4. Supply a heading for Text 2.

5. Speak about four types of the drilling fluids.

6. Translate the following sentences into English using the words and expressions from Text 1 and Text 2.

1. При бурінні промивальна рідина повинна забезпечувати ефективне і повне очищення забою від вибурених частинок і винесення їх на поверхню:

2. Промивальна рідина створює на стінки свердловини протитиск, достатній для запобігання притоку пластових рідин і газів.

3. Проте цей тиск не повинен бути надто високим, щоб уникнути різкого зниження ефективності буріння, а також гідравлічного розриву порід або розкриття природних мікротріщин і поглинання промивальної рідини.

4. Промивальна рідина передає енергію від бурових насосів, встановлених на поверхні, вибійному двигуну при турбінному бурінні.

5. Гіри бурінні свердловин найбільш широко застосовують рідини на водній основі, а також газоподібні агенти і аеровані рідини.

Unit 9

Water-Base Drilling Fluids

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

penetrate, viscosity, permeable, rigidity, wetting, humidify, prevent, contribute, cave, dense, differential, average, suspend, stick, sediment, saturate, pipe, inhibitor, delay, oxidative, trap, aqueous, inherent, brine, dilution, lattice, montmorillonite, cell, tetrahedron, dispersion, apt, swell, bulk up. pellet, suspend, treating, alkali, piercing, intersaline, subsaline, starch.

2. Read Text 1:

Text 1 Water

In many areas most readily obtainable and cheap natural liquid is fresh or mineralized water. This is why it was precisely water that was used during the initial period marking the development of rotary drilling.

Water cools the bit and friction surfaces of the drilling shall better than other lieuids. At a sufficiently high flow rate, it can very effectively remove the drilied-out rock cuttings from the bottom hole and from the bore of the well. Water is satisfactorily cleared from fragments of the drilled-out rock even in comparatively simple water- settling systems sir ce it is devoid of thixo-tropic properties. When the coefficients of formation pressure abnoimality Ca < 1. the hydrostatic pressure of the water column in the well proves sufficiently great to avert the influx of formation fluids.

Being the lightest among the liquids under consideration, water exerts lesser pressure on the bottom hole face. It penetrates freely the voids and microfractures in the rock, preventing closure of the latter, and thus facilitates breaking up the face with the bit. Therefore with water flushing the rock, breakdown speed is higher than in flushing with other fluids of the group under review.

Inasmuch as viscosity and density of water are insignificant, flushing with water requires less power than with other fluids of the group. Thanks to low viscosity of water, its flow is always turbulent, which makes for better removal of fragments from the well and decreases the possible development of a loose crust of drilled- outparticles on the permeable sections of :he borehole walls. Furthermore, the use of water helps improve working conditions of the drilling crew, for in this case there is no need to prepare hundreds of cubic metres of drilling fluid.

But water is not a universal drilling fluid. A number of important shortcomings restrict its usage. It is krown that the rigidity of some rocks on their wetting is affected quite noticeably; they acquire the ability of plastic flow under much lower stresses than in the nonhumidificd state. Water is not only incapable of preventing humidification, but actually contributes to it. Low viscosity of waiter facilitates its gaining access into the minutest pores of unstable rocks, which accelerates their deformation and caving.

With water circulation, no dense crust of the solid-phase fine particles forms on the permeable walls of the borehole, the one that is capable of offering high resistance to filtration of the drilling fluid i nto the surrounding rocks. Even with a small pressure differential water is easily filtered through fine pores in the rock. On the other hand, in drilling off of highly porous and especially fissured rocks with the coefficient of abnormality less than unity the water can be absorbed very quickly. Experience teaches us that, on the average, the volume flow rate of water used in drill ing is 6-8 times superior to that of other fluids in the group under considerat ion. This must obviously be taken account of in choosing the type of the drilling fluid, since the greater flow rate may result in an increased cost of the well. An intensive loss of water can also lead to an inadequate cleanout of the well from the drilled-out rock fragments (cuttings).

Water does not possess thixotropic properties and therefore cannot hold suspended solid particles at rest. Once circulation is discontinued the drilled-out fragments partly stick to projections in the borehole walls and partly settle down onto the bottom hole face. The sediment of drilled-out fragments amassed near face can, while getting compacted, block the drilling string, especially when there are clayey particles amidst these fragments. In running in a new bit and lifting a worn one from the bottom hole the well has to be flushed more thoroughly, for otherwise the bit and the bottom drive engine can get silted by the sediment.

Water easily dissolves many chemogenic rocks and becomes saturated with salts. For this reason, its corrosive action on the drill pipes and equipment may figure as a very serious factor indeed. To protect equipment against corrosion - inhibitors (substances capable of delaying or preventing oxidative chemical reactions) have to be added to water. As a rule, water affects adversely the oil trapping properties of producing horizons.

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 tlieir 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:

1. readily available liquid medium as its base at a price as dieap as possible;

2. 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;

3. a minimum amount of finely ground heavy minerals, to ensure a preassigned density of the system;

4. 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 Al203x4Si02xH20. The unit cell of its crystal lattice is of

4Q

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]iс 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 arid 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.