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boiling when 
operating above 2l2°F. The area of the filter paper 
used in the high-temperature high-pressure (HTHP) 
filter press is one-half the area of the standard filter 
press~ Thus, the volume of filtrate collected in 30 min 
must be doubled before reporting as API water loss. 
An example HTHP filter press is shown in Fig. 2.11. 
I 
DRILLING FLUIDS 
Fig. 2.11-HTHP filter press. 
Example 2.3. Using the following data obtained 
using an HTHP filter press, determine the spurt loss 
and API water loss. 
Time 
(min) 
1.0 
7.5 
Filtrate Volume 
(cm 3) 
6.5 
I4.2 
Solution. The spurt loss of the cell can be obtained by 
extrapolating to zero time using the two data points 
given: 
6.5- I4.2-6.5 .!1 3 ~ _11 vi = 2.07 em 
'Y I .5 - vI 
However, since the standard API filter press has 
twice the cross-sectional area of the HTHP filter 
press, the corrected spurt loss is 4.I4 em 3 . The 30-
min filtrate volume can be computed using Eq. 2.8: 
V3o 2(V7.s-Vsp)+Vsp 
2(14.2- 2.07) + 2.07 = 26.33 em 3 
Adjusting for the effect of filter press cross-sectional 
area, we obtain an API water loss of 52.66 em 3 at the 
elevated temperature and pressure of the test. 
47 
Fig. 2.12-Titration apparatus. 
Both low-temperature and high-pressure API filter 
presses are operated under static conditions - that 
is, the mud is not flowing past the cake as filtration 
takes place. Other presses have been designed to 
model more accurately the filtration process wherein 
mud is flowed past the cake, as it does in the 
wellbore. Such presses that model dynamic filtration 
have shown that after a given period of time the 
mudcake thickness remains constant - that is, the 
cake is eroded as fast as it is being deposited. Thus. 
dynamic-filtration rates are higher than static filtration 
rates. With a constant thickness cake, integrating Eq. 
2.5, we have 
kA tJ.pt 
v1 = -~ . . ..................... (2.9) ll hmc 
A standard dynamic filtration test has not been 
developed to date. Field mud testing uses the static 
filtration test to characterize the filtration quality of 
the mud. Unfortunately, there are no reliable 
guidelines for correlating static and dynamic 
filtration rates. Our ability to predict quantitatively 
filtration rates in the wellbore during various drilling 
operations remains questionable. 
2.1.6 Chemical Analysis. Standard chemical analyses 
have been developed for determining the con-
centration of various ions present in the mud. Tests 
for the concentration of OH- , Cl- , and Ca + + are 
• 
48 APPLIED DRILLING ENGINEERING 
TABLE 2.2-INTERNATIONAL ATOMIC TABLE 
Atomic Atomic 
Element Symbol Number Weight Valence 
ACTINIUM Ac 89 227.0 
ALUMINUM AI 13 26.97 3 
ANTIMONY Sb 51 121.76 3,5 
ARGON A 18 39.944 0 
ARSENIC As 33 74.91 3,5 
BARIUM Ba 56 137.36 2 
BERYLLIUM Be 4 9.02 2 
BISMUTH Bi 83 209.00 3,5 
BORON B 5 10.82 3 
BROMINE Br 35 79.916 1,3,5,7 
CADMIUM Cd 48 112.41 2 
CALCIUM Ca 20 40.08 2 
CARBON c 6 12.01 2,4 
CERIUM Ce 58 140.13 3,4 
CESIUM Cs 55 132.91 1 
CHLORINE Cl 17 35.457 1,3,5,7 
CHROMIUM Cr 24 52.01 2,3,6 
COBALT Co 27 58.94 2,3 
COLUMBIUM Cb 41 92.91 3,5 
COPPER Cu 29 63.57 1,2 
DYSPROSIUM Dy 66 162.46 3 
ERBIUM Er 68 167.2 3 
EUROPIUM Eu 63 152.0 2,3 
FLUORINE F 9 19.000 1 
GADOLINIUM Gd 64 156.9 3 
GALLIUM Ga 31 69.72 2,3 
GERMANIUM Ge 32 72.60 4 
GOLD Au 79 197.2 1,3 
HAFNIUM HI 72 178.6 4 
HELIUM He 2 4.003 0 
HOLMIUM Hd 67 164.94 3 
HYDROGEN H 1 1.0080 1 
INDIUM In 49 104.76 3 
IODINE I 53 126.92 1,3,5,7 
IRIDIUM lr 77 193.1 3,4 
IRON Fe 26 55.85 2,3 
KRYPTON Kr 36 83.7 0 
LANTHANUM La 57 138.92 3 
LEAD Pb 82 207.21 2,4 
LITHIUM Li 3 6.940 1 
LUTECIUM Lu 71 174.99 3 
MAGNESIUM Mg 12 24.32 2 
MANGANESE Mn 25 54.93 2,3,4,6,7 
MASURIUM Ma 43 
MERCURY Hg 80 200.61 1,2 
required to complete the API drilling mud report 
form. A titration apparatus used to perform these 
tests is shown in Fig. 2.12. 
Titration involves the reaction of a known volume 
of sample with a standard solution of known volume 
and concentration. The concentration of the ion 
being tested then can be determined from a 
knowledge of the chemical reaction taking place. 
Several terms used to describe the concentration of a 
given substance in solution are (1) molality - the 
number of gram-moles of solute per kilogram of 
solvent, (2) molarity - the number of gram-moles of 
solute per liter of solution, (3) normality - the 
number of gram equivalents of the solute per liter of 
solution [one gram equivalent weight (gew) is the 
weight of the substance that would react with one 
gram-mole of hydrogen], (4) parts per million (ppm) 
- the number of grams of solute per million grams 
of solution, (5) milligrams per liter - the number of 
milligrams of solute per liter of solution, and (6) 
percent by weight - the number of grams of solute 
per 100 grams of solution. 
Atom1c Atomic 
Element Symbol Number Weight Valence 
MOLYBDENUM Mo 42 95.95 3,4,6 
NEODYMIUM Nd 60 144.27 3 
NEON Ne 10 20.183 0 
NICKEL Ni 28 58.69 2,3 
NITROGEN N 7 14.008 3,5 
OSMIUM Os 76 190.2 2,3,4,8 
OXYGEN 0 8 16.000 2 
PALLADIUM Pd 46 106.7 2,4 
PHOSPHORUS p 15 30.98 3,5 
PLATINUM Pt 78 195.23 2,4 
POLONIUM Po 84 210.0 
POTASSIUM K 19 39.096 1 
PRASEODYMIUM Pr 59 140.92 3 
PROTOACTINIUM Pa 91 231.0 
RADIUM Ra 88 226.05 2 
RADON Rn 86 222.0 0 
RHENIUM Re 75 186.31 
RHODIUM Rh 45 102.91 3 
RUBIDIUM Rb 37 85.48 1 
RUTHENIUM Ru 44 101.7 3,4,6,8 
SAMARIUM Sm, Sa 62 150.43 3 
SCANDIUM Sc 21 45.10 3 
SELENIUM Se 34 78.96 2,4,6 
SILICON Si 14 28.06 4 
SILVER Ag 47 107.880 1 
SODIUM Na 11 22.997 1 
STRONTIUM Sr 38 87.63 2 
SULFUR s 16 32.06 2,4,6 
TANTALUM Ta 73 180.88 5 
TELLURIUM Te 52 127.61 2,4,6 
TERBIUM Tb 65 159.2 3 
THALLIUM Tl 81 204.39 1,3 
THORIUM Th 90 232.12 4 
THULIUM Tm 69 169.4 3 
TIN Sn 50 118.70 2,4 
TITANIUM Ti 22 47.90 3,4 
TUNGSTEN w 74 183.92 6 
URANIUM u 92 238.07 4,6 
VANADIUM v 23 50.95 3,5 
VIRGINIUM Vi 87 224.0 1 
XENON Xe 54 131.3 0 
YTTERBIUM Yb 70 173.04 3 
YTTRIUM Yt 39 88.92 3 
ZINC Zn 30 65.38 2 
ZIRCONIUM Zr 40 91.22 4 
It is unfortunate that so many terms are used to 
express concentration. It is even more unfortunate 
that some of the terms are used inconsistently by 
many people in the petroleum industry. For example, 
the term parts per million sometimes is used in-
terchangeably with milligrams per liter, even at high 
concentrations. 
Example 2.4. A CaC1 2 solution is prepared at 68°F 
by adding 11.11 g of CaC12 to 100 em of water. At 
this temperature, water has a density of 0.9982 
g/cm 3 and the resulting solution has a density of 
1.0835 g/cm 3 . Express the concentration of the 
solution using (1) molality, (2) molarity, (3) nor-
mality, (4) parts per million, (5) milligrams per liter, 
and (6) percent by weight. 
Solution. The molecular weight of Ca and Cl are 
shown to be 40.08 and 35.457, respectively, in Table 
2.2. Thus, the molecular weight of CaC1 2 is 
40.08 + 2(35.457) = Ill. 
• 
DRILLING FLUIDS 
1. For a water density of 0.9982 g/cm3, the molality 
of the solution is 
11.11 g 1 g mol 1 ,000 g 
----------~----~~x ----- x -----(0.9982g/cm3)(100cm3) 111g kg 
= 1.003 g mol/kg. 
The volume of the solution can be computed from 
the mass of solute and solvent and the density of the 
solution. Since 11.11 g of CaCl2 added to 100 g of 
water gave a solution density of 1.0835 g/cm3, the 
solution volume is 
(II. II+ 99.82)g 3 
= 102.38 em 1.0835 g/cm 3 
2. Thus, the molarity of the solution is 
ll.llg lgmol 1,000cm3 
X X 
102.38cm 3 lllg IL 
= 0. 978 g mol/L. 
3. Since 0.5 mol of CaCl 2 would tend to react with 1 
mol of hydrogen, the gram-equivalent weight of 
CaCl 2 is half the molecular weight. The normality of 
the solution is