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Gravimetric Solubility225.020
Analytical Procedures Analytical & Materials QC
January 1999____ Page 2.5-6 Global Laboratory Best Practices,
Vol. 2
Gravimetric Solubility
Procedure No.: WM-GL-HES-QM-225.020
Description
This procedure is designed to measure the solubility of
formation samples, wellbore deposits,
produced solids, and fracturing proppants in acids and other
treatment fluids. Solubility data
obtained from this analysis supplement X-ray diffraction data
and are of interest for well treat-
ment designs.
Several different acids may be tested, but 15% hydrochloric acid
(HCl) and a mixture of 12%
HCl with 3% hydrofluoric acid (HF) are standard. American
Petroleum Institute procedures
for testing gravel-pack sands and proppants may differ slightly.
Consult these procedures
when necessary.
Equipment and Reagents
Procedure
SummaryTesting various formation samples for solubility yields
important information for well treat-
ment design processes. Samples are dried, ground to pass through
a 100-mesh sieve, weighed,
and then immersed in test fluid either for 60 minutes at 65C
(150F) or for the specified time
and temperature. At the end of the time period, the remaining
sample is cooled, filtered, and
dried, and finally weighed. Gravimetric solubility is calculated
from the weight lost relative to
the original sample weight.
Item Specifications Quantity
Analytical balance 1
Vacuum oven 1
Desiccator Requires a storage cabinet large
enough to handle the expectedsample load
1
Water bath 1
Hydrochloric acid (HCl) 15% solution As needed
Mixture of hydrochloric acid (HCl) and
hydrofluoric acid (HF)
HCl at 12% and HF at 3% As needed
Disposable filter assemblies Nalgene 130-4045 set including
a115-mL capacity plastic funnel with
filtrate receiver and 0.45-mm filter
One set
Glass and polyethylene beakers 250 mL with watch glass or
plasticlids to cover the top
As needed
Buchner funnel with Whatman filterpaper
One set
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Gravimetric Solubility 225.020
Analytical ProceduresAnalytical & Materials QC
Global Laboratory Best Practices, Vol. 2 Page 2.5-7 January 1999
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Sample Handling
NoteSamples should have a consistently low moisture content.
Oily or paraffin-coated
samples do not wet properly. Clean them with solvents before
drying.
1. Clean oily or paraffin-coated samples with chloroform,
acetone, or methanol with one ofthe following methods:
a. Rinse the sample with 25 to 50 mL of each solvent in a
Buchner funnel on Whatman
filter paper.
b. Shake the sample with a 50-mL aliquot of each solvent in a
centrifuge tube, spinning
the solids between each step and discarding solvents in an
appropriate disposal
container.
2. The cleaning procedure should yield 10 g for the solubility
test. Dry the sample at 65C
(150F) in an oven for at least one hour. Store the dried sample
in a desiccator.
CautionWear safety glasses when handling acids. Wear gloves and
a laboratory coator apron to protect clothing, especially when
handling hydrofluoric acid (HF).
Standards Preparation
1. To prepare 15% HCl solution, dilute 800 mL of concentrated,
reagent grade HCl to 2 L
with deionized (D.I.) water in a volumetric flask. This dilution
is convenient to store and
is ready to use.
2. To prepare 12% HCl-3% HF mixture, do the following:
a. Dilute 594 mL of concentrated reagent grade HCl with D.I.
water.
b. Add either 100 mL of 52% concentrated HF or 92.6 g of
ammonium bifluoride (ABF)solid reagent.
c. Dilute the sample to 2 L with D.I. water.
Main Procedure
1. Dry a Nalgene disposable filter at 65C (150F) for 30
minutes.
2. Cool the filter to room temperature in a desiccator and weigh
it to the nearest 0.0001 g
with an analytical balance. Store in a desiccator until
used.
3. Lightly grind the sample with a mortar and pestle until it is
able to pass through a
100-mesh sieve screen. Store it in a desiccator until it is
weighed.
4. Using an analytical balance, weigh the sample to the nearest
0.0001 g into a tared
250-mL beaker. When testing with 15% HCl use a glass beaker; for
HCl and HF, use a
plastic beaker.
5. Add approximately 5 mL of methanol to the sample to promote
wetting of the entire
sample and add 100 mL of the acid or acid mixture. Cover the
beaker with a watch glass
or plastic lid.
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Gravimetric Solubility225.020
Analytical Procedures Analytical & Materials QC
January 1999____ Page 2.5-8 Global Laboratory Best Practices,
Vol. 2
7. Remove the beaker from the water bath and filter the sample
with the dried and weighed
Nalgene assembly (see Step 1) connected to a vacuum line through
a trap.
8. Rinse the beaker with up to 50 mL of D.I. water or until all
the residue has been trans-
ferred to the filter. When filtration is complete, detach the
filter from the vacuum and
pour the filtrate back into the beaker for disposal or
additional testing. The filtrate may
be used to determine the percentage of soluble iron.
9. Dry the filter and filtered sample in a vacuum oven at 65C
(150F) for at least 4 hours.
Leave the oven vent valve open slightly to allow airflow through
the oven and to prevent
condensation.
10. Transfer the dry filter and residue to the desiccator and
allow to cool to room tempera-
ture.
11. Weight the filter and residue to the nearest 0.0001 g.
Data Interpretation
Use the following equation to calculate the gravimetric
solubility from the initial sample
weight (Step 6), filter weight (Step 4), and the combined filter
and insoluble residue weight
(Step 13):
References
1. Evaluation of Sand Solubility in Acid,RP 56, Recommended
Practices for Testing
Sand Used in Hydraulic Fracturing Operations, API, Section 6
(1983).
2. Evaluation of Sand Solubility in Acid,RP 58, Recommended
Practices for Testing
Sand Used in Gravel Packing Operations, API, Section 6
(1986).
3. Acid Solubility Considerations,RP 60, Recommended Practice
for Testing High
Strength Proppants Used in Hydraulic Fracturing Operations, API,
Section 6 (1989).
100wtsample
filterresiduefilter1solubleweight%
wtwt
+=
