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.

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.