1. Learn the meaning of the following words, word-combinations and word groups:

treatment, provoke, resilient, segregate, flocculate, dispersion, hamper, peptization, cellulose, derivative, ether, dissociate, decompose, expenditure, saturate, viscidity, viscosity, garments, goggles, wettability, vitreous, froth, foam, suppressor, surfactant, impede, rubber, caoutchouc, kerosene, volatile, friction, wearout, torque, moderate.

2. Read Text 1: Text 1

In the course of drilling solid particles of drilled-out rocks enter the mud fluid, these particles not infrequently containing water- soluble components as well as mineralized and fresh formation waters. A higher ions proportion and a change in the qualitative (saline) composition of the liquid medium provoke, as a rule, coagulation of the mud fluid, attended by growing filtration losses, funnel viscosity, gel strength and by a modification of a number of resilient properties. At times, the influence of mineralization may be so strong that the colloidal particles become completely devoid of the electric charge and hydration envelopes; they agglutinate and form sizable aggregates, while the drilling fluid segregates (flocculates).

To protect the mud fluid against the coagulative action of salts, special chemical substances are added to it. The chemical treatment is also resorted to raise the hydrophilic property of the clays and facilitate their dispersion in water, or else reduce the hydrophility and hamper their peptization. This is also done in order to improve the flowability of the solution, cut down hydraulic resistances during circulation, intensify hydrophilic coagulation, niise viscosity and gel strength, reduce corrosive activity, or impart special properties to the drilling fluid.

The range of chemical reagents used in the treatment of drilling fluids is fairly wide. On adding any of them liable to change are, as a rule, not a single but several properties of the mud fluid; the degree of such changes is dissimilar, while one or two properties undergo quite a substantial change, that of others is rather immaterial. For this reason, quite frequently chemical reagents are conventionally classified into water loss, viscosity and pH control agents, this depending on which of the mud properties undergoes the greatest change under their effect.

The extent to which the properties of the; mud fluid change on introduction of the agent is influenced not only by its composition and concentration, but also by the mineralogical composition of the clay, by that of its exchange complex, by the degree of the dispersion medium (water) mineralization and the composition of its ions, by the concentration of the solid phase , by the temperature, as well as by other factors.

Below are considered in brief the basic groups of chemical agents that have found broadest application in the oil fields.

Cellulose derivatives. To this group belong water soluble varieties of cellulose (cellulose ethers), carboxymethyl cellulose (CMC), sulphoethcr cellulose (SEC), ethane sulphonate cellulose (ESC). Most widely used is carboxymethyl cellulose of different grades.

Carboxymethyl cellulose. The sodium salt of carboxymethyl cellulose is a high- molecular powder-like agent of a white or cream colour, readily soluble in water. In water it dissociates into a sodium cation and a large anion-active radical. In treating drilling fluids several brands of CMC, differing largely in the degree of their polymerization, are used.

CMC-250 is used in treating fresh water and low-salinity weighted-mud fluids containing no water-soluble salts of calcium and magnesium. The thermal stability limit is at about 100°C. At a higher temperature the agent decomposes (thermal oxidative destruction) and its expenditure for the treatment of the mud steeply increases.

CMC-350 is intended for the treatment of drilling fluids of medium salinity, containing not more than 0.2-0.3 per cent of calcium and magnesium salts. Depending upon the temperature and mineralization, the optimal addition during the primary treatment is 1.5-2.5 per cent, and in subsequent treatments, 0.8-1.2 percent. Its thermal stability limit stands at about 130°C.

CMC-500 serves the purpose of reducing the water loss of highly mineralized drilling fluids, including those containing large amounts of calcium salts. Its expenditure for treatment of the mud depends to a still higher degree on pH than does that of CMC with a lesser extent of polymerization. Its thermal stability limit is 150-160 °C.

CMC-600 is designed to push down the filtration losses of highly saline mud fluids. It is especially effective in stabilizing muds saturated with NaCl and used for drilling in deeply occurring deposits of rock salt, as well as in stabilizing highly calcic, gypsum and low- silicate fluids employed for drilling in thick strata of unstable argillaceous rocks.

It is recommended that the sodium CMC agents be introduced into the drilling fluid without their preliminary dissolution in water.

Caustic soda NaOH is a colourless crystalline mass, readily soluble in water. It is used, in the main, for preparation of alkaline agents and also for raising pH of the drilling fluid and limiting the solubility of lime in lime-base muds. Small additives (up to 0.1-0.3 per cent) improve dispersity of clay particles, raise the electrokinetic potential and, hence, reduce viscidity and water loss of mud fluids, Considerable additions of NaOH may cause coagulation of the fluid, this being attended by growing funnel viscosity and filtration loss.

Caustic soda is poisonous, it causes burns on the body surface and blindness, when it gets into the eyes. Its handling is allowed only with protective garments and goggles.

Soda ash NaiCOs is a white-coloured powder, difficultly soluble in cold water, but with rising temperature its solubility improves. It is largely used for combining ions of calcium and magnesium that get into the mud fluid together with the drilled-oui rock and brine, and also to improve the wettability of clay during preparation of muds, the water loss and funnel viscosity being thus forced down. In the absence of NaOH the soda ash is also employed in preparing alkaline agents.

Soluble glass (sodium or potassium silicate) is a vitreous mass of an unstable composition, readily soluble in water. In drilling are used compounds with a modulus SiOi/NaiO = 2.4-3. The agent is designed for increasing the gel strength and funnel viscosity of mud fluids and for raising heat resistance (with an addition of 2-5 per cent) of drilling fluids treated with CMC.

Phosphates (sodium hexametaphosphate, tri-sodium phosphate, sodium pyrophosphate, etc.) serve, in the main, to bind calcium and magnesium ions and to improve the wettability of clays at temperatures of up to 100-120 °C, funnel viscosity and gel strength of fresh-water muds then going down. The effect of the agents is of a comparatively short duration.

Chromates and bichromates serve the purpose of raising normal stability of drilling fluids treated with stabilizing agents and of bringing down viscidity at elevated (roughly above 70 °C) temperatures. The optimal addition should comprise tenths and even hundredths parts of one percent.

They are not recommended for introduction into mud fluid stabilized with water-soluble cellulose ethers.

Chromates are poisonous and should be handled only by wearing protective garments and goggles.

Froth breakers (foam suppressors). To avert foaming of the drilling fluid during its chemical treatment special surfactants capable of impeding the development of a durable froth or effectively attacking it, are added to it. There are available many types of foam suppressing agents, but none of them are of a universal nature. Therefore, it is by experience and experimentation that an effective froth breaker should be chosen to suit conditions prevailing at a concrete well.

Effective froth breakers consist of 10% suspensions of rubber from butadiene and natural caoutchouc and also the ones of polyethylene dissolved in the solar oil or kerosene.

It should be borne in mind that some foam suppressors are toxic (fusel oils, for example), thermally unstable or volatile at elevated temperatures.

Lubricating additives are intended to reduce the coefficient of friction and to keep down the: intensity of the rock-breaking tools wearout (of the bit bearings, above all) and that of drill pipes and also to lower the torque requireel for overcoming the frictional drags to which the drilling string is generally exposed in rotary drilling, as well as to moderate sticking of the string to the borehole walls when operating with bottom drive engines.

Some of the agents discussed above possess lubricating properties (CMC, SEC, starch). Others, however, are not only devoid of such properties, but even contribute to the formation of filter cakes with a higher coefficient of friction.

The best 'effect is achieved with a joint application of the lubricating additive and graphite.