Supplement Text 1 Mud Fluids

Thanks to unsaturated oxygen valences along the faces and at the apices of the crystal lattice the elementary (unit) scales can join one another lengthwise the crystallographic axis C, and thus form a multilayered aggregate. Since the bonds between the scales are weak, such an aggregate, when agitated in a liquid, i s apt to split easily into unit scales along the stratification planes. The outer layers of the pyrophyllite seales are equiipotential and the scale itself is, therefore, electrically neutral, except for the si tes of the crystal lattice rupture, where there may exist positive and negative charges.

The minerals of the moritmorillinite group differ from pyrophyllite in that the composition of their crystal lattice includes atoms of magnesium, iron, chromium and other elements. These atoms replace, as it were, some atoms of aluminium and silicon, the substitution, as a rule, being equivalent. Some of the trivalent aluminium atoms are replaced unequally, with bivalent magnesium or iron atoms, for example, and some tetravalent silicon atoms with trivalent atoms of aluminium or other elements. With such an unequal substitution, the scale acquires excess negative charges. These charges are balanced by single- or poly-valent cations (of sodium, potassium, calcium, etc.) which, however, do not make part of the crystal lattice, and, being disposed at the outer surface of the silicate layers, are, nevertheless, combined with it by the force of electric interaction. . ,

Should a pellet of montmorillinite be put in an aqueous solution containing, for example, cations of calcium, the substitution reaction between calcium and the atoms making part of the crystal lattice is impossible. But the substitution reaction is possible between calcium and the cations lying at the outer surface of the silicate layers and offseting excess charges of the clayey particle. Such cations are, therefore, called exchange cations, and they compose an exchange capacity of argillaceous minerals and clays. The exchange capacity is commonly characterized by milligram-equivalents of cations adsorbed by the surface of 100 g of an air-dry argillaceous mineral or claiy.

The presence of exchange ions makes an argillaceous mineral active, preconditions many of its important properties, such as the ability to participate in exchange reactions, to undergo ionization, hydration, etc.

Yet another representative of triple-layer argillaceous minerals are hydromicas. In addition to aluminium and silicon atoms, into composition of their crystal lattice enter atoms of iron and magnesium. Trivalent aluminium atoms substitute non- equivalently some of the tetravalent silicon atoms; an excess negative charge that develops at this juncture is balanced by cations of both potassium and other elements. The potassium cations lie on the surface of the crystal lattice and are firmly bound with it. Non- equivalent substitution of atoms in the crystal lattice accounts for the exchange capacity of hydromicas. As concerns their exchange capacity, some hydromicas stand close to the minerals of the montmorillinite group, while others come nearer to the minerals of the kaolinite group. Hydromicas are characterized by a high degree of dispersion.

A typical representative of double-layer minerals is kaolinite. Its unit scale is made up of one silicate and one aluminate layer. A non-equivalent substitution of aluminium or silicon atoms is nearly impossible. Hence, the kaolinite scales are either neutral or have a very insignificant charge, the exchange capacity of such a mineral being extremely small. Between neighbouring scales along crystallographic axis C there exists a strong hydrogen bond of the OH-O type. If a kaolinite pellet be immersed in water then on stirring unlike montmorillinite, it does not split up into unit scales.

To the group of minerals with the chain structure belongs palygorskite. This is an aqueous magnesium alumosilicate. The unit cell of palygorskite consists of twin silico-oxygen chains. The adjacent silicon-oxygen (silicic) tetrahedrons have their apices turned into opposite directions, which makes the chain look like a ribbed blanket. Two adjoining chains are disposed in such way that the apices of the successive layers or blankets face each other, whereas the layers themselves are linked together through the intermediary of alumoxigen octahedrons. In these octahedrons the magnesium and iron atoms serve as substitutes for some of

the aluminium atoms. Because of not quite an equivalent substitution, the palygorskite particles have an excess negative charge The exchange capacities of argillaceous minerals differ quite significantly and lie within the range (in mg-equiv/100 g) for:

Montmorillinite 80-150

ENGLISH FOR OIL AND GAS ENGINEERS 1

Передмова 11

PART 1 13

MECHANICAL PROPERTIES OF ROCKS 13

Unit 1 13

Physical and Mechanical Properties of Rocks 13

The Effect of Three-Dimensional Compression and Temperature on the Mechanical Properties of Rocks 21

Unit 3 25

The Effect of Saturating Fluid on the M echanical Properties of Rocks 25

Abrasiveness of Rocks 28

CONTROL TASKS 32

PART 2 DRILL BITS 34

Unit 5 34

Purpose and! Classification 34

Unit 6 Rroller Bits 37

Unit 7 Diamond - Set Bits 39

CONTROL TASKS 42

PART 3 MUD TECHNOLOGY 45

Unit 8 45

Purpose and Classification of Drilling Fluids 45

Unit 9 48

Water-Base Drilling Fluids 48

Unit 10 53

Chemical Agents for the Treatment of Water-Base Drilling Fluids 53

Chemical Treatment of Water-Base Drilling Fluids 58

Density Adjustment of Water-Base Mud Fluids 62

6 Give a summary of Text 1. 63

7 Speak about density of the drilling fluid and weighting materials. 63

Unit 13 Oil-Base Drilling Fluids 63

1 Learn the meaning of the following words, word-combinations and word groups: 63

2 Read Text 1: 63

Text 1 Oil-Base Drilling Fluids 63

3 Pick out Infinitive and Participle constructions from Text 1 and explain their use. 65

4 G ive English equi valents of the following words and use them in the sentences of your own: 65

5 Translate the following sentences into Ukrainian: 66

6 Divide the text into logically complete parts and give each a subtitle. Put questions to the first part and retell it in English. 66

7 Speak about the properties of the lime-bitumious drilling fluid. 66

Unit 14 Emulsion Muds 67

1 Learn the meaning of the following words, word-combinations and word groups: 67

2 Read Text 1: 67

Text 1 67

3 Pick out Infinitive Constructions from Text 1 and explain their use. 69

4 Give English equivalents of the following words and use them in the sentences of your own: 69

§ Translate the following sentences into Ukrainian: 69

6 Supply a heading for Text 1. 69

7 Read Text 1 again. Find, read and translate the sentences in Text 1 in which we learn about emulsion of the oil in water type, emulsion of the water in oil type, the emulsifier. 69

8 Look through Text 1 again. Give the main points of each passage of the text. Use: "deals with". 69

9 Divide the text into logically complete parts and give each a subtitle. Put questions to the second part and retell it in English. 69

Gaseous Agents and Aerated Drilling Fluids 70

1 Learn the meaning of the following words, word-combinations and word groups: 70

Text 1 Gaseous Agents 70

3 Write ten questions to the text' and answer them. 71

4 Make a plan to Text 1. 71

5 Reproduce Text 1 in your own words according to the plan. 71

Text 2 Aerated Drilling Fluids 71

7 Pick out of Text 1 and Text 2 five sentences containing Passive Voice Constructions and translate them into Ukrainian. 72

8 Give English equivalents of the following words and use them in the sentences of your own: 72

9 Translate Text 2 iitito Ukrainian. 72

10 Give the main points of each passage of Text 1. Use: "deals with". 72

CONTROL TASKS 72

1 Answer the questions: 72

4 Tell whether each of the following statements is true or false according to the text. Correct the false statements to make them true: 74

5 Make a written translation of the following: 74

PART 4 74

DRILLING METHODS AND DRILLING EQUIPMENT 74

Unit 16 Methods of Drilling 74

1 Learn the meaning of the following words, word-combinations and word groups: 74

2 Read and translate Text 1: 75

Text 1 Description of an Oil Well 75

3 Translate the following words and word combinations and use them in the sentences of your own: 76

4 Pick out from Text 1 all the sentences containing Modal Verbs and translate them in to Ukrainian. 76

5 Write 8-10 questions covering the main idea of Text 1. 76

6 Learn the meaning of the following words, word-combinations and word groups : 76

Text 2 Methods of Drilling 76

Drilling by the turbine method. In turbine drilling the bit is 78

8 Find in Text 2 English equivalents for the following: 82

9 Make a written translation of the following: 82

10 Describe in brief each method of drilling. 82

11 Working in pairs test each other's ability to describe 82

advantages and disadvantages of each method of drilling. 82

Unit 17 Drilling Equipment 82

1 Learn the meaning of the following words, word-combinations and word groups: 82

2 Read Text 1: 82

Text 1 Drilling Equipment 82

3 Give English equivalents of the following: 85

4 Pick out from Text 1 all the verbs in the Passive Voice. 86

5 Give definitions of derrick, substructure and drawworks using Text 1. 86

6 Find, read and translate the sentences in Text 1 in which we learn about brakes and mud pumps. 86

7 Working in pairs test each other's ability to describe the main functions of the basic rig components. 86

Unit 18 86

Auxiliary Drilling Equipment 86

1 Learn the meaning of the following words, word-combinations and word groups: 86

2 Read Text 1: 86

3 Make a written translation of the following: 87

1. Make a plan to Text 1 and retell it. 87

2. Learn the meaning of the following words, word-combinations and word groups: 87

3. Read Text 2: 87

Text 2 Casing and Cementing 87

4. Give English equivalents of the following: 89

5. Make a written translation of the following: 89

6. Describe the processes of casing and cementing using Text 2. 89

7. Learn the meaning of the following words, word-combinations and word groups: 89

8. Read Text 3: 89

Text 3 89

13 Put 5 questions to Text 3. 91

14 Find, read and translate the sentences in Text 3 in which we learn about Christmas Tree. 91

15 Learn the meaning of the following words, word-combinations and word groups: 91

16 Read Text 4: 91

Text 4 91

17 Give English equivalents of the following: 93

18 Describe the main fishing tools using Text 4. 93

19 Find, read and translate the sentences in Text 4 in which we learn about directional drilling. 93

JO Read Text 5: 93

Text 5 Offshore Drilling Equipment 93

21 Give English equivalents of t he following: 95

22 Make a written translation of the following: 95

23 Make a plan to Text 5 and retell it. 95

CONTROL TASKS 96

1 Answer the questions: 96

ZGive English equivalents of the following: 96

4 Tell whether each of the following statements is true or false according to the text. Correct the false statements to make them true: 99

5 Make a written translation of the following: 99

P ART 5 100

COMPLICATIONS IN THE COURSE OF DRILLING 100

Unit 19 Circulation Loss 100

1 Learn the meaning of the following words, word-combinations and word groups: 100

2 Read and translat e Text 1: 100

Text 1 Difficulties Encountered in Drilling 100

5 Pick out from Text 2 five sentences containing the verbs in Passive Voice and translate them. 102

6 Make a plan to Text 2 and retell it. 102

7 Learn the meaning of the following words, word-combinations and word groups: 102

8 Read Text 3: 102

Text 3 102

9 Fiind in Text 3 English equivalents for the following: 105

10 Find in Text 3 Infinitive constructions and translate them into Ukrainian. 105

11 Find in Text 3 conditional sentences and translate them into Ukrainian. 105

12 Make a written translation of the following: 105

13 Translate the following sentences into English using the words and expressions from Text 3. 105

14 Supply a heading for Text 3. 106

15 Imagine that you are asked to make a report on measures used for eliminating circulation losses. Write the main points of your report and illustrate each point with the material from Text 3. 106

Unit 20 106

Gas-, Oil-, and Waiter-Showings 106

1 Learn the meaning of the following words, word-combinations and word groups: 106

2 Read and translate Text 1: 106

Text 1 106

3 Find in Text 1 conditional sentences and translate them into Ukrainian. 108

4 Give English equivalents of the f ollowing: 108

5 Make a w ritten translation of the following: 108

6 Supply a heading for Text 1. 109

7 Find,, read a»id translate the sentences in Text 1 in which we learn what to do if it is impossible to preclude the inflow of formation fluids and gas and & blowout occurs. 109

8 Working in pairs test each other's ability to describe measures for preventing the influx of formation fluids and gases into the well. 109

Unit 21 109

Crumbling and Caving-in of Rocks, Narrowing of the 109

Well Bore 109

1 Learn the meaning of the following word?;, word-combinations and word groups: 109

2 Read and translate Text 1: 109

Text 1 Caving and Freezing of the E»rill Column 109

3 Find in Text 1 the sentences containing modal verbs and translate them into Ukrainian. 111

4 Make a written translation of the following: 111

5 Speak about causes of frozen drill pipe. 111

6 Write a summary of Text 1. 111

7 Learn the meaning of the following words, word-combinations and word groups: 111

8 Read Text 2: 111

Text 2 111

9 Translate the following sentences into English using the words and expressions from Text 2. 113

10 Supply a heading for Text 2. 114

11 Divide Text 2 into logically complete parts and give each a subtitle. 114

12 Working in pairs test each other's ability to describe the principal causes of crumbling and caving-in of rocks and narrowing of the well bore. 114

Unit 22 114

Sticking of Drilling and Casing Strings 114

1 Learn the meaning of the following words, word-combinations and word groups: 114

2 Read and translate Text 1: 114

Text 1 114

2 Read and translate Text 1: 116

Text 1 Deep Well Drilling 116

3 Make a written translation of the following: 117

4 Divide Text 1 into logically complete parts and give each a subtitle. 117

5 Put questions to each part of Text 1 and retell it in English. 117

6 Read and translate Text 2: 117

Text 2 Some Perspectives of Drilling Wells up to 15.000 m 117

CONTROL TASKS 120

PART 6 122

DRILLING IN AND TESTING OF PAY BEDS 122

Unit 24 122

Influence of Drilling Fluid on the Collecting Properties 122

of Pay Beds 122

Unit 25 125

The Choice of Mud Fluid for Drilling in the Pay Bed 125

Unit 26 128

Choosing a Metltiod for Opening-up a Reservoir-Bed and an Arrangement of the Area in and around the Hole Face in Producing Wells 128

CONTROL TASKS 131

GLOSSARY 137

REFERENCES 207

In nature argillaceous minerals occur rarely. They usually enter the composition of rocks known as clays. The natural clay is composed of a mixture of several argillaceous minerals and nonargillaceous admixtures, such as, for example, quartz, colloidal silica and others. Clays in whose composition the major part play montmorillinites are called bentonites. When, in addition to montmorillinites, clay contains a significant proportion of hydromicas or kaolinites, it is termed subbentonite. Clays in which kaolinites prevail are called kaolin clays.

Apart from colloidal fractions the natural clay carries large particles which, obviously, affect the density of the clay suspension, but are incapable of imparting to it a sedimentation stability. For this reason, the consumption of different varieties of clay used for preparation of 1 m³ of a stable mud fluid may vary within a fairly wide range. If, for instance, there must be less than 100 kg of a high- quality sodium bentonite per m³, the amount of low colloidal clay will have to exceed 800 kg.

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 a 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.

In fresh water there takes; place a surfieial dissociation of bentonite, viz. the adsorbed cations of Na⁺, Ca⁺⁺, Mg⁺⁺ and other elements break away from the surface of the particles and the latter becomes negatively charged. The majority of these cations are held near the surface of the clay particle by the adsorption forces and the force of the electr c field around the particle at a distance of one- two molecules, forming, as it were, a plane capacitor with two plates (so-called double Helmholtz electric layer), on one of which a negative charge of ths clay particle is concentrated and on the other the positive charge of countcrions. A part of cations, however, move away under the effect of thermal motion over a greater distance from the particle and form a diffusive portion of the double electric layer, or the diffusion layer of Guit. Between the ions of the Helmholtz layer and the diffusion layer a continuous equilibrium exchange goes on. Within the limits of the Helmholtz layer is in evidence a steep drop of the electric potential, whereas in the diffusion layer the potential declines more smoothly.

For the stability of mud fluids of prime importance is the magnitude of the potential at the AB boundary of slippage during movement of the liquid phase respective the solid one, which is commonly known as the zeta-potential.

The surfieial dissociation results in the formation of an ionic cloud around each clay scale. S ince the water molecules appear as dipoles they become oriented in the electric field of the scale and are attracted to it by their positive charges, while to the negative dipole charges are attracted new water molecules which become oriented in a manner similar to the former. At the same time, subject to hydration are cations broken, away from the surface of the scale, with water dipoles getting oriented around them as well.

Thus, a specific cloud of oriented water, molecules, inclusived cations, forms around the clay scale. Such a cloud of

a tented water molecules is called hydration envelope, while the aggregate consisting of the clay particle, double¹ electric layer and the hydration envelope represents the micelle, which is electrically neutral.

The water in hydration envelopes is physically combined. In the inner layers of the envelope this water has a structure and properties of ice, viz. it is resilient, possesses an elevated viscosity and mechanical strength. With increasing distance from the scale surface the bonding forces get weaker, the orientation of water molecules becomes less marked, the strength of the hydration envelope decreases and its properties approach those of ordinary water. The thickness of the hydration envelope depends in a great measure on the magnitude of the clay particle charge and the valency of counterions. The greater the particle's charge and lower the valency of counterions, the more intensively develops the ionic cloud and the stronger becomes hydration of the clay scale.

Between adjacent hydrated clay scales there exist forces of molecular attraction, that diminish parallel with increasing distance between the scales by following the power lav/ and forces of electric repulsion between the double electric layers which also diminish with increasing distance, but by following the exponential law. The geometrical addition of attraction and repulsion energies demonstrates that at great distances between the scales the energy of molecular attraction surpasses somewhat that of electric repulsion. With medium distances of approximately 10~⁵ cm the odds are in favour of the electric repulsion forces, while at short distances of about 10~⁷ the forces of attraction have the upper hand again. Consequently, to have two scales stick together some outside energy must be imparted to them, the one that would be in excess of the repulsion energy at medium distances, e.g. capable of overcoming the energy barrier represented by the positive peak. Should the outside energy imparted to the scales be insufficient to overcome this energy barrier, the approximation of the scales so as to achieve their complete fusion is impossible. The higher the zeta-potential and the energy barrier, the more stable is the clay suspension, l his appears to be the key factor in the stability of clay suspensions.

The thickness of hydration envelopes on the surface of clay scales is dissimilar, being maximal on plane faces and minimal on edges and at the scale apices. With irregular thermal motion, water molecules impinging on the scales impart some energy to them, make them move. When moving, the hydrated scales collide with one another. It is obvious that the rupture of hydration envelopes on colliding is more probable in places where they are the thinnest and, consequently, where less energy is required for their rupture. Hence, the hydration envelopes are the second factor contributing to the stability of clay suspensions.

During mechanical grinding of the clay, the crystal lattice can be destroyed in such a manner as to have concentrated at the apices and on the edges of the scales not only fairly high-power negative but also positive charges. Upon collision of the scales on their apices and edges, the rupture of hydration envelopes and partial adhesion occur, above all, under the effect of attraction forces between opposite charges. At rest, the number of clay scales sticking together with their apices or edges gradually increases. With the passage of time they form a specific honeycomb structure that spreads throughout the whole of clay suspension volume. The structure gradually gains in strength owing to adhesion of ever new clay scales and approaches asymptotically a certain limit. Thanks to such a structure the mud is capable of keeping suspended fairly large particles of the solid phase, including fragments of drilled-out rocks.

On stirring the mud solution, its structure disaggregates and it becomes fluid again. The ability of fluids to thicken at rest as a result of the structure formation and become mobile afresh on its agitation or shaking is known by the term of thixotropy.

The particles can stick together in two ways. Firstly, the particles can agglutinate on colliding with their apices and edges and thus form a honeycomb structure whose cells contain free water and inert particles of the solid phase. Then the hydration envelopes remain intact on the most of the particle surface (and above all on plane faces). This phenomenon is known by the name of hydrophilic coagulation.

Secondly, under the effect of certain factors the particles can lose their charge and become devoid of hydration envelopes. In this case, on colliding even with their plane faces they will agglutinate and form bigger aggregates which under the effect of gravity settle out from the mud which then splits up into two phases. Such a coagulation is known as hydrophobic, or as flocculation.

As the degree of the drilling fluid mineralization increases, the coagulation phenomena get more intensive and the stability of the fluid deteriorates. To maintain the preassigned properties of the mud it is subjected to treatment with chemical reagents. The higher the degree of mineralization, the more difficult it is to keep stable the properties of the mud, the more complicated its treatment, the greater consumption of reagents and, consequently, the more costly is the drilling fluid itself.

Hence, when running the risk of a heavy mineralization of the drilling fluid it is advisable in preparing the latter to use salt-tolerant palygorskite clay as a source of the colloidal fraction. Solutions with palygorskite are prepared with fresh water, for then the clay better breaks up into unit scales, salt being added thereafter.

Text 2

Lignosulphonates Mud Fluids and Their Derivatives

The incrusting material of wood and vegetable masses is lignine. When boiling wood with aqueous solutions of sulphurous acid and its salts for the purpose of obtaining wood pulp (cellulose) there appear by-products containing lignosulphonic acids and their salts, along with sugar, tannides, proteins, resins and other components. Following neutralization of these products, fermentation of the bulk of sugars and their separation for production of alcohol and yeasts there remains so-called sulphite cellulose liquor. It contains a large amount of calcic and other salts of lignosulphonic acids and may conventionally be designated as calcium lignosulphonate. The industry delivers this product to drilling enterprises as a concentrated liquid or paste of dark-brown colour, or as a light-brown powder with pH ranging between 4 and 7.

Lignosulphonate is introduced into fresh water-base muds together with alkali and often also with lime, and into saline solutions, without alkali. Lignosulphonate effectively forces down the funnel viscosity and gel strength of muds, as well as water loss of heavily saline fluids (brine muds). On addition of this agent to fresh water-base muds their filtration loss goes up. The agent is less effective with declining salinity, while in poorly mineralized and fresh water-base solutions its effect diminishes also with decreasing pll. Its optimal addition in primary treatment of salinized drilling fluids comprises from 1 to 5 per cent (calculated in terms of dry substance) and during secondary treatment, less than 1 per cent.

Modified lignosulphonates. The effectiveness of the protective action produced by lignosulphonates and, consequently, their ability to keep down filtration losses can be augmented if the agent's molecules are made bigger. The enlargement of the molecules or their condensation is realized as a result of the lignosulphonates interaction with formalin in the presence of sulphuric acid and at an elevated temperature. To avert corrosion and raise the salt sistance, phenol (phenylic acid) is added to the reaction mixture, along with chromat.es, to increase its thermal stability. Such modifications of lignosulphonates are known by the name of condensed lignosulphonates available in three brands both as liquids and powde rs. The liquid product has a density of roughly 1100 kg/m³ and pH - 8-9.

The condensed lignosulphonate of brand 1 contains small amounts of phenols and serves the purpose of reducing water loss and viscosity of fresh-water base, poorly-mineralized and lime-base muds at temperatures not exceeding 100°C. An optimal amount of the additive during primary treatment should be from I to 3 per cent, cal culated to the value of dry substance.

The condensed lignosidphonate of brand 2 carries a much greater proportion of phenols and is distinguished by a higher salt- resistance or salinity tolerance. It serves to reduce filtration losses and viscosity of fresh-water, poorly and medium-mineralized muds and also of calcium-chloride drilling fluids at temperatures of up to 130°C.

The condensated lignosulphonate of brand 3 contains, apart from phenols, also chromâtes. It is used to keep down the water loss and viscosity of fresh-water and poorly-mineralized muds at temperatures of up to 200°C. At temperatures of up to 150°C its optimal addition is from 1 to 2 per cent and at higher temperatures up to 3-3.5 per cent.

At higher temperatures the protective action of lignosulphonates decreases quite significantly with the rising degree of mineralization.

The condensation of lignosulphonates molecules can also be achieved through their oxidation with chlorine, nitric acid and chromates. Wide application have found such products of condensation as chromolignosulphonates and ferrochromo- lignosulphonates.

Chromolignosulphonate is put out in the USA under the trade name of Oksil. It is intended for reducing the funnel viscosity and rheological properties of fresh-water, mineralized, lime- and gypsum-base drilling fluids and also for keeping down the water loss of nonmineralized mud fluids and magnesium hydrogels. In treating mud fluids its optimal addition is up to 1 per cent (calculated to the value of dry substance). The agent is introduced into the drilling fluid treated with alkali to raise pH. The treatment is most effective with pH ■= 9-10.

The heat resistance of nonmineralized drilling fluids after their treatment with Oksil reaches 200°C and that of brine- and gypsum-base ones up to 160°C.

Ferrochromolignosulphonates differ from

chromolignosulphonates in that some of the chromium atoms therein are substituted by iron. They bring down effectively the funnel viscosity of fresh-water, little- and medium-mineralized muds, and also gypsum and calcium chloride drilling fluids. The thermal stability of mud fluids treated with ferrochromolignosulphonates is as high as 180-200°C.

Lignosulphonates are compatible with nearly all chemical agents. Their common shortcoming is foaming of drilling fluids, especially of nonmineralized ones. Therefore, they should be employed together with froth breakers.

Lignine derivatives. These are obtained by treating lignine hydrolysate, a bulk waste product of hydrolytic industry, with oxidants. They effectively depress the funnel viscosity and gel strength and, quite often, also reduce the filtration loss of mud fluids

with pH = 8-10, but, unlike lignosulphonates, produce no foaming thereof.

Nitrolignine is a light-brown coloured powder, insoluble in water. For treating the drilling fluid it is used in the form of an aqueous-alkaline solution of a 5-10% concentration. Depending upon the composition and pH of the fluid the nitrolignine-to-alkali ratio varies from 1: 0.1 to 1 : 0.5 (calculated to the value of dry substance). It is designed for the treatment of nonmineralized and lime-base mud fluids, the optimal amount of the additive comprising from 0.2 to 0.5 per cent. Nitrolignine can be also used in treating brine mud fluids, stabilized with water-loss reducing agents. It is recommended that pFI of the drilling fluid be kept at about 10.

Sunil - a product of nitrolignine reduction with sulphites, is a darkish-brown liquid with pH of around 8, water-soluble. It is used for the treatment of both fresh-water arid mineralized drilling fluids, its optimal addition comprising from 0.2 to 0.5 per cent (calculated to the value of dry substance). With additions of 1.5-2 per cent, sunil lowers water loss of nonmineralized mud fluids.

Starchy agents. These tend to effectively lower filtration losses and viscosity of medium- and heavily-mineralized drilling fluids, including these containing polyvalent cation salts, the ones that act as strongest coagulants. They can also be employed for keeping down water losses of little mineralized mud fluids, but then their viscosity increases.

Natural starches are poorly soluble in cold water. Therefore, in bating mud fluids use is made of aqueous alkaline solutions of a 5 to 10 per cent concentration with a NaOH-to-starch ratio of 1:10 to 1 : 2.5 (with respect to the dry starch mass). The starchy is prepared directly at the drill rig before proceeding with the treatment of the mud fluids, for lengthy storage adversely affects its quality. Treatment is most effective when pH of the drilling fluid filtrate is higher than 10. In primary treatment of a highly mineralized drilling fluid optimal addition of the agent amounts to 1.5-3 per cent (calculated to the value of dry starch). In cases of repeated treatment the amount of the agent spent varies from 0.5 to 1.5 per cent.

The thermal stability of the stairchy agent does not exceed 120°C. An important shortcoming of the starch is its tendency to rot under the effect of bacteria and enzymes. The decay of starch is attended by liberation of a great quantity of gaseous substances having an offensive odour and by foaming of the drilling-fluid. The fluid in which the process of decay has begun is to be fully replaced, for to improve its properties is practically impossible. To avert fermentative destruction it is recommended that the starch pH be brought up to 11.5-12 and salinity maintained at not less than 20 per cent. It is also advisable to introduce antiseptics (chlorinated lime, formaldehyde, formalin, paraformaldehyde, phenylic acid, catapine, etc.), which suppress the vital activity of bacteria. The use of antiseptics yields the greatest effect.

Modified starches. These are prepared by treating natural starches with antiseptics and sodium carbonate, desiccation at 150- 160°C and subsequent grinding. In production of modified starch potassium chrome alums are used as an antiseptic. The ready-made product is a cream-coloured powder, readily soluble in water. To reduce water loss the modified starch may be introduced into the drilling fluid in its powder form without preliminary dissolution. The modified starch is distinguished by its higher fermentation resistance within a broad range of the mud fluid pH. In primary treatment its optimal addition does not exceed 3 per cent and in the repeated treatment, varies from 0.3 to 0.7 per cent. It is fully compatible with other agents.

The thermal stability of starchy agents can be raised somewhat through addition of Oksil

The effect of starchy agents is greater when they are used in combination with other reagents (with carboxymethyl cellulose or hypan, for example).

Humates. The base of these agents form sodium salts of huffiic acids contained in lignites (brown coal) and peat. These salts come in consequence of interaction of an aqueous solutionol caustic soda with finally ground lignite (or peat). For obtaining humate agents, brown coals containing no less than 35 per cent of humic substances are utilized. The quality of the prepared agent depends upon the proportion of humic substances in M initial raw material, on the alkali-coal ratio, temperature, time and on other factors. The alkali-coal ratio varies in the range of from 10:1 to 4:1. The optimal compounding formulation of the agent for treating mud fluids is found by experimentation.

At the manufacturing plants the powdered humate agent is prepared through irrigation of dried brown coal with concentrated (40 ± 45 per cent). In the USA wide use finds also pasty hamate agent which is obtained through mixing of humidified brown coal with concentrated alkali, subsequent briquetting and air drying. The moisture content of briquettes is about 50 per cent.

The humate agent is used most widely and is one of the cheapest and most accessible compound. It is fully compatible with the majority of reagents employed for the treatment of drilling fluids. Its purpose is to reduce water loss and, often, viscosity of fresh-water and low-salinity mud fluids at temperatures of approximately up to 140°C. At higher temperatures 0.01-0.25 per cent of sodium or potassium chromates or bichromates are added to mud fluids together with the humate agent. Sodium humates become adsorbed on the surface of clayey particles in the mud fluid and prevent mutual cohesion of these particles.

Should a drilling fluid be repeatedly treated with a humate agent it can become structureless, its gel strength then falls down to zero and filter cakes formed by such fluids display a high degree of clamminess. In order to avoid this the treatment with a humate agent should be alternated with that involving some other reagents. Especially effective is combined use of a humate agent with chromolignosulphonates.

With a higher salinity the effect of humate agents falls drastically even at not too high temperatures, this being its major disadvantage.

The nitrohumate agent is obtained through treatment of brown coal with nitric acid and alkali. The agent is supplied in powdery form. It is used for reducing viscosity and water loss of fresh water-base, little- and medium-salified mud fluids.

Polyphenol agents. This group embraces substances of vegetable (quebracho, fir, pine, oak extracts) and synthetic origin,

sulphurization products of natural substances and also condensed phenol.

Quebracho is a finely ground brown-coloured powder obtained from the bark of the South-American tree of the same name. It contains 60 to 70 per cent of tannins, largely pyrocatechol ones. The agent is employed together with alkali in a proportion of 1 : 1 to 1 : 5. It is apt to effectively depress viscosity and gel strength of fresh water-base and little-mineralized and also lime-base muds at temperatures ranging from 120 to 140°C. At higher temperatures the efficiency of the agent drastically decreases, even in cases of low salinity. It is well fit for use with all other agents, being particularly often employed together with humates.

Sulcor is a sulphurization product of alkaline fir-tree bark extracts. The agent has an appearance of a dark mass readily soluble in water. It effectively brings down furmel viscosity, gel strength and cuts down filtration loss of fresh water-base muds and is well suitable for use with all other agents. Its optimal addition amounts to 0.1-0.5 per cent with pH = 8-11.

Lignitic polyphenol is obtained through condensation of phenol contained in by-products of wood processing with formaldehyde in an alkaline medium and subsequent sulphurization. It effectively reduces funnel viscosity, gel strength and fresh­water muds filtration loss at pH = 8-11. Its optimal addition is 0.2- 0.5 per cent. Its effect quickly falls off in muds even of little salinity, especially at elevated temperatures.

The polyphenol agents are capable of foaming the drilling fluid and therefore they are introduced together with froth breakers.

Synthetic agents with acrylic polymers as their base. These are distinguished by their high heat resistance (up to 200-250°C) and complete fermentative stability. In the USA most popular are hypan, metas and polyacrylamide.

Hypan or hydrolyzed polyacrylonitrile is a viscid liquid of a yellow to darkish-brown colour, smelling of ammonium. It is used to cut down water loss of fresh water, salified (with sodium sulphate or chloride) and lime-base mud fluids, funnel viscosity of fresh water muds then going up. The manufacturers supply hypan of two brands: of high and medium viscidity. The former lowers the

water loss much stronger, but produces greater thickening of the drilling fluid treated with it, especially when there is an elevated concentration of the solid phase. With growing mineralization the gel strength of the mud fluid, following its treatment with hypan, can be brought down to zero

Optimal addit ion of hy pari at 120°C varies from 0.5 to 0.75 per cent, and at highe - temperatures may be 2-2.5 times higher.

The major shcrtcoming of hypan is its high sensitivity to salts of calcium and other polyvalent metals and metalloids.

Metas is a powdered compound of white or yellowish-gray colour, difficultly soluble in fresh or brine water, but readily soluble in a slightly alkalized water. As concerns its capacity to keep down filtration loss of fresh-water mud fluids or of the ones carrying sodium chlorides or sulphates at high temperatures, it is equivalent and, possibly, even superior to hypan. Like all agents with acrylic polymers as their base, metas is highly responsive to salts of polyvalent cations.

Polyacrytamice is a highly viscid liquid and a strong coagulant. It is used for the treatment of mud fluids with a low solid- phaseconcentration. The agent effectively reduces water loss and raises the viscidity of such muds.

Inorganic electrolytes. In treating mud fluids wide use have found electrolytes, such as caustic and calcined soda, water-soluble glass phosphates, chlorides, calcium sulphates and lime.