ISO/FDIS 13503-9

ISO/DISFDIS 13503-9:2025(en)
ISO/TC 67/SC 3
Secretariat: UNI
Date: 2025-07-292026-01-13
Oil and gas industries including lower carbon energy — Completion
fluids and materials — —
Part 9:
Methods for evaluating performance of acidizing fluids
Industries du pétrole et du gaz, y compris les énergies à faible teneur en carbone — Fluides de complétion et
matériaux —
Partie 9: Méthodes d'évaluation des performances des fluides acidifiants
FDIS stage
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ii
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Hydrochloric acid acidizing fluid system . 3
5.1 Corrosion rate assessment . 3
5.2 Acid rock reaction rate . 10
5.3 Dissolution rate . 13
3+
5.4 Ability to stabilize ferric ion (Fe ) . 16
5.5 Surface tension . 20
5.6 Interfacial tension . 25
6 Mud acid acidizing fluid system . 28
7 Polymer-based acid acidizing fluid system . 28
8 Emulsified acid acidizing fluid system . 28
9 Organic acid acidizing fluid system . 28
10 Other acidizing fluid system . 28
11 Test report . 28
Annex A (informative) Mud acid acidizing fluid system performance evaluation method . 30
Annex B (informative) Polymer-based acid acidizing fluid system performance evaluation
method . 34
Annex C (informative) Emulsified acid acidizing fluid system performance evaluation method 41
Bibliography . 43

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
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ISO documentdocuments should be noted. This document was drafted in accordance with the editorial rules
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This document was prepared by Technical Committee ISO/TC 67, Oil and gas industries including lower carbon
energy, Subcommittee SC 3, Drilling and completion fluids, well cements and treatment fluids.
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Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv
FINAL DRAFT International Standard ISO/FDIS 13503-9:2025(en)

Oil and gas industries including lower carbon energy – — Completion
fluids and materials —
Part 9:
Methods for evaluating performance of acidizing fluids
1 Scope
This document specifies the performance test procedures for acidizing fluids used as completion fluids and
materials in oil and gas well operations.
NOTE The acidizing fluids mentioned in this document refer to hydrochloric acid, mud acid, polymer-based acid
acidizing fluids, emulsified acid acidizing fluids, etc., used in acidizing operations of oil and gas wells, including
3+
fundamental acid solution and acidizing fluid system with additives, such as corrosion inhibitor and ferric ion (Fe )
stabling agent.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 3310-1:2016, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ASTM G111-21 Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or
Both
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
3.1
fundamental acid solution
A solution composed of acid and water containswith no other additives.
3.2
hydrochloric acid acidizing fluid system
hydrochloric acid mixed with functional additives to enhance its operational performance in specific industrial
applications, which is used to stimulate carbonate formations
3.3
mud acid acidizing fluid system
mixture of hydrofluoric acid, functional additives and water in certain concentration, which is used to acidify
sandstone reservoirs
3.4
polymer-thickened acid acidizing fluid system
acid system mixed with polymer to reduce friction, retard acid-rock reaction and uniform acid distribution
3.5
polymer-crosslinked acid acidizing fluid system
polymer-thickened acid acidizing fluid system (3.4) mixed with crosslinking agent to further enhance system
viscosity
3.6
emulsified acid acidizing fluid system
emulsified fluid system composed of acid-phase mixed with functional additives and another immiscible phase
3.7
organic acid acidizing fluid system
organic acids mixed with functional additives
4 Principle
In the test methods, the test conditions, acidizing fluid systems preparation and formulations shall be specified
by the supplier or entrusting party. If not specified, the operations shall be performed in accordance with the
methods specified in this document.
The following safety precautions shall be implemented:
a) a) Wear appropriate personal protective equipment, such as acid-resistant gloves, goggles, full face toxic
gas mask and clothing, to avoid acid contact with skin and eyes.
b) b) Carry out acidizing fluid systems preparation in a well-ventilated environment to avoid the
accumulation and inhalation of volatile gases.
c) c) Strictly follow the operating procedures, add acid to water instead of adding water to acid, and stir
continuously to prevent local overheating or acid splashing.
d) d) Containers, tools etc. used for preparation shall be made of acid-resistant and corrosion-resistant
materials to avoid acid leakage.
e) e) In case of acid leakage or contact with human body, timely treatment shall be carried out with
emergency treatment equipment, such as eyewash stations, shower devices and alkaline substances for
neutralization (ege.g. baking soda).
f) f) Once the acid contact with skin, immediately flush the skin with water for more than 15 minutes, apply
calcium gluconate gel and seek medical advice.
g) g) Equip with a dedicated eyewash, shower device, and 2,5 % calcium gluconate solution.
h) h) Usage of glass containers is prohibited, use plastic containers such as polytetrafluoroethylene (PTFE)
and polyethylene (PE) instead. Metal components shall be made of hydrofluoric acid-resistant alloys.
i) i) When connecting cables to experimental related equipment such as displacement pumps and pressure
sensors, ensure that the instruments are turned off.
j) j) After the experiment, timely clean the pipelines and containers that have contacted with the acidizing
fluid system to avoid corrosion of the residual liquid.
k) k) The experimental area shall be well ventilated, especially when using volatile substances likesuch as
acidizing fluid systems. Ventilation equipment shall be turned on to avoid the accumulation of harmful
gas.
5 Hydrochloric acid acidizing fluid system
5.1 Corrosion rate assessment
5.1.1 Purpose
The purpose of the corrosion rate test is to evaluate the damage degree of downhole metal materials exposed
in acid during acid treatment.
5.1.2 General
The acidizing fluid system has serious corrosion to tubing, casing, downhole tools etc. The corrosion rate test
is to measure the corrosion rate and pitting index of acidizing fluid systems on metal coupons, at a specific
temperature and exposure time.
1)
5.1.3 Reagents and materials materials
®1) ®
5.1.3.1 Hydrochloric acid: (HCl, 36,46 g/mol, CAS-No: : 7647-01-0) ).
® ®
5.1.3.2 Trichloroethylene: (C₂HCl₃, (C HCl , 131,39 g/mol, CAS-No: : 79-01-6) ).
2 3
® ®
5.1.3.3 Sodium Bicarbonate: (NaHCO₃,bicarbonate (NaHCO , 84,01 g/mol, CAS-No: : 144-55-8) ).
® ®
5.1.3.4 Acetone: (C₃H₆O (C H O, 58,08 g/mol, CAS-No: : 67-64-1) ).
3 6
® ®
5.1.3.5 Methanol: (CH₃OH (CH OH, 32,04 g/mol, CAS-No: : 67-56-1) ).
® ®
5.1.3.6 Diethyl ether（C₄H₁₀O (C H O, 74,12 g/mol, CAS-No: : 60-29-7) ).
4 10
____________________________________________ ®
1) CAS Registry Number is a trademark of the American Chemical Society (ACS). This information is given for the convenience of
users of this document and does not constitute an endorsement of the product by ISO of the product named. Equivalent products may ®
be used if they can lead to the same results. All symbols in this document share identical definitions.

5.1.4   Apparatus
5.1.4.1 High-temperature and high-pressure testing corrosion apparatus, as shown in Figure 1.

1) ®
CAS Registry Number is a trademark of the American Chemical Society (ACS). This information is given for the
convenience of users of this document and does not constitute an endorsement of the product by ISO of the product
named. Equivalent products may be used if they can lead to the same results.

High-
Key
1 pump
2 temperature and high-sensor
3 preheating kettle
4 pressure testing corrosion apparatus is shown in Figure 1.relief port

Key
1 pump
2 temperature sensor
3 preheating kettle
4 pressure relief port
5 rotor motor
6 pressure sensor
7 reaction kettle
8 sampling port
9 safety valve
10 sample holder
5 rotor motor
6 pressure sensor
7 reaction kettle
8 sampling port
9 safety valve
10 sample holder
Figure 1 — High-temperature and high-pressure testing corrosion apparatus
a) Figure 1The above Figure 1 is only a schematic diagram. The authoritative sourceASTM G111-21 contains
requirements for the instrument's design and fabrication is ASTM G111-21, Clause 6
Apparatusmanufacture of the instruments.
b) When heating the whole system set, the cooling circulating water system shall be running in order to
protect the rotor motor.
c) During the experimental process, if there is any leaking, stop the test immediately, unload the system
pressure, retighten the leaked part, and restart the test.
d) When using pump to pressurize, check the liquid level of the pump to avoid the abnormal system
operation due to insufficient liquid.
e) During the process of filling test liquid, spilling of the test liquid from either the preheating kettle or
reaction kettle is strictly prohibited.
f) When closing the lid of the preheating kettle and the reaction kettle, the lid shall be tightened and then
rotated 1/4 turn in the opposite direction.
g) When cleaning the corrosive liquid, pay attention to the recovery of waste liquid to avoid polluting the
environment.
h) The instrument shall be maintained properly and periodically. Maintenance shall be carried out once a
week, with each session lasting for half a day.
i) Metal coupons, the metal coupon dimensions are specified as: 30 mm wide × 15 mm long × 3,6 mm thick
with a 5 mm-diameter hole drilled through the centercentre.
The metal coupons are shown in Figure 2Figure 2.
Dimensions in millimetres
Figure 2 — Metal coupons parameters
5.1.4.2 Electronic balances, with a precision of 0,0001 000 1 g to 0,01 g.
5.1.4.3 Stirrer.
5.1.4.4 Stopwatches, with an accuracy of ±0,1 s.
5.1.4.5 Dryer.
5.1.4.6 Electric blast drying oven, capable of being controlled at 100 °C ± ± 1 °C.
5.1.4.7 Electric blast drying ovens, with a temperature control range of 100 °C ± ± 1 °C.
5.1.4.8 Measuring cylinders, with capacities of 100 ml and 500 ml, respectively.
5.1.4.9 Beakers, with capacities of 250 ml and 1000 1 000 ml, respectively.
5.1.4.10 Glass jars, with a capacity of 500 ml.
5.1.4.11 PTFE bottles, with a capacity of 500 ml.
5.1.4.12 Abrasive paper, 120-grit.
5.1.5 Preparation and preservation of test samples and pieces
5.1.5.1 Hydrochloric acid acidizing fluid system preparation
a) a) Hydrochloric acid solution preparation
Based on the mass fraction needed, calculate the mass of hydrochloric acid and distilled water required to
prepare hydrochloric acid solution according to Formulae (1)Formula (1) and (2)(2). During system
configuration, hydrochloric acid shall be added to distilled water with continuous stir until the solution is
uniform. After constant mass, it shall be stored in a glass vial waiting for use.
Calculate the mass of hydrochloric acid using Formula (1)Formula (1).:
𝑚𝑚𝑚𝑚
𝑚𝑚 = (1)
𝑚𝑚
where
𝑚𝑚 is mass of hydrochloric acid, in g
𝑚𝑚 is mass of hydrochloric acid solution, in g
𝑊𝑊 is mass fraction of hydrogen chloride in hydrochloric acid solution, in %
𝑊𝑊 is mass fraction of hydrogen chloride in hydrochloric acid, in %
𝑚𝑚 is the mass of hydrochloric acid, in g;
𝑚𝑚 is the mass of hydrochloric acid solution, in g;
𝑊𝑊 is the mass fraction of hydrogen chloride in hydrochloric acid solution, in %;
𝑊𝑊 is the mass fraction of hydrogen chloride in hydrochloric acid, in %.
Calculate the mass of distilled water using Formula (2)Formula (2).:
𝑚𝑚 𝑚𝑚 =𝑚𝑚−𝑚𝑚 (2)
𝑤𝑤 w 0
where 𝑚𝑚 𝑚𝑚 is the mass of distilled water used in hydrochloric acid solution preparation, in g.
𝑤𝑤 w
The following is an example of preparing 500 g of 20 % hydrochloric acid solution using 37 % hydrochloric
acid.
500×20 % 500×20 %
Mass of hydrochloric acid, 𝑚𝑚𝑚𝑚 = 270,27 g g (𝑚𝑚𝑚𝑚 = ). ). Mass of distilled water, 𝑚𝑚 𝑚𝑚 =
𝑜𝑜 0 𝑜𝑜 0 𝑤𝑤 w
37 % 37 %
229,73 g g (𝑚𝑚 𝑚𝑚 = 500 to  to 270,27). During the preparation, hydrochloric acid shall be added to distilled
𝑤𝑤 w
water with continuous stir until uniform.
b) b) Hydrochloric acid acidizing fluid system preparation
When preparing hydrochloric acid acidizing fluid system, the mass of hydrochloric acid is calculated according
to Formula (1)formula (1),, and other additives shall be added accordingly based on mass fraction. Calculate
the mass of additives using Formula (3)Formula (3),, which shall be subtracted from the distilled water.:
𝑚𝑚 𝑚𝑚 =𝑚𝑚𝑊𝑊𝑊𝑊 (3)
𝑛𝑛 n 𝑛𝑛 n
where
𝑚𝑚 is mass of additives, in g
𝑛𝑛
𝑊𝑊 is mass fraction of additives, in %
𝑛𝑛
𝑚𝑚 is the mass of additives, in g;
n
𝑊𝑊 is the mass fraction of additives, in %.
n
Calculate the mass of distilled water using Formula (4)Formula (4).:
𝑚𝑚' ′ =𝑚𝑚 𝑚𝑚 −𝑚𝑚 (4)
𝑤𝑤w 𝑤𝑤 w 𝑛𝑛n
where 𝑚𝑚' ′ is the mass of distilled water used in hydrochloric acid acidizing fluid system preparation, in g.
𝑤𝑤w
The following is an example.
Conditions and requirements: 500 g hydrochloric acid acidizing fluid system shall be prepared with 37 %
hydrochloric acid.
Hydrochloric acid acidizing fluid system formulation: 20 % hydrochloric acid solution + 3 % corrosion
inhibitor + 0,5 % flowback aid.
The mass of additives shall be calculated by mass fraction: the mass of corrosion inhibitor = 500 g × 3 % =
15 g, and the mass of flowback aid = 500 g × 0,5 % = 2,5 g. The mass of distilled water = 229,73 – 15 – 2,5 =
212,23 g. During the preparation, hydrochloric acid shall be added to distilled water with continuous stir until
uniform. Then, 15 g corrosion inhibitor and 2,5 g flowback aid shall be added, stirred uniformly, and kept in a
glass jar until use.
5.1.5.2 Metal coupons preparation
a) a) Cleaning of metal coupons before test
The metal coupons shall first be rinsed with a suitable solvent, such as acetone, methanol or a mixture of 50 %
methanol and 50 % diethyl ether. Then, the metal coupons shall be scrubbed with a bleach-free scouring
powder or 120-grit abrasive paper, soaked in trichloroethylene for degreasing, and scrubbed with a nylon
brush in tap water. Next, the metal coupons shall be rinsed and soaked with a suitable solvent again, such as
acetone, methanol or a mixture of 50 % methanol and 50 % diethyl ether. After being dried in an electric blast
drying oven, the metal coupons shall be placed in a dryer. The dried metal coupons shall be weighed with an
analytical balance, and shall be repeatedly cleaned and dried until constant mass is achieved, which is
recorded as 𝑚𝑚 (accurate to 0,0001 000 1 g).
b) b) Cleaning of metal coupons after test
The metal coupons shall be scrubbed with a nylon brush in tap water, rinsed and soaked with a suitable
solvent, such as acetone, methanol or a mixture of 50 % methanol and 50 % diethyl ether. After being dried in
an electric blast drying oven, the metal coupons shall be placed in a dryer. The dried metal coupons shall be
weighed with an analytical balance, and repeatedly cleaned and dried until constant mass is achieved, which
is recorded as 𝑚𝑚 (accurate to 0,0001 000 1 g).
5.1.6 Static corrosion rate test procedure
5.1.6.1 The number of metal coupons and the volume of acidizing fluid system depend on the total
immersed surface area of metal coupons. The ratio of the surface area of metal coupons (in cm²)cm ) to the
volume of the acidizing fluid system (in ml) shall be ≤ 1:20.
5.1.6.2 Pour acidizing fluid system into a glass jar (PTFE liner for mud acid acidizing fluid system) and place
it in an electric thermostatic water bath (95 °C).
5.1.6.3 Heat the acidizing fluid system to the desired experimental temperature.
5.1.6.4 Thread the plastic thin wire through the hole of the cleaned metal coupons, then place the metal
coupons in a glass jar (use a Teflon container for the mud acidizing fluid system). Adjust the length of the wire
so that the cleaned metal coupons are completely immersed and suspended in the acidizing fluid system.
5.1.6.5 Start the stopwatch, the reaction shall continue until 4 h or under the specific conditions provided
by the supplier. After that, the metal coupons shall be taken out for treatment and analysis (5.1.5.2[5.1.5.2
b).)].
5.1.6.6 Carry out three parallel determinations. If the difference between calculated values is no more than
0,5 %, take the arithmetic mean as the result.
5.1.7 Dynamic corrosion rate test procedure
5.1.7.1 Calculate the volume of acidizing fluid system. The volume of acidizing fluid system depends on the
surface area of metal coupons. The ratio of the surface area of metal coupons (in cm²)cm ) to the volume of
the acidizing fluid system (in ml) shall be ≤ 1:20.
5.1.7.2 Install cleaned metal coupons into the sample holder of the high-temperature and high-pressure
corrosion apparatus.
5.1.7.3  PSlowlySlowly pour acidizing fluid system into the preheating kettle.
5.1.7.4 Set the desired temperature and stir rate.
5.1.7.5 Once reachreached the set temperature, pressurize the preheating kettle to push acidizing fluid
system from the preheating kettle to the reaction kettle, then close the valve between two kettles.
5.1.7.6 Pressurize the reaction kettle to the test pressure (normally 16 MPa) by pump, then dynamic
corrosion rate test begins.
5.1.7.7 Once the test is finished (normally performed for 4 h), open the valve between two kettles and push
back the acidizing fluid system to the preheating kettle.
5.1.7.8 Set the temperature to 0 °C, stop heating and allow both kettles to cool sufficiently.
5.1.7.9 After the temperature decreases to a relatively safe level (recommended below 50 °C), slowly and
completely discharge the remaining acidizing fluid system and decompress the equipment system. Drain the
acidizing fluid system and its vapor into a large bottle filled with coolant.
5.1.7.10 Open the water valve, thoroughly flush both kettles and pipelines until they are completely cleaned.
5.1.7.11 Open the reaction kettle and take the metal coupons out for treatment and analysis (5.1.5.2[5.1.5.2
b).)].
5.1.7.12 Carry out three parallel determinations. If the difference between calculated values is no more than
0,5 %, take the arithmetic mean as the result.
5.1.8 Calculation
Calculate the corrosion rate using Formula (5)Formula (5):
(𝑚𝑚 −𝑚𝑚 )×10
1 2
𝑣𝑣 = (5)
𝑡𝑡𝐴𝐴
where:
𝐴𝐴 is surface area of tested metal coupons, in cm
𝑣𝑣 is corrosion rate, in g/(m ·h)
𝑚𝑚 is mass of metal coupons before test, in g
𝑚𝑚 is mass of metal coupons after test, in g
𝑡𝑡 is experimental time, in h
𝐴𝐴 is the surface area of tested metal coupons, in cm ;
𝑣𝑣 is the corrosion rate, in g/(m ·h);
𝑚𝑚 is the mass of metal coupons before test, in g;
𝑚𝑚 is the mass of metal coupons after test, in g;
𝑡𝑡 is the experimental time, in h.
5.2 Acid rock reaction rate
5.2.1 Purpose
Acid rock reaction rate is an important index, which determines the treating distance of acidizing fluid systems
and can be measured by hydrogen ion consumption rate in different reaction stages.
5.2.2 General
During the reaction between acidizing fluid systems and the carbonate core under reservoir conditions,
residual acid samples are taken at different time points. Hydrogen ion concentration is measured by titration,
which is then used for the calculation of acid rock reaction rate.
5.2.3 Reagents and materials
® ®
5.2.3.1 Hydrochloric acid (HCl, 36,46 g/mol, CAS-No: : 7647-01-0) .).
® ®
5.2.3.2 Sodium hydroxide (NaOH, 40,00 g/mol, CAS-No: : 1310-73-2) .).
® ®
5.2.3.3 Ethanol (C₂H₅OHC H OH, 95 %, CAS-No: : 64-17-5) .).
2 5
® ®
5.2.3.4 Phenolphthalein (C₂₀H₁₄O₄,C H O , 318,32 g/mol, CAS-No: : 77-09-8) .).
20 14 4
5.2.3.5 Carbonate core.
5.2.4 Apparatus
5.2.4.1 High-temperature and high-pressure testing corrosion apparatus, see Figure 1Figure 1.
5.2.4.2 Electronic balances, with a precision of 0,0001 000 1 g to 0,01 g.
5.2.4.3 Vernier calipers, with a precision of 0,02 mm.
5.2.4.4 Pipettes, with capacities of 1 ml, 5 ml and 10 ml, respectively.
5.2.4.5 Burette, for titration, with a precision of 0,01 ml.
5.2.4.6 Conical flask, 100 ml or 250 ml. Conical flasks, with capacities of 100 ml andorand 250 ml,
respectively.
5.2.4.7 Volumetric flask, 1000 mlVolumetric flasks, with a capacity of 1000 1 000 ml.
5.2.4.8 Dryer.
5.2.5 Preparation and preservation of test samples and test pieces
5.2.5.1 Hydrochloric acid acidizing fluid system preparation
.
For a description of the hydrochloric acid acidizing fluid system preparation, see 5.1.5.15.1.5.1.
5.2.5.2 Core sample preparation
a) a) Cut cylindrical core samples and polish the surfaces with a grinding machine to ensure regular edges
and smooth surfaces.
b) b) The standard core dimensions shall be 25,4 mm in diameter and 25,4 mm in length.
c) c) The polished core shall beisbe cleaned with ethanol to remove surface impurities, dried with cold air,
and stored in a dryer until use.
d) d) Measure the core dimensions using a vernier caliper and calculate the surface area of the bottom end
of the core (𝐴𝐴 ).A ).
e) e) Fix the core at the end of the sample holder with heat-shrink teflon tubing or with high-temperature
epoxy resin. Wrap the whole core except the bottom end with heat-shrink teflon tubing or high-
temperature epoxy resin to ensure only the bottom end of the core can react with acid.
5.2.5.3 Volume of hydrochloric acid acidizing fluid system
The volume of acidizing fluid system (V_HClV ) is determined by the core surface area. The ratio of the
HCl
surface area of the core (in cm²)cm ) to the volume of the hydrochloric acid acidizing fluid system (in ml) shall
be 1:(20 to 40). Meanwhile, the volume of acidizing fluid system shallouldshall be less than the safety capacity
of the reaction kettle.
5.2.5.4 Phenolphthalein indicator solution preparation
Dissolve 1,0 g of phenolphthalein in 50 ml of ethanol, then dilute to 100 ml with distilled water.
5.2.5.5 Sodium hydroxide standard solution preparation
a) Sodium hydroxide pellets shall be weighed using an analytical balance accurate to 0,000 1 g, the mass
(m ) should be 4 g.
NaOH
b) b) The solid is transferred to a small beaker and dissolved in carbon dioxide-free water.
c) c) Transfer the cooled solution completely to a 1000 1 000 ml volumetric flask, dilute to the mark and mix
thoroughly.
d) d) Store the solution in a reagent bottle with a rubber stopper.
5.2.6 Acid rock reaction rate test procedure
5.2.6.1 Place the sealing ring in the sample holder, put the core in, and close the reaction kettle. Pour the
acidizing fluid system to the preheating kettle.
5.2.6.2 Turn on the computer and enter the program, set the desired temperature, stir rate and the
automatic sampling interval.
5.2.6.3 Set the desired pressure. Open the valves for the preheating kettle, fluid lines, and reaction kettle
sequentially.
5.2.6.4 Once the set temperature is reached, pump the acidizing fluid system into the reaction kettle.
Maintain a continuous flow of acidizing fluid system to ensure consistent reaction conditions.
5.2.6.5 During acid rock reaction, the residual acidizing fluid system flows through a cooling device to
reduce temperature. Collect samples from the sampling port at predefined intervals or automatically using
the system'ssystem’s sampling mechanism.
5.2.6.6 Once the test is finished, push the acidizing fluid system back to the preheating kettle to stop the
acid rock reaction.
5.2.6.7 Set the temperature to 0 °C, stop heating and allow both kettles to cool sufficiently.
5.2.6.8 After the temperature decreases to a relatively safe level (recommended below 50 °C), completely
discharge the remaining acidizing fluid system and decompress the equipment system. Drain the acidizing
fluid system and its vapor into a large bottle filled with coolant.
5.2.6.9 Open the water valve, thoroughly flush both kettles and pipelines until they are completely cleaned.
5.2.7 Calculation
5.2.7.1 Residual acidizing fluid system sample collection
a) a) Take the residual acidizing fluid system sample according to 5.2.6.55.2.6.5.
′
′
b) b) 0,2 ml (𝑉𝑉 𝑉𝑉 ) of residual acidizing fluid system shall be transferred to a conical flask using a pipette.
HCl
𝐻𝐻𝐻𝐻𝐻𝐻
Prepare 2 parallel samples, and dilute with 20 ml of distilled water.
5.2.7.2 Titration
a) a) Add 2 drops of phenolphthalein indicator solution to the diluted sample.
b) b) Titrate the diluted sample with sodium hydroxide standard solution until the solution turns pink and
persists for 30 s. Record the consumed volume of sodium hydroxide standard solution.
c) c) Carry out three parallel determinations. If the maximum deviation is no more than 0,10 ml, take the
arithmetic mean as the result, denoted as 𝑉𝑉 . Otherwise, re-sample the residual acidizing fluid system
𝑁𝑁𝑁𝑁𝑁𝑁𝐻𝐻
for titration.
5.2.7.3 Calculation
A.1 Calculation
Calculate the molar concentration of hydrogen chloride in the residual acidizing fluid system sample using
Formula (6)Formula (6).:
𝑚𝑚 𝑉𝑉
𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁 𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁
𝐶𝐶 = (6)
𝐻𝐻𝐻𝐻𝐻𝐻
′
40×1×𝑉𝑉
𝑁𝑁𝐻𝐻𝐻𝐻
𝑚𝑚 𝑉𝑉
NaOH NaOH
𝐶𝐶 = (6)
HCl ′
40×1×𝑉𝑉
HCl
where
is molar concentration of hydrogen chloride in the residual acidizing fluid system sample, in
𝐶𝐶
𝐻𝐻𝐻𝐻𝐻𝐻
mol/L
𝑚𝑚 is mass of sodium hydroxide, in g
𝑁𝑁𝑁𝑁𝑁𝑁𝐻𝐻
𝑉𝑉 is volume of sodium hydroxide standard solution used for titration, in ml
𝑁𝑁𝑁𝑁𝑁𝑁𝐻𝐻
40 is molar mass of sodium hydroxide, in g/mol

1 is volume of sodium hydroxide standard solution prepared, in L
′
is volume of residual acidizing fluid system sample, in ml
𝑉𝑉
𝐻𝐻𝐻𝐻𝐻𝐻
𝐶𝐶 is the molar concentration of hydrogen chloride in the residual acidizing fluid system sample, in mol/l;
HCl
𝑚𝑚 is the mass of sodium hydroxide, in g;
NaOH
𝑉𝑉 is the volume of sodium hydroxide standard solution used for titration, in ml;
NaOH
40 is the molar mass of sodium hydroxide, in g/mol.
1 is the volume of sodium hydroxide standard solution prepared, in l;
′
𝑉𝑉 is the volume of residual acidizing fluid system sample, in ml.
HCl
5.2.8 Plotting the curve
a) Plot the acid rock reaction rate curve with reaction time (𝑡𝑡, in s) as the horizontal axis and molar
concentration of hydrogen chloride in the residual acidizing fluid system sample (𝐶𝐶 , in mol/Ll) as the
𝐻𝐻𝐻𝐻𝐻𝐻
vertical axis.
b) The acid rock reaction rate shall be calculated through the slope of the curve.
c) Calculate the acid rock reaction rate using Formula (7)Formula (7).:
−3 −3
𝑘𝑘𝑉𝑉 ×10 𝑘𝑘𝑉𝑉 ×10
𝑁𝑁𝐻𝐻𝐻𝐻 HCl
𝑅𝑅 =−𝑐𝑐 (7)
𝐴𝐴 𝐴𝐴
2 2
where
𝑅𝑅 is acid rock reaction rate, in g/(cm •s)
is a constant related to the type of carbonates, which is 50 for limestone and 46
𝑐𝑐
for dolomite, in g/mol
𝑘𝑘 is slope of the acid rock reaction rate curve, in mol/(L•s)

𝑉𝑉 is volume of hydrochloric acid acidizing fluid system, in ml
𝐻𝐻𝐻𝐻𝐻𝐻
𝐴𝐴 is surface area of core sample, in cm
𝑅𝑅 is the acid rock reaction rate, in g/(cm ∙s);
𝑐𝑐 is a constant related to the type of carbonates, which is 50 for limestone and 46 for dolomite, in g/mol;
𝑘𝑘 is the slope of the acid rock reaction rate curve, in mol/(l∙s);
𝑉𝑉 is the volume of hydrochloric acid acidizing fluid system, in ml;
HCl
𝐴𝐴 is the surface area of the core sample, in cm .
5.3 Dissolution rate
A.2A.1 Purpose
5.3.1 Purpose
The purpose of core dissolution rate is to evaluate the stimulating ability of acidizing fluid systems in
reservoirs.
5.3.15.3.2 General
The dissolution ability of acidizing fluid systems is evaluated through the mass loss of core powder after the
complete reaction with acidizing fluid systems under reservoir conditions.
5.3.25.3.3 Reagents and materials
® ®
5.3.2.15.3.3.1 Hydrochloric acid: (HCl, 36,46 g/mol, CAS-No: : 7647-01-0) ).
5.3.2.25.3.3.2 Core powder.
5.3.35.3.4 Apparatus
5.3.3.15.3.4.1 Electronic balances, with a precision of 0,0001 000 1 g to 0,01 g.
5.3.3.25.3.4.2 Electric heating constant temperature water baths, with a temperature control range of 100 °C
± ± 1 °C.
5.3.3.35.3.4.3 Electric heating constant temperature drying ovens, with a temperature control range of 250 °C
± ± 1 °C.
5.3.3.45.3.4.4 Dryer.
5.3.3.55.3.4.5 pH indicator paper, capable of measuring pH values in the range of 0,5 to 5,0 for precise
measurements and 1 to 14 for universal measurements.
5.3.3.65.3.4.6 Filter papers, with a pore size of 80 μm to 120 μm.
5.3.45.3.5 Preparation and preservation of test samples and test pieces
5.3.4.15.3.5.1 Hydrochloric acid acidizing fluid system preparation
For a description of the hydrochloric acid acidizing fluid system preparation, see 5.1.5.15.1.5.1. .
5.3.4.25.3.5.2 Core powder preparation
The pulverized core powder shall be passed through sieve sets with an aperture size of 150 μm and a diameter
of 0,15 mm, or sieve sets with other standard diameters as specified in ISO 3310-1:2016, Clause 4.1. Sieve sets,
and uniformly mixed. The prepared core powder and the quantitative filter paper shall be dried at 105 °C
± ± 1 °C for 4 h and cooled in a dryer for 30 min.
5.3.4.35.3.5.3 Filter paper weighing
Weigh the dried filter paper and record its mass as 𝑚𝑚 (accurate to 0,0001 000 1 g).
5.3.4.45.3.5.4 Usage of hydrochloric acid acidizing fluid system
a) Calculate the maximum mass of hydrochloric acid acidizing fluid system using Formula (8)Formula (8).:
2×36,5𝑥𝑥𝑚𝑚 𝑥𝑥𝑚𝑚
3 3
𝑚𝑚 𝑚𝑚 = = 0,73 (8)
𝑁𝑁𝑎𝑎𝑎𝑎𝑎𝑎 acid
100𝑦𝑦 𝑦𝑦
where
𝑚𝑚 is the maximum mass of hydrochloric acid acidizing fluid system used for dissolution rate test, in g
𝑁𝑁𝑎𝑎𝑎𝑎𝑎𝑎
𝑥𝑥 is mass fraction of calcium carbonate in core powder, in %
𝑦𝑦 is mass fraction of hydrogen chloride in hydrochloric acid acidizing fluid system, in %
𝑚𝑚 is mass of core powder used for dissolution rate test, in g
36,5 is molar mass of hydrogen chloride, in g/mol
100 is molar mass of calcium carbonate, in g/mol
b) 𝑚𝑚 is the maximum mass of hydrochloric acid acidizing fluid system used for dissolution rate test, in g;
acid
𝑥𝑥 is the mass fraction of calcium carbonate in core powder, in %;
𝑦𝑦 is the mass fraction of hydrogen chloride in hydrochloric acid acidizing fluid system, in %;
𝑚𝑚 is the mass of core powder used for dissolution rate test, in g;
36,5 is the molar mass of hydrogen chloride, in g/mol;
100 is the molar mass of calcium carbonate, in g/mol.
b) The dissolution ability of acidizing fluid system should be evaluated with an excess of core powder,
therefore, the mass of hydrochloric acid acidizing fluid system used for dissolution rate testing shall be
𝑥𝑥𝑚𝑚
less than 0,73 .
𝑦𝑦
5.3.55.3.6 Dissolution rate test procedure
a) Weigh the dried core powder and record its mass as 𝑚𝑚 m (recommended 1 g, accurate to 0,0001
000 1 g), then put it into a 100 ml plastic centrifuge tube with lid.
b) Completely add acidizing fluid system (for mass of acidizing fluid system, see 5.3.5.45.3.5.4 b) to the
centrifuge tube with dried core powder.
c) After the core powder is completely wetted by the acidizing fluid system, place the centrifuge tube in a
constant temperature hot water bath at reservoir temperature. If the reservoir temperature is above
95 °C, the experimental temperature shall be set to 95 °C.
d) Record the time when the centrifuge tube is placed in the hot water bath as the reaction start time.
e) After 2 h, take out the centrifuge tube. First filter the upper-layer acidizing fluid system with a quantitative
filter paper, then wash the residual acidizing fluid system and core powder in the centrifuge tube with
distilled water and completely transfer them onto the quantitative filter paper.
f) Rinse the quantitative filter paper with distilled water repeatly and test the pH of the filtrate with a precise
pH indicator paper until the pH is 7.
g) Dry the remaining core powder and the quantitative filter paper in an electric heating constant
temperature drying oven at 105 °C ± ± 1 °C for 4 h, then cool them in a dryer for 30 min.
h) Weigh the mass of filter paper with the remaining core powder, which is recorded as 𝑚𝑚 m (accurate to
0,0001 000 1 g).
i) Carry out three parallel determinations. If the difference between calculated values is no more than 0,5 %,
take the arithmetic mean as the result.
5.3.65.3.7 Calculation
Calculate the dissolution rate using Formula (9)Formula (9).:
𝑚𝑚+𝑚𝑚 −𝑚𝑚
3 4
𝜂𝜂 = × 100%(9) % (9)
𝑚𝑚
where
𝜂𝜂 is core dissolution rate, in %
𝑚𝑚 is mass of quantitative filter paper before test, in g
𝑚𝑚 is mass of core powder before test, in g
𝑚𝑚 is mass of quantitative filter paper with the remaining core powder after test, in g
𝜂𝜂 is the core dissolution rate, in %;
𝑚𝑚 is the mass of quantitative filter paper before test, in g;
𝑚𝑚 is the mass of core powder before test, in g;
𝑚𝑚 is the mass of quantitative filter paper with the remaining core powder after test, in g.
3+
5.4 Ability to stabilize ferric ion (Fe³⁺)Fe )
5.4.1 Purpose
3+
The purpose of ferric ion (Fe³⁺)Fe ) stabilizing agents performance test is to evaluate their ability to stabilize
3+
ferric ion (Fe³⁺)Fe ) in acidizing fluid systems during acid treatment, in order to prevent the damage to the
3+
reservoir caused by ferric ion (Fe³⁺)Fe ) precipitation.
5.4.2 General
Acidizing fluid systems react with downhole metal equipment and iron containing minerals in the formation
3+
during acid treatment, generating a large number of ferric ions (Fe³⁺)Fe ) dissolved in the residual acidizing
3+
fluid systems. When the pH rises to 2,2, ferric ions (Fe³⁺)Fe begin to form flocculent iron hydroxide
3+
precipitate. When the pH rises to 3,2, All dissolved ferric ions (Fe³⁺)Fe in the acidizing fluid system
3+
precipitate if no effective Fe³⁺Fe stabilizing agent is used.
3+
Prepare the acidizing fluid system containing ferric ion (Fe³⁺)Fe ) stabilizing agent, and add sodium
3+
carbonate into the system until the pH =is 4 to 5. Then add ferric ion (Fe³⁺)Fe standard solution into the
3+ 3+
system until ferric ions (Fe³⁺)Fe ) begin to precipitate. The amount of ferric ion (Fe³⁺)Fe standard solution
3+
added before precipitation is used to evaluate the ability to stabilize ferric ion (Fe³⁺) .Fe .
2 + 2 +
NOTE During acid treatment, the influence of ferrous ions (Fe⁺) ) can be ignored, since ferrous ions (Fe⁺) only
3+
begin to precipitate when the pH is above 5,8 and are easily oxidized to ferric ions (Fe³⁺). Fe .
5.4.3 Reagents and materials
® ®
5.4.3.1 Hydrochloric acid: (HCl, 36,46 g/mol, CAS-No: : 7647-01-0) ).
® ®
5.4.3.2 Sodium carbonate: (Na₂CO₃, (Na CO , 105,99 g/mol, CAS-No: : 497-19-8) ).
2 3
® ®
5.4.3.3 Ferric chloride hexahydrate: (FeCl₃·6H₂O (FeCl ·6H O, 270,30 g/mol, CAS-No: : 10025-77-1) ).
3 2
5.4.3.4 Disodium ethylenediaminetetraacetate: (C₁₀H₁₄N₂Na₂O₈·2H₂O (C H N Na O ·2H O,
10 14 2 2 8 2
® ®
372,24 g/mol, CAS-No: : 6381-92-6) ).
® ®
5.4.3.5 Sulfosalicylic acid: (C₇H₆O₆S (C H O S, 218,18 g/mol, CAS-No: : 5965-83-3) ).
7 6 6
® ®
5.4.3.6 Ammonia water: (NH₃·H₂O (NH ·H O, 35,05 g/mol, CAS-No: : 1336-21-6) ).
3 2
5.4.4 Apparatus
5.4.4.1 Electronic balances, with a precision of 0,0001 000 1 g to 0,01 g.
5.4.4.2 Stirrer.
5.4.4.3 Pipettes, with capacities of 1 ml, 5 ml and 10 ml, respectively.
5.4.4.4 Beaker.
5.4.4.5 Volumetric flasks, with capacities of 500 ml and 1000 1 000 ml, respectively.
5.4.4.6 Pipettes, with capacities of 1 ml, 5 ml and 10 ml, respectively.
5.4.4.7 Electric heating constant temperature water baths, with a temperature control range of 100 °C
± ± 1 °C.
5.4.4.8 pH indicator paper, capable of measuring pH values in the range of 0,5 to 5,0 for precise
measurements and 1 to 14 for universal measurements.
5.4.5 Preparation and preservation of test samples and test pieces
5.4.5.1 Hydrochloric acid acidizing fluid system preparation
For a description of the hydrochloric acid acidizing fluid system preparation, see 5.1.5.15.1.5.1. .
3+
5.4.5.2 Ferric ion (Fe³⁺)Fe ) stabilizing agent solution preparation
3+ 3+
Transfer 10,00 ml of ferric ion (Fe³⁺
...