Thus, it is expedient that water in its capacity of a drilling fluid is to be used in drilling off of stable and sufficiently firm rocks of unproducing horizons whose mechanical properties remain virtually unchanged on their humidification, whereas an aqueous solution of NaCl should be employed in drilling out halite deposits in the presence of abundant sources of water supply, i.e. when disadvantages inherent in brine (because of its dilution) cannot materially affect proper sinking and cost of the well, while utilization of other drilling fluids can adversely influence the effectiveness of drilling.
3 Find in Text 1 five sentences with non-finite forms of the verb, define their functions and translate the sentences into Ukrainian.
4 Write 8-10 questions covering the main idea of Text 1.
5 Explain why water is not a universal drilling fluid.
6 Read Text 2:
Text 2 Mud Fluids
The requirements which mud fluids must satisfy under difficult geological conditions can be met only by employing a multicomponent system with adjustable composition and properties. In a geological situation where there is a need for a drilling fluid with a density of 1000 kg/m3 and more, such a system should be composed of the following components:
a) readily available liquid medium as its base at a price as cheap as possible;
b) a small bulk of colloidal particles sufficient to provide for a sedimentational stability of the system at rest due to its transformation into a gel and capable of plugging up pores and fine fractures in rocks;
c) a minimum amount of finely ground heavy minerals, to ensure a preassigned density of the system;
d) a small quantity of chemical reagents for regulating physico-mechanical and chemical properties of the system and for protecting it against adverse effects, of the environment (formation brines and gases, dri!led-out rock, temperature, etc.).
In nature a most abundant and cheap source of colloidal materials are certain varieties of clay. The multicomponent drilling fluids where such clays are used as colloidal fractions have been given the name of mud fluids or slurries.
The earth's crust contains a large number of argillaceous minerals which, except for rare cases, have a crystalline texture. These minerals differ both in their chemical composition and crystal lattice structure. As regards their composition the clayey minerals are alumosilicates.
Crystalline argillaceous minerals are subdivided into double- layer, triple-layer, true mixed-layered and the ones with a chain structure. For the preparation of drilling solutions of major importance are triple-layer minerals of the montmorillonite group and the ones of the palygorskite group with the chain structure. The principal structural element in the crystal lattice of the montmorillonite group minerals is pyrophyllite - a hydrous silicate with chemical composition AliCbxTSiOixF^O. The unit cell of its crystal lattice is of an extremely small thickness (I0~(’ mm) and consists of three layers or blankets. The upper and lower layers are formed of SiC>2 tetrahedrons, while the middle layer, bonding the outer ones, is made up of alumoxygenous-hydroxy] i с octahedrons AI2O3X11H2C).
In choosing the variety of clay for preparation of a mud fluid of essential importance is mineralization (salt content) of water of mixing and the composition of rocks to be drilled out. If there is no risk of any substantial mineralization of the mud fluid under the effect of the drilled-out rock fragments, formation brines and gases that get into it in the course of drilling, the best source of the colloidal fraction will then be bentonite. Because of a low-strength oxygen bonds between the montmorillinite scales and a high degree of dispersion the bentonite is apt to break into unit scales in fresh water, to swell and combine physically г. large amount of water. Especially prone to an intensive bulking up are sodium bentonites; a pellet of such a clay when breaking up in fresh water can increase in volume by as much as 8 to 14 times. Much less susceptible to swelling are calcic and magnesia bentonites. With diminishing proportion of montmorillinite in the clay the extent of its swelling decreases and a much greater amount of the clayey material is needed to prepare a stable suspension.
7 Make a written translation of the following:
In nature a most abundant and cheap source of colloidal materials are certain varieties of clay. The multicomponent drilling fluids where such clay s are used as colloidal fractions have been given the name of mud fluids or slurries.
The earth's crust contains a large number of argillaceous minerals which, except for rare cases, have a crystalline texture. These minerals differ both in their chemical composition and crystal lattice structure. As regards their composition the clayey minerals are alurnosilicates.
8 Make a plan to Text 2 and retell it.
9 Read Text 3:
Text 3 Drilling Fluid with Magnesium Hydrogel as Its Base
In drilling out chemogenic deposits water-soluble particles of sodium, potassium, magnesium chlorides and also of calcium sulphates enter the mud fluid. Investigations have shown that concentrated multi-component brines with high proportion of magnesium can be transformed into sedimentation-stable systems capable at rest to carry suspended particles of drilled-out rocks. On treating such a brine with alkali NaOH or Ca(OH)2 there develops a structurized system, known conventionally as magnesium hydrogel, which contains colloidal particles of magnesium oxychlorides, along with calcium sulphates and carbonates, as well as of other compounds and displays thixotropic properties. This type of drilling fluid may be used effectively in piercing chemogenic strata, intersaline and sometimes also subsaline deposits.
10 Write a summary of the Te xt 3.
11 Read Text 4 without a dictionary and retell it in Ukrainian: Text 4 Natu ral Aqueous Suspension
In traversing nonargillaceous rocks (carbonaceous, sulphate, aleurolite) and argillites, the drilling fluid receives a certain quantity of finely dispersed solid particles and very few colloidal ones. With water used as drilling fluid, the developing aqueous suspension of drilled-out particles appears sedimentally unstable; it is devoid of the solids-carrying capacity at rest. A positi ce quality of such a suspension is the low sensitivity of the dispersed phase to the coagulating action of salts. Therefore, efforts are made in a number of cases to stabilize the naturally formed aqueous suspension of finally dispersed particles of the drilled-out rocks through introduction into it of certain structure-forming chemical reagents (starch, carboxymethyl-cellulose, humate agents, sulphate cellulose, etc.) and sometimes also a small amount of high-quality montmorillinite clay.
12 Give English equivalents of the following:
аномалія, мікротріщина, турбулентний, виймання, бригада, недолік, обмежувати, впливати, зволожений стан, порода із тріщинами, припиняти, бурова колона, занести мулом, осад,
галіт, вибурені шматки, глинисті частинки, навколишнє середовище, колоїдна фракція, стабільна суспензія, у стані
спокою, при обробці, розбурювання, бути позбавленим чогось, коагулюючи дія.
Unit 10 Chemical Agents for the Treatment of Water-Base Drilling Fluids
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, raise 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 10Q°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 bums on the body surface and blindness, when it gets into the eyes. Its handling is allowed only with protective gannents and goggles.
Soda ash Na2C03 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-out 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 required 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 1o 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.
3 Supply a heading for Text 1.
4 Make a plan to Text 1.
5 Speak about the basic groups of chemical agents that have found the broadest a pplication in the oil field.
6 Translate the following sentences into English using the words and expressions from Text I.
1) Для захисту промивальної рідини від дії солей до неї додають спеціальні хімічні речовини.
2) Асортимент хімічних реагентів, що застосовуються для обробки промивальних рідин, досить широкий.
3) Гіри більш високій температурі препарат розкладається і витрата його на обробку розчину різко зростають.
4) Каустична сода отруйна, викликає опіки тіла, а при попаданні в очі - сліпоту.
5) Працювати з цими речовинами слід у захисному одязі та захисних окулярах.
7 Find in Text 1 five sentences with Passive Voice forms of the verb and translate the sentences into Ukrainian.
8 Give English equ ivalents of the following:
промивальна рідина, що має водну основу, гідратна оболонка, випадати пластами, катіон натрію, межа термостійкості, оптимальна добавка, водовіддача, лужний реагент, захисний одяг, захисні окуляри, кальцинована сода, рідке скло, піногасник,
каучук, солярова олива, сивушні масла, змащувальна добавка, породоруйнуючий інструмент, підшипник долота, опір тертя, бурильна колона, зависання колони, стінка свердловини, привідний глибинний двигун, осад після фільтрування.
Unit 11
Chemical Treatment of Water-Base Drilling Fluids
1 Learn the meaning of the following words;, word-combinations and word groups:
adjust, preclude, excess, traverse, suppress, swelling, inhibition, alkalinity, decompose, augment, piercing, defer, dense, thinner, starch, hazard, thickening, solidification, at rest, condense, investigation, humidification, implication, consumption.
2 Read Text 1:
Text 1 Chemical Treatment of Water-Base Drilling Fluids
The properties of the mud fluid undergo changes in the course of drilling. Depending upon the cause producing the change, the method of adjusting or stabilizing its properties is chosen.
One of the causes is a higher concentration of finely dispersed solid (particularly clayey) phase, attended by growing viscidity, gel strength and, to a lesser degree, density of the mud fluid. To preclude an intensive rise of viscidity it is advisable to keep an eye on the concentration of the solid phase and to regularly remove all of its excess, so as to maintain the preset density and gel strength. If it proved to be insufficient, a reagent - thinner is added to the drilling fluid. When traversing thick clayey strata the dispersing medium of the drilling fluid should be given the faculty of suppressing the tendency of the drilled-out clayey particles towards peptization and swelling in water. Mud fluids which display such an ability are conventionally called inhibited and the treatment for creating the faculty to suppress peptization is termed inhibition.
Another cause responsible for changes in the properties of the drilling fluid is its coagulation under the effect of water-soluble salts coming in together with the drilled-out rock and of salts contained in formation fluids. Coagulation is accompanied by an increased water loss, growing gel strength and funnel viscosity. Depending upon the concentration of salts and the valence of ions, the complexity of the chemical treatment varies rather significantly.
The third cause is changed alkalinity of the mud fluid because of its mineralization. Therefore, in order to keep up the pre-assigned properties of a chemically treated drilling fluid it is important to maintain a range of pH optimal for a given water-loss control agent, or thinner, by adding caustic (or calcined) soda or lime to some inhibited fluids.
The fourth cause is rising temperature of the mud fluid that mounts as the well gets deeper. The increase of the temperature is attended, as a rule, by growing gel strength, falling plastic viscidity of the mud and dynamic viscidity of its filtrate, parallelled by a mounting water loss. At high temperatures some agents may decompose. Therefore, with growing temperature it may become necessary to replace some less thermally stable reagents with other more heat resistant ones, or to introduce an additional agent capable of augmenting the thermal stability of the primary substances with which the mud has been treated.
In piercing thick strata of argillaceous rocks, or alternating i layers of clayey and chemogenic ones a good effect is accomplished by using inhibited drilling fluids. It is basically water-soluble calcium salts and calcium hydroxide, which act as coagulants on the clays, that are employed in the capacity of inhibiting agents and which strongly defer peptization and swelling of clay particles of the drilled out rock in a dispersion medium of mud. Since coagulation is followed by rising water loss, funnel viscosity and gel strength, water- loss control agents and thinners have to be added to the mud fluid, along with the inhibiting agent. With such a combined treatment a material increase in proportion of the solid phase does not produce so very intensive growth of viscidity as is seen to occur in uninhibited mud fluids. This is of prime importance, particularly in cases when a highly dense mud is required for drilling.
The following are the varieties of inhibited mud fluids employed in the field.
1 Lime-base ones, where as an inhibiting agent figures lime, and thinners are represented by lignosulphonates, polyphenols, or
oxidated lignines, while among water-loss control agents are starch and CMC. Such fluids present satisfactory filtration properties at pH > 12 and calcium ions content in the filtrate of not more than 300 g/nr3, while muds with a low level of the clayey phase are suitable at pH > 10.5.
As a rule, lime-base muds are not recommendable at temperatures exceeding 100-120 °С, for then a sharply increased filtration loss and a hazard of thickening and even solidification at rest, especially in cases of an elevated content of finely dispersed clays, are to be reckoned with.
2 Gypsum-base muds, where an inhibiting agent is calcium sulphate (whose source are gypsum, alabaster or anhydrite), a thinner is ferrochromolignosulphonate and a water-loss control agent is CMC and, at temperatures above 180 °С, brown coal treated with chromium compounds. These muds display a stronger inhibiting action than do the lime-base ones, with the calcium cations therein varying from 0.8 to 1.2 kg/m.
The optimal pH value is maintained through addition of alkali.
3 Highly calcic muds, where calcium chloride serves the part of an inhibitor, lignosulphonates and chromolignosulphonates act as thirmers, while the condensed lignosulphonate or starch figure as a water-loss control agent. 'Hie calcium ions content in the filtrate may vary from 0.8 to 5 kg/m3, optimal range of pH being 8 to 10. Caustic soda or lime may be used for adjusting pH. Investigations have demonstrated calcic muds with Ca++ level from 2 to 3 kg/m3, treated with 0.12-0.15 per cent of lime, to be more effective. The filtrate of such a mud greatly slows down the rate of the decline in toughness of argillaceous rocks and argillites on their humidification.
Chlorocalcic muds can be used at temperature of up to 1 ЗОНО °С (depending upon the thermal stability of the water-loss control agent).
4 Barium-base ones, where barium hydroxide acts as an inhibitor and condensed lignosulphonate serves the part of a water- loss control agent. Such muds are distinguished by displaying the strongest inhibitory action.
When choosing the inhibition method one should take account of a possible economic implications, for the cost of some reagents is
fairly high and their consumption quite significant.
The drilling f uid is to be treated with chemical agents only after it has been cleared of drilled-out rock fragments (drilling breaks) and of the excess of the solid phase.
3 Find in Text 1 five sentences with Passive Voice forms of the verb and translate the sentences into Ukrainian.
4 Give English equivalents of the following:
pear ент-поиижувач в’язкості, окислені лігніни, вапняний розчин, гіпсовий розчин, понижувач водовіддачі, оптимальне значення, висококальдієвий розчин, зазнавати змін, у процесі обробки, тонкодясгіерсна тверда фаза, стежити, дисперсійне середовище, під впливом солей, зростання водовіддачі, вибирати спосіб інгібування, уламки вибурених порід.
5 Translate the following sentences into English using the words and expressions from Text 1.
1) Властивості промивальної рідини змінюються в процесі буріння.
2) Хімічну обробку проводять багато разів, періодично додаючи в промивальну рідину нові порції реагентів.
3) Оптимальне значення pH підтримують додаванням
лугу..
4) ГІри виборі способу інгібування слід враховувати можливий економічний ефект, оскільки вартість деяких реагентів висока, а витрати їх значні.
5) ГІри деяких видах комбінованої хімічної обробки має значення послідовність введення реагентів.
6 Make a plan to Text 1.
7 Write ten questions to the text.
8 Speak about the causes responsible for changes in the properties of the drilling fluid.
Unit 12
Density Adjustment of Water-Base Mud Fluids
1 Learn the meaning of the following words, word-combinations and word groups:
shoe, avert, crumbling, caving-in, mill, admixture, sinter, slag, smelt, copper, lead, ore, humid, retard, preliminary, dilute, diminish, surplus, consumption, reclaim.
2 Read Text 1:
Text 1 Density Adjustment of Water-Base Mud Fluids
To preclude the inflow of formation fluids into the well it is necessary that the pressure of the drilling fluid column be somewhat greater than the formation one. For this reason, the density of the mud fluid is chosen with due regard for the coefficients of abnormality in the horizons which will be drilled in the course of advancing along an interval from the shoe of the preceding rasing string to the landing depth of the subsequent casing string.
The density of the drilling fluid must sometimes be increased also in order to avert crumbling or caving-in of unstable rocks.
A more significant increase of the mud density is achieved by addition of special finely ground heavy minerals (weighting materials). Such minerals must have high density and should not be abrasive.
The best weighting material is the one containing barite, obtained through milling of the natural mineral - heavy spar (barium sulphate). The density of pure barium sulphate is as high as 4600 kg/m\ For the needs of drilling commercial grades of barite that contain various admixtures (silica, limestone, dolomite, etc.) are supplied.
Apart from barite wide use have found ferruginous weighting materials, and also slags remaining after smelting of copper and lead ores. These weighting materials are much more abrasive by comparison with barite. Their use is however, favoured by the higher density and, partially, is due to the shortage of barite weighting materials.
The weighting material is added to the drilling fluid in a humid state. To introduce dry weighting material is not recommendable, for air particles adsorbed on hard minerals tend to raise funnel, viscosity and to retard the growth of density. Inasmuch as on add tion of the weighting material funnel viscosity of the drilling fluid increases, it is advisable that the weighting material be preliminarily humidified with an aqueous solution of thinners and water-loss control agents. This enables it to achieve a more intensive rise of density with an insignificant increase of viscidity.
In the course of drilling the viscosity of the weighted drilling fluid gradually increases because of a higher concentration of the solid phase at the expense of fine fractions of the drilling breaks and due to coagulating action of salts. To bring down the viscosity the mud fluid is usually diluted with water and treated with a water-loss control agent and, since the density then diminishes a new portion of the weighting material is added to the mud. This results in that a large surplus of the weighted mud accumulate at the drill rig and the consumption of the weighting material and chemical agents greatly increases.
The consumption of the weighting material and reagents, and also the cost of the treatment, may be significantly reduced if, as the surplus stocks of the mud pile up, the weighting material is being reclaimed therefrom.
3 Find in Text 1 sentences with Modal Verbs and translate them into Ukrainian.
4 Give English equi valents of the following words and use them in the sentences of your own:
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