Water-base Drilling Fluids

Water-based drilling fluids, regardless of the name assigned to them, usually contain clays, water soluble chemicals (including salts), a pH control additive (hydroxyl source), and one or more organic polymers, surfactants, and deflocculants.

In order for drilling fluid engineering to be a science and not an art, a basic understanding of the chemistry involved is required. This chapter attempts to provide the chemical background to the reactions that take place in the fluid.

By adoption of this approach the engineer will be well equipped to deal with variations in the fluid properties which may occur from time to time. If the basic chemical concepts are well understood, then the causes of any problems can be better identified and dealt with.

The Structure of Matter

The properties and reactions of materials can be related to the basic structures of the atoms and molecules of which they are formed. The difference between water and diesel, bentonite and sand, and so on, arises from their physical and chemical properties which are best understood in these terms.

Vortex formation in fluid

Elements and Compounds

An element is a chemically unique substance which cannot be split up into a simpler chemical form by chemical means. The names of the various elements are usually written as abbreviations to simplify chemical notation. A full list of elements and their symbols is given in Table 1.

Table 1. Known Elements and Atomic Weights

Element Symbol Atomic Number Atomic Weight Element Symbol Atomic Number Atomic Weight
Actinium Ac 89 227* Mercury Hg 80 200.59
Aluminum Al 13 26.9815 Molybdenum Mo 42 95.94
Americum Am 95 243* Neodymium Nd 60 144.24
Antimony Sb 51 121.75 Neon Ne 10 20.179
Argon Ar 18 39.948 Neptunium Np 93 237.0482
Arsenic As 33 74.9216 Nickel Ni 28 58.71
Astaline At 85 210* Niobium Nb 93 237.0482
Barium Ba 56 137.33 Nitrogen N 7 14.0067
Berkelium Bk 97 247* Nobelium No 102 259*
Beryllium Be 4 9.01218 Osmium Os 76 190.2
Bismuth Bib 83 208.9808 Oxygen O 8 15.9994
Boron B 5 10.81 Palladium Pd 46 106.4
Bromine Br 35 79.904 Phosphorus P 15 30.9738
Cadmium Cd 48 112.41 Platinum Pt 78 195.09
Caesium Cs 55 132.9054 Plutonium Pu 94 244*
Calcium Ca 20 40.08 Polonium Po 84 209*
Californium Cf 98 251* Potassium K 19 39.0983
Carbon C 6 12.011 Praseodymium Pr 59 140.9077
Cerium Ce 58 140.12 Promethium Pm 61 145*
Chlorine Cl 17 35.453 Protactinium Pa 91 231.0359
Chromium Cr 24 51.996 Radium Ra 88 226.0254
Cobalt Co 27 58.9332 Radon Rn 86 222*
Copper Cu 29 63.546 Rhenium Re 75 186.2
Curium Cm 96 247* Rhodium Rh 45 102.9055
Dysprosium Dy 66 162.50 Rubidium Rb 37 85.467
Einsteinium Es 99 254* Ruthenium Ru 44 101.07
Erbium Er 68 167.26 Samarium Sm 62 150.4
Europium Eu 63 151.96 Scandium Sc 21 44.9559
Fermium Fm 100 257* Selenium Se 34 78.96
Fluorine F 9 18.9984 Silicon Si 14 28.0855
Francium Fr 87 223* Silver Ag 47 107.868
Gadolinium Gd 64 157.25 Sodium Na 11 22.9898
Gallium Ga 31 69.72 Strontium Sr 38 87.62
Germanium Ge 32 72.59 Sulphur S 16 32.06
Gold Au 79 196.9665 Tantaium Ta 73 180.9479
Hafnium Hf 72 178.49 Technetium Tc 43 98.9062
Helium He 2 4.0026 Tellurium Te 52 127.60
Holmium Ho 67 164.9304 Terbium Tb 65 158.9254
Hydrogen H 1 1.0079 Thalliium Tl 81 204.37
Indium In 49 114.82 Thorium Th 90 232.0381
Iodine I 53 126.9045 Thulium Tm 69 168.9342
Iridium Ir 77 192.22 Tin Sn 50 118.69
Iron FE 26 55.847 Titanium Ti 81 204.37
Krypton Kr 36 83.80 Tungsten W 74 183.65
Lanthanum La 57 138.9055 Uranium U 92 238.029
Lawrencium Lr 103 260* Vanadium V 23 50.941
Lead Pb 82 207.2 Xenon Xe 54 131.30
Lithium Li 3 6.941 Ytterbium Yb 70 173.04
Lutetium Lu 71 174.97 Yttrium Y 39 88.9059
Magnesium Mg 12 24.305 Zinc Zn 30 65.38
Manganese Mn 25 54.9308 Zirconium Zr 40 91.22
Mendelevium Md 101 258*

Atomic weights quoted are the 1969 values based on carbon 12 and include the IUPAC revision 1971 Values marked * are for the most stable or most common isotopes.

Elements can combine together to form compounds. A compound has different chemical and physical properties than those of the simple mixture of elements from which the compound is formed. Thus hydrogen and oxygen are both gases and remain gases when they are mixed together. However, if they are chemically combined, they form water, which is a liquid. When elements combine together, they do so in a fixed ratio by weight, which always remains constant for one particular compound.

Atoms and Molecules

An atom is the smallest particle of an element which can exist and still retain the same chemical properties of that element. Atoms are the basic building bricks of matter from which all things are constructed. They are the smallest units of matter which can undergo chemical change.

A molecule is the smallest particle of a compound which can exist and still retain the same chemical properties of that compound. Molecules consist of atoms chemically bonded together in a precise arrangement. A molecule of water consists of two atoms of hydrogen combined with one atom of oxygen to give a chemical formula of H2O. When the elements hydrogen and oxygen combine to form the compound water, each molecule of water consists of two atoms of hydrogen bonded to one atom of oxygen.

 

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