuse and a thermostatic cut-off for safety As test temperatures increase, the vapor pressure of the liquid phase in drilling fluids becomes a crucial design consideration Refer to Table 3 for water-vapor pressures at different temperatures.
To complete the assembly of the cell, ensure that both the top and bottom valves are closed before placing the drilling fluid cell into the heating jacket Next, transfer the thermometer into the well within the drilling fluid cell.
7.3.3.4 Connect the high-pressure collection cell to the bottom valve and lock in place
7.3.3.5 Connect the regulated pressure source to the top valve and the collection cell and lock in place
Principle
The retort instrument is essential for separating and measuring the volumes of water, oil, and solids in water-based drilling fluid samples By heating a known volume of the sample, the liquid components vaporize, condense, and are collected in a graduated receiver, allowing for direct measurement of liquid volumes The total volume of solids is calculated by subtracting the liquid volume from the total sample volume, while calculations for suspended solids are necessary as dissolved solids remain in the retort Additionally, the relative volumes of low-gravity solids and weighting material can be determined, making knowledge of solids concentration and composition crucial for effective viscosity and filtration control in water-based drilling fluids.
Apparatus
Retorts of three sizes (10 ml 20 ml and 50 ml) are commonly available Specifications for these retorts are given below
8.2.1.1 Sample cup, in a standard size of 10 ml (precision 0,05 ml), 20 ml (precision 0,10 ml) or 50 ml
NOTE Other sample cup sizes are available from manufacturers of this equipment
8.2.1.2 Liquid condenser, of sufficient mass to cool the oil and water vapours below their vaporization temperature prior to leaving the condenser
8.2.1.3 Heating element, of sufficient power to raise the temperature of the sample above the vaporization point of the liquid components within 15 min without causing solids boil-over
8.2.1.4 Temperature control (optional), capable of limiting the temperature of the retort to 500 °C 40 °C
8.2.2 Liquid receiver (TC), specially designed cylindrical glassware with a rounded bottom to facilitate cleaning and a funnel-shaped top to catch falling drops, meeting the following specifications:
Frequency of graduation marks (0 to 100 %), ml: 0,10 0,10 0,50
Calibration: To contain (TC) at 20 °C (68 °F)
Scale: ml or volume fraction (as percent)
Material: Transparent and inert to oil, water and salt solutions at temperatures up to 32 °C (90 °F)
The receiver volume should be verified gravimetrically The procedure and calculations are provided in Annex H for the 10 ml, 20 ml and 50 ml liquid receivers
8.2.3 Fine steel wool, oil-free
“Liquid steel wool” or similar products should not be used for this application
8.2.4 High-temperature silicone grease, to be used as a thread seal and a lubricant
8.2.6 Putty knife or spatula, with blade shaped to fit the inside dimensions of the sample cup of the retort 8.2.7 Marsh funnel
Procedure
Ensure that the retort sample cup, condenser passage, and liquid receiver are clean, dry, and cooled from previous use Thoroughly clean the inside of the sample cup and lid with a putty knife or spatula before each test, and periodically polish the interior with steel wool Additionally, clean and dry the condenser passage using pipe cleaners before each test, as any material build-up can reduce condensation efficiency and lead to inaccurate liquid readings.
NOTE Procedures vary slightly depending on type of retort used See manufacturers' instructions for complete procedure
8.3.2 Collect a representative sample of water-based drilling fluid and allow it to cool to approximately 27 °C
(80 °F) Screen the sample through the 1,68 mm (0,066 in) (12 mesh) screen on the Marsh funnel to remove lost- circulation material, large cuttings or debris
To effectively eliminate gas or air from a drilling fluid sample, add two to three drops of a defoaming agent to approximately 300 ml of the fluid Stir the mixture gently for 2 to 3 minutes to facilitate the release of gases.
To ensure optimal performance and ease of maintenance, apply a light layer of silicone grease to the threads of the sample cup and condenser tube This lubrication not only minimizes vapor loss through the threads but also simplifies the disassembly and cleaning process after the test is completed.
8.3.5 Lightly pack a ring of steel wool into the chamber above the sample cup Use only enough steel wool to prevent boil-over of solids into the liquid receiver
NOTE This is determined from experience
8.3.6 Fill the retort sample cup with degassed water-based drilling fluid, see 8.3.3 See Annex D for information on air or gas removal
To ensure the correct volume of the sample is in the cup, carefully place the lid on the sample cup, allowing for an overflow of the sample through the hole in the lid.
Ensure the lid is securely in place while wiping away any overflow from the sample cup and lid After cleaning, confirm that the threads of the sample cup remain coated with silicone grease and that the hole in the lid is unobstructed.
8.3.9 Screw the retort cup onto the retort chamber with its condenser
8.3.10 Place a clean, dry, liquid receiver under the condenser discharge tube
8.3.11 Heat the retort and observe the liquid falling from the condenser Continue heating for 10 min after the last condensate is collected
Remove the liquid receiver from the retort and check for any solids in the recovered liquid If solids are present, it indicates that the entire drilling fluid has boiled over from the sample cup, necessitating a repeat of the test starting from section 8.3.6.
8.3.13 Read the volumes of water and oil in the liquid receiver after it has cooled to ambient temperature Record the volumes (or volume percentages) of water and oil collected
8.3.14 Cool the retort, remove the steel wool with corkscrew and clean the sample cup with a putty knife or spatula.
Calculation
8.4.1 Using the measured volumes of oil and water and the volume of the original whole drilling fluid sample
(10 ml, 20 ml, or 50 ml), calculate as percentages the volume fractions of water, oil and total solids in the drilling fluid a) volume fraction water:
The volume fraction water, W , expressed as a percentage of the total sample volume, is calculated as given in Equation (12):
V W is the volume of water, expressed in millilitres;
V df is the volume of the drilling fluid sample, expressed in millilitres b) volume fraction oil:
The volume fraction oil, o , expressed as a percentage of the total sample volume, is calculated as given in Equation (13): o o df
V o is the volume of oil, expressed in millilitres;
V df is the volume of the drilling fluid sample, expressed in millilitres c) volume fraction retort solids:
The volume fraction retort solids, S , expressed as a percentage of the total sample volume, is calculated as given in Equation (14):
The percentage of retort solids, as indicated in Equation (14), is calculated by subtracting the combined volume of water and oil from the total sample volume (10 ml, 20 ml, or 50 ml) This calculation accounts for both suspended solids, including weighting materials and low-gravity substances, as well as dissolved materials such as salt It is important to note that this percentage represents only suspended solids when the drilling fluid is an untreated, fresh-water drilling fluid.
To determine the percentage of suspended solids (volume fraction) in drilling fluids, additional calculations are necessary, which also relate to the volumes of low-gravity solids and weighting materials Accurate measurements of drilling fluid density and chloride concentration are essential for these calculations The volume fraction of suspended solids, denoted as ϕSS, is expressed as a percentage of the total sample volume and can be calculated using Equation (15).
1 680 000 - 1,21 Cl c c ϕ =ϕ − ϕ × (15) where c Cl is the chloride concentration, in milligrams per litre; ϕW is the percentage (volume fraction) of water; ϕS is the percentage (volume fraction) of solids
The volume fraction of low-gravity solids, denoted as \$\phi_{lg}\$, is calculated as a percentage of the total sample volume This calculation is outlined in Equation (16) for SI units and Equation (17) for USC units.
The drilling fluid density, denoted as \$\rho_{df,A}\$ in grams per millilitre and \$\rho_{df,B}\$ in pounds per gallon, is calculated using the formula provided in Equation (17) The filtrate density, represented as \$\rho_f\$, is determined by Equation (18), which states that \$\rho_f = 1 + 0.00000109 \cdot c \cdot Cl\$ Additionally, the density of the weighting material is indicated as \$\rho_b\$ in grams per millilitre, while the density of low-gravity solids is represented as \$\rho_{lg}\$ in grams per millilitre, with a default value of 2.6 if unknown The density of oil, denoted as \$\rho_o\$, is expressed in grams per millilitre, using a default value of 0.8 if the actual density is unknown.
NOTE The ρf density calculation Equation (18) is based on the sodium chloride concentration
8.4.4 The volume fraction of the weighting material, ϕb, expressed as a percentage, is calculated as given in
The concentration of low-gravity solids (\$c_{lg,A}\$), weighting material (\$c_{b,A}\$), and suspended solids (\$c_{SS,A}\$) is expressed in kilograms per cubic metre and can be calculated using the following equations: \$$c_{lg,A} = 10\rho_{lg} \times \phi_{lg} \$$\$$c_{b,A} = 10\rho_{b} \times \phi_{b} \$$\$$c_{SS,A} = c_{lg,A} + c_{b,A} \$$In these equations, \$\phi_{lg}\$ represents the volume fraction of low-gravity solids, while \$\phi_{b}\$ denotes the volume fraction of barite, both expressed as percentages.
The concentration of low-gravity solids, weighting material, and suspended solids can be calculated in pounds per barrel using specific equations The concentration of low-gravity solids, denoted as \$c_{lg,B}\$, is given by Equation (23), while the concentration of weighting material, \$c_{b,B}\$, is defined in Equation (24) Additionally, the concentration of suspended solids, \$c_{SS,B}\$, is determined by Equation (25), which incorporates both \$c_{lg,B}\$ and \$c_{b,B}\$ Here, \$lg\$ represents the volume fraction of low-gravity solids as a percentage, and \$b\$ indicates the volume fraction of barite, also expressed as a percentage.
Principle
The sand content of drilling fluid is the percentage (volume fraction) of particles of diameter larger than 74 àm It is measured by a sand-sieve set.
Apparatus
9.2.1 Sieve, 74 àm (200 mesh) and 63,5 mm (2,5 in) in diameter
9.2.3 Glass measuring tube, marked for the volume of drilling fluid to be added and graduated from 0 % to
20 % in order to read the percentage of sand directly.
Procedure
9.3.1 Fill the glass measuring tube with drilling fluid to the “drilling fluid” mark Add water to the next mark Close the mouth of the tube and shake vigorously
Pour the mixture onto a clean, wet sieve and discard the liquid that passes through Add more water to the tube, shake it, and pour again onto the sieve Repeat this process until the tube is clean, then wash the sand retained on the sieve to remove any remaining drilling fluid.
To measure the volume percent of sand, place the funnel upside down over the sieve, then invert the assembly and insert the funnel's tip into the glass tube Gently wash the sand into the tube using a fine spray of water through the sieve, and allow the sand to settle Finally, read the volume percent of the sand from the graduations on the tube.
Report the sand content of the drilling fluid as a percentage (volume fraction) and specify the source of the sample, such as above the shaker or from the suction pit Additionally, note the presence of coarse solids other than sand, like lost circulation material, which are retained on the sieve.
Principle
The methylene blue capacity of drilling fluid indicates the presence of reactive clays, such as bentonite and drill solids, as measured by the methylene blue test This capacity serves as an estimate of the total cation-exchange capacity of the drilling fluid solids However, it is important to note that methylene blue capacity and cation-exchange capacity are not always equivalent, with the former typically being lower than the actual cation-exchange capacity.
Methylene blue solution is introduced to a treated sample of drilling fluid until a saturation point is reached, indicated by a dye "halo" around a drop of the solids suspension on filter paper This method can also be adapted for drill solids and commercial bentonite, enabling an estimation of the quantities of each solid type in the fluid, as referenced in ISO 10416 and API RP 13I.
Drilling fluids often include various substances alongside reactive clays that can absorb methylene blue To mitigate the influence of organic materials like lignosulfonates, lignites, cellulosic polymers, and polyacrylates, pretreatment with hydrogen peroxide is employed.
Reagents and apparatus
10.2.1 Methylene blue solution, reagent grade methylene blue (CAS No 61-73-4), 3,20 g/l (1 ml 0,01 meq)
The moisture content of reagent grade methylene blue must be determined each time the solution is prepared To do this, dry a 1,000 g sample of methylene blue at a constant temperature of 93 °C (200 °F) while allowing for a variation of 3 °C (5 °F) Subsequently, make the necessary correction to the mass of methylene blue, denoted as \( m_s \) in grams, to accurately prepare the solution as outlined in Equation (26).
, s ds m 3 2 m (26) where m ds is the mass of the dried sample, expressed in grams
10.2.2 Hydrogen peroxide (CAS No 7722-88-5), 3 % solution
DANGER — H 2 O 2 is a strong oxidizer Contact with skin should be avoided
10.2.3 Sulfuric acid (CAS No 7664-93-9), dilute, approximately 2,5 mol/l (5 N)
DANGER — H 2 SO 4 is a strong and toxic acid
10.2.4 Syringe, 2,5 ml (TD) or 3 ml (TD)
10.2.6 Burette, 10 ml (TD); micropipette, 0,5 ml (TD); or graduated pipette, 1 ml (TD)
10.2.10 Filter paper, Whatman No 1 3) or equivalent.
Procedure
To prepare the solution, add 2.0 ml of drilling fluid (or an appropriate volume ranging from 2 ml to 10 ml of methylene blue solution) to 10 ml of water in an Erlenmeyer flask, ensuring that the syringe used has a capacity greater than the required volume.
To accurately add 2.0 ml of drilling fluid, follow these steps: First, remove any air or gas from the drilling fluid by stirring it to break the gel, then quickly draw the fluid into the syringe while keeping the tip submerged Next, fill the syringe until the plunger reaches the last graduation mark (e.g., the 3-ml line on a 3-ml syringe) Finally, dispense 2.0 ml by pushing the plunger until it is positioned exactly at the 2 ml mark from the last graduation, which corresponds to the 1-ml line on a 3-ml syringe.
10.3.2 Add 15 ml of 3 % hydrogen peroxide and 0,5 ml of sulfuric acid Boil gently for 10 min, but do not allow to boil to dryness Dilute to about 50 ml with water
To conduct the titration, add the methylene blue solution to the flask in increments of 0.5 ml If prior tests indicate the approximate amount needed to reach the endpoint, larger increments of 1 ml to 2 ml can be used initially After each addition, swirl the flask for about 30 seconds While the solids remain suspended, use a stirring rod to remove a drop of liquid and place it on filter paper The initial endpoint is identified by the appearance of a blue or turquoise ring around the dyed solids, as illustrated in Figure 1, key item 5.
When the blue tint from the spot is observed, shake the flask for an additional 2 minutes and apply another drop on the filter paper If a blue ring appears again, the final endpoint is reached, as indicated in key item 7 (7 ml) in Figure 1 Free dye is initially detected after adding the sixth millilitre, but it is adsorbed after two minutes, showing that the endpoint has not yet been reached However, after adding the seventh millilitre, free dye is detected again and remains unadsorbed after two minutes, confirming that this is the endpoint.
Whatman No 1 is a commercially available product that serves as a suitable example for users of ISO 10414 However, it is important to note that this mention does not imply any endorsement by ISO or API for these products.
1 volume of methylene blue solution added
2 no free, unadsorbed dye present
3 drilling fluid solids, dyed blue
7 endpoint retest after 2 min reaction
Figure 1 — Spot tests for endpoint of methylene blue titration
Calculation
Report the methylene blue capacity, c MBT , of the drilling fluid, calculated as follows:
V mb is the volume of methylene blue solution, expressed in millilitres;
V df is the volume of drilling fluid sample, expressed in millilitres
The methylene blue capacity can be expressed as bentonite equivalent, denoted as E BE,A in kilograms per cubic meter, based on bentonite with a cation exchange capacity of 70 meq/100 g Alternatively, it can be reported as E BE,B in pounds per barrel.
The kilograms per cubic metre (or pounds per barrel) of bentonite equivalent derived from Equations (28) and (29) does not represent the total amount of commercial bentonite in the drilling fluid This measurement also includes contributions from reactive clays found in the drill solids For further details on estimating the quantities of commercial bentonite and drill solids, refer to ISO 10416 [4] or API RP 13I [5].
Principle
Field measurement and adjustment of drilling fluid pH are essential for effective drilling fluid control The pH level influences clay interactions, the solubility of various components and contaminants, and the performance of additives Additionally, maintaining the appropriate pH is crucial for managing acidic and sulfide-corrosion processes.
The term "pH" refers to the negative logarithm of hydrogen ion activity in aqueous solutions, expressed as pH = -log [H⁺] At 24 °C (75 °F), pure water has a hydrogen ion activity of [H⁺] = 10⁻⁷ mol/l, resulting in a pH of 7, which is considered neutral since the hydroxyl ion activity [OH⁻] is also 10⁻⁷ mol/l The ion product of water at this temperature is [H⁺][OH⁻] = 10⁻¹⁴, indicating that an increase in hydrogen ion concentration corresponds to a decrease in hydroxyl ion concentration A change in pH by one unit signifies a ten-fold change in both [H⁺] and [OH⁻] Solutions with a pH less than 7 are classified as acidic, while those with a pH greater than 7 are classified as basic or alkaline.
The optimal approach for measuring the pH of drilling fluid is to use a glass-electrode pH meter, which provides accurate and reliable pH readings without interference when paired with a high-quality electrode system and a well-designed instrument It is advisable to choose robust pH meters that automatically compensate for temperature variations, as they are superior to those requiring manual adjustments.
Colour-matching pH paper and sticks are not recommended for field pH measurements due to their unreliability in complex water-based drilling fluids These methods can produce significant errors in pH values when used with drilling fluid solids, dissolved salts, chemicals, and dark-coloured liquids, typically resulting in a readability of about 0.5 pH units.
Reagents and apparatus
To calibrate and set the slope of a pH meter before measuring samples, use the following buffer solutions: For pH 4.0, prepare a solution of potassium hydrogen phthalate at 0.05 mol/l in water, which yields a pH of 4.01 at 24 °C (75 °F) For pH 7.0, mix potassium dihydrogen phosphate at 0.02066 mol/l and disodium hydrogen phosphate at 0.02934 mol/l in water, resulting in a pH of 7.00 at 24 °C (75 °F) Lastly, for pH 10.0, combine sodium carbonate and sodium bicarbonate, both at 0.025 mol/l in water, achieving a pH of 10.01 at 24 °C (75 °F).
Buffers can be sourced from supply houses in the form of pre-made solutions, dry-powder packages, or specific formulas It is essential to note that all buffers have a shelf life of no more than six months and should be disposed of after this period The preparation date must be clearly labeled on the bottles used in the field, and these bottles should always be kept tightly stoppered to maintain their integrity.
11.2.2 Distilled or deionized water, in spray bottle
11.2.4 Sodium hydroxide, (CAS No 1310-73-2), 0,1 mol/l (approximately), to recondition electrode
DANGER — NaOH is a strong caustic alkaline chemical Avoid skin contact
11.2.5 Hydrochloric acid, (CAS No 7674-01-0), 0,1 mol/l (approximately), to recondition electrode
DANGER — HCl is a strong and toxic acid
11.2.6 Ammonium bifluoride (CAS No 1341-49-7), 10 % solution (approximately), to recondition electrode DANGER — Ammonium bifluoride is toxic and corrosive Handle accordingly and avoid skin contact
11.2.7 Millivolt-range potentiometer, calibrated to show pH units for measuring the potential between a glass- membrane electrode and a standard “reference” electrode
The ideal instrument should be portable and resistant to water, shock, and corrosion Key specifications include a pH range of 0 to 14, solid-state electronics, and a preferred battery power source It should operate within a temperature range of 0 °C to 66 °C (32 °F to 150 °F) and feature a digital readout The instrument must have a resolution, accuracy, and repeatability of 0.1 pH unit, ensuring precise measurements.
“temperature” compensation of electrode system;
“slope” of electrode system (preferred);
“calibration” setting of readout (Instrument with the above internal temperature compensation is preferred.)
11.2.8 Electrode system, a combination of a glass electrode for sensing H ions and a standard voltage reference electrode, preferably constructed as a single electrode
For optimal performance, the probe should be made from durable materials, with a flat-end design for enhanced protection and easier cleaning of the electrode It is advisable to use a waterproof connection to the meter The specifications include a glass pH electrode with a response range of 0 to 14 pH units, featuring a combination of a glass electrode and a silver/silver chloride electrode, which can have either a ceramic or plastic single or double junction.
When measuring liquids containing sulfide or bromide ions, it is essential to use a double-junction electrode to protect the silver reference electrode system from damage The reference electrode should contain a KCl gel electrolyte, and the glass composition must be appropriate to minimize sodium-ion error At a pH of 13 or with a sodium ion concentration of 0.1 mol, the sodium-ion error should remain below 0.1 pH unit.
11.2.9 Tissue, soft, to blot electrodes
11.2.11 Test-tube brush, soft bristle, to clean electrode
11.2.12 Electrode-storage vial, to keep electrodes moist.
Procedure for pH measurement
11.3.1 Obtain a sample of fluid to be tested Allow it to reach 24 °C 3 °C (75 °F 5 °F)
11.3.2 Allow buffer solution to reach the same temperature as the fluid to be tested
For precise pH measurement, it is essential that the test fluid, buffer solution, and reference electrode are all at the same temperature as the sample The pH value of the buffer solution, as stated on the container label, is accurate only at a temperature of 24 °C (75 °F).
When calibrating at a different temperature, it is essential to use the actual pH of the buffer at that specific temperature Suppliers provide tables of buffer pH values at various temperatures, which should be utilized during the calibration process.
11.3.3 Clean electrodes by washing with distilled water and blot dry
11.3.4 Place probe into pH 7,0 buffer
11.3.5 Turn on meter; wait 60 s for reading to stabilize (see 11.4 if meter reading is not stable)
11.3.6 Measure temperature of pH 7,0 buffer solution
11.3.7 Set this temperature on “temperature” knob
11.3.8 Set meter reading to “7,0” using “calibration” knob
11.3.9 Rinse probe with distilled water and blot dry
Repeat the procedures outlined in sections 11.3.6 to 11.3.9 using a buffer solution of either pH 4.0 or pH 10.0 Choose pH 4.0 for testing acidic samples and pH 10.0 for alkaline samples Ensure the meter is set to the corresponding pH value of either 4.0 or 10.0 as required.
“slope” adjustment knob (If no “slope” knob exists, use the “temperature” knob to set “4,0” or “10,0” on meter.)
11.3.11 Check the meter again with pH 7,0 buffer If it has changed, reset to “7,0” with “calibration” knob Repeat
11.3.6 through 11.3.9 If meter does not calibrate properly, recondition or replace electrodes as given in 11.4
It is essential to discard and not reuse the buffer solutions used for calibration The meter must be fully calibrated daily, following sections 11.3.2 to 11.3.9, utilizing two buffer solutions Additionally, when the meter is used continuously, check with a pH 7.0 buffer every three hours and before use if more than three hours have passed since the last measurement.
11.3.12 If meter calibrates properly, rinse electrode with distilled water and blot dry Place electrode in sample to be tested and stir gently Allow 60 s to 90 s for reading to stabilize
11.3.13 Record sample pH to nearest 0,1 pH unit and the temperature of sample
11.3.14 Carefully clean the electrode in preparation for next usage Store in vial of pH 4,0 buffer Never let the probe tip become dry
11.3.15 Turn meter off and close cover to protect instrument Avoid storing instrument at extreme temperatures
Care of electrode
Regular cleaning of electrodes is essential, particularly when oil or clay particles accumulate on the glass electrode's surface or the porous frit of the reference electrode To clean the electrode, use a soft-bristle brush along with a mild detergent.
11.4.2 Reconditioning the electrode can be necessary if plugging becomes severe, as indicated by a slow response, drifting of readings, or if “slope” and “calibration” cannot be mutually set
11.4.3 Recondition by soaking electrode for 10 min in 0,1 mol/l HCl, followed by rinsing in water and soaking for
10 min in 0,1 mol/l NaOH and rinsing again
11.4.4 Check electrode for response by performing calibration in 11.3.1 through 11.3.15
11.4.5 If electrode continues to perform poorly, soak electrode for 2 min only in 10 % ammonium bifluoride solution Repeat 11.3.1 through 11.3.15 to check for calibration capability
11.4.6 Replace electrode system if steps 11.4.3 to 11.4.5 fail to recondition it
Principle
Alkalinity refers to the acid-neutralizing capacity of a substance, and in drilling fluid testing, it can be measured for the entire drilling fluid (noted as “df”) or for the filtrate (noted as “f”) The results from alkalinity tests are valuable for estimating the concentrations of hydroxyl (\$[OH^-]\$), carbonate (\$[CO_3^{2-}]\$), and bicarbonate (\$[HCO_3^-]\$) ions present in the drilling fluid.
Understanding the alkalinities of drilling fluid and filtrate is crucial for effective drilling operations, as it helps maintain proper control over the fluid's chemistry Certain drilling fluid additives, especially deflocculants, depend on an alkaline environment for optimal performance While alkalinity from hydroxyl ions is typically advantageous, alkalinities derived from carbonates or bicarbonates can negatively impact the performance of the drilling fluid.
The primary ions responsible for filtrate alkalinities are hydroxyl (OH⁻), carbonate (CO₃²⁻), and bicarbonate (HCO₃⁻) ions The carbonate species can transform between different forms depending on the solution pH Accurately interpreting filtrate alkalinities requires calculating differences between titration values obtained through specific procedures, making precise measurement of reagents crucial at every step It is also essential to understand that the calculations provided are estimates of the concentrations of the ionic species based on theoretical chemical equilibrium reactions.
The complexity of drilling fluid filtrates can lead to misleading interpretations of alkalinities based on estimated ionic components Each alkalinity value reflects the ions reacting with acid within a specific pH range, including hydroxyl, carbonate, bicarbonate, borates, silicates, sulfides, and phosphates Anionic organic thinners and filtrate reducers, along with their degradation products, significantly contribute to alkalinity and can obscure endpoint color changes, particularly affecting the M f alkalinity test's accuracy in treated drilling fluids In contrast, for simple bentonite-based drilling fluid systems without organic thinners, the P f and M f alkalinities can serve as effective guidelines for identifying carbonate/bicarbonate contamination and determining necessary treatments.
Reagents and apparatus
12.2.1 Sulfuric acid (CAS No 7664-93-9) solution: standardized 0,02 N (N/50)
DANGER — H 2 SO 4 is a strong and toxic acid
12.2.2 Phenolphthalein (CAS No 518-51-4) indicator solution: 1 g/100 ml in 1:1 alcohol:water solution
12.2.3 Methyl orange (CAS No 547-58-0) indicator solution: 0,1 g/100 ml of water
NOTE A pH meter is more accurate than an indicator solution
12.2.5 Titration vessel, 100 ml or 150 ml, preferably white
12.2.6 Graduated pipettes, 1 ml (TD) and 10 ml (TD)
Procedure — Phenolphthalein and methyl orange filtrate alkalinities
Measure a specific volume of filtrate into the titration vessel and add a few drops of phenolphthalein indicator solution If the solution turns pink, gradually add 0.02 N sulfuric acid from a graduated pipette while stirring, until the pink color disappears If the sample is colored and the indicator's color change is not visible, determine the endpoint when the pH reaches 8.3, using a pH meter (refer to Clause 11 for accurate pH measurement).
12.3.2 Report the phenolphthalein alkalinity, P f , of the filtrate as the number of millilitres of 0,02 N acid required per millilitre of filtrate
To determine the endpoint of the titration, add two or three drops of methyl orange indicator solution to the sample that has been titrated to the P f endpoint Gradually add the standard acid from the pipette while stirring, until the indicator changes color from yellow to pink Alternatively, the endpoint can be identified when the pH of the sample reaches 4.3, as measured by a pH meter (refer to Clause 11 for accurate pH measurement).
Report the methyl orange alkalinity, denoted as \( M_f \), of the filtrate in terms of the total millilitres of 0.02 N acid needed per millilitre of filtrate to achieve the methyl orange endpoint, including the volume necessary for the \( P_f \) endpoint.