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

rock, cohesion, substance, ore, layer, density, voli me, solid, magmatic, sedimentary, porosity, void, to drill, well, clay, said, pore, to diminish, deposit, to saturate, fluid, tensile, resistance, friability, tension, firmness, grain, to augment, contingent, to obey, lateral, pressure, curve, to apply, lag, lattice, creep, bedding, to regain.

2. Read and translate Text 1:

Text 1

The rock is made up of minerals of a mo*e or less invariable composition bound together by forces of molecular interaction (cohesion) that arise either at the; sites of direci: contact of minerals with one another, or at the sites of their contact with mineral particles of extraneous cementing substances. It is only oies and the upper soil layer that do not come under the term of rocks.

varies from 2100 up to 2900 kg/m¹ (for the most common rocks it lies , in the range of2400 to 2700 kg/m³).

4. Find in Text 2 English equivalents for the following words and expressions; make up sentences with these words:

щільність, твердий, вміст, змінювати, містити, магматичні породи, осадові породи, феромагнітний, силікат, зменшувати, збільшувати, кварц.

4. Make a written translation of Text 2.

5. Read Text 3:

Text 3

Quantitatively, porosity is commonly characterized by a coefficient representing a ratio between the volume of voids and the apparent volume of the rock (void ratio). Table 1.1 lists magnitudes of void ratio for rocks most frequently encountered in drilling of oil and gas wells.

fable 1.	Porosity of Sedimentary Rock
Kind of rock	Void ratio, %	Kind of rock	Void ratio, %
Clay	0-0.62	Sandstone	0-0.53
Argillite	0-0.25	Limestone	0-0.45
Aleurolite	0-0.47	Dolomite	0-0.2.7
Sand	2-0.55	Marl	0-0.60

The mass of a unit volume of dry rock in its natural state (with pores and fissures) is known as volume mass. The latter is tantamount to density only in the case of voidless rocks. The volume mass of porous rocks is always inferior to their density, the difference being the more significant, the greater their porosity. As the depth of the rock occurrence increases its porosity diminishes because of compression from superjacent rocks. Therefore, the volume mass of porous rocks of a similar mineralogical composition increases with depth.

The volume mass of most rocks varies from 1500 to 3500 kg/m³, while the volume mass of sedimentary rocks making up petroleum and natural gas deposits usually lies between 1800 and 2500 kg/m³.

The pores of many rocks entering the structure of oil and gas deposits are filled with fluids (fresh or mineralized water, oil, gas).

The volume mass of rocks saturated with dropping fluids is, naturally, superior to that of dry rocks; the difference between them rising parallel with the increase in the porosity and mineralization of water. The volume mass of saturated sedimentary rocks habitually lies in the range from 2000 to 2700 kg/m³, although in individual instances there may be also significant departures from these figures. The magnitude of the rock pressure is a function of the volume mass.

The magnitude of stresses under which a rock disintegrates characterizes its strength. It is to compression that a rock offers the greatest resistance, whereas its tensile strength usually does not exceed 10 per cent of the compressive strength (Table 1.2). This is explained by the friability (brittleness) of the rocks, by numerous local defects and structural non-uniformities, and also by low forces of cohesion between individual particles.

Table 1.2 Relative Strength of Rocks

Designation	Relative strength, %
of rocks	Compression	Shear	Bending	Tension
Sandstones	100	10-20	2-14	2-5
Clav shales	100		f 15-60	r 10-18
Gvosum	100		35	11
Ouartzites	100	5-7		4-5
Basalts	100	55-100
Granites	100 1	9-12	8
Limestones	100	15-20	8-10	10-13
Marble	100	16-40	-	8-10

The strength of a rock is largely dependent upon its mineralogical composition. The strongest rock-forming mineral is quartz, its strength surpassing 500 MPa, while the strength of ferromagnesian silicates and of alumosilicates amounts to 200-500 MPa and that of calcite to 10-20 MPa. Therefore, the strength of a rock commonly accrues with growing content of quartz. The strength is highest in rocks whose density roughly equals that of quartz (about 2700 kg/m³). The strength of a mono-mineral rock is usually superior to that of the polymineral, for the latter nearly always contains weak minerals.

The strength of minerals depends on the size of crystals and diminishes with the increase in their dimensions. This relationship is

particularly significant in crystals measuring less than 0.5 mm.

In rocks the effect of the scale factor on the strength is less marked. This is due 10 the fact that the strength of a rock depends not only on the strength of the minerals, but also on the firmness of bonding at the intercrystalline boundaries separating the mineral grains. The compressive strength of fine-grained arcose sandstone, for example, is nearly twice as great as that of the coarse-grained one; the compressive strength of marble with a grain size of 1 mm is 100 MPa, whereas the strength of fine-grained limestone with grains measuring 3-4 (am amounts to 200-250 MPa. The strength of this limestone is roughly equal to that of coarse-grained granite, although the strength of quartz and of feldspar, constituents of granite, is 10-12 times as high as that of calcite forming limestone and marble.

Among sedimentary rocks, the strength is the greatest in rocks with siliceous cement. In the case of argillaceous cement, the strength of rocks declines drastically.

The strength of rocks of the same name accrues with decreasing porosity, for then the number of contacts between mineral particles augments and the forces of their interaction gain in strength. For instance, with an increase of the volume mass from 1500 up to 2700 kg/m³, caused by reduced porosity, the compressive strength of limestones rises from 5 up to 180 MPa.

The strength of rock:? is affected by the depth of their occurrence and the degree of rnetairiorphization. Thus, the strength of clays occurring at the ground surface is 2-10 MPa, whereas the strength of argillaceous rocks that passed through an initial stage of metamorphization under the effects of high temperature and great pressure exerted by overlying rocks may be as high as 50-100 MPa.

The strength of anisotropic rocks is contingent upon the direction of the active force. The strength in compression of rocks normal to bedding (lamination) or schistosity is, as a rule, greater than is the strength along the bedding. The ratio between strength in compression parallel to bedding and that normal to it is termed the coefficient of anisotropy (or the anisotropy factor). For the majority of rocks the magnitude of this factor varies from 0.3 to 0.8 and only in isotropic rocks alone it equals unity.

The strength of rocks is also influenced by temperature. When it goes up the strength of argillaceous rocks increases due to sintering or metamorphization. With the temperature rising up to 600-800°C, stabilization takes place in compact fine-grained rocks, this being due to the reduction of natural rnicrojointing and an enhanced area of contacts among mineral grains. On the other hand, the strength of chemogenic rocks diminishes with rising temperature, while their plastic properties gain in intensity.

7. Find in Text 3 English equivalents for the following words and expressions; make up sentences with these words:

показник пористості, аргіліт, алевроліт, пісок, пісковик, вапняк, доломіт, мергель, тріщина, стиснення, розтяг, крихкість, ламкість, сланець, мармур, дрібнозернистий, грубозернистий, польовий шпат, глинистий, напружуватись, нашарування, шаруватість, хемогенні породи.

7. Divide Text 3 into logically complete parts and give each a subtitle.

8. Put questions to each part of Text 3 and retell it in English.

9. Pick out from Text 3 all the verbs in the Pa ssivc Voice.

10. Read Text 4:

Text 4 Elasticity

Most of the rock-forming, minerals are elastico-brittle bodies, e.g. they obey Hooke's law and disintegrate when stresses reach the elastic limit.

On the other hand, by the nature of the relationship between deformation and stresses under a static; load, rocks may be classified into three groups: (1) elastico-brittle., subject to Hooke's law; (2) plastic-brittle, whose destruction is preceded by plastic deformation or flow; and (3) highly plastic and heavily porous ones, whose elastic deformation is insignificant.

The elastic properties of rocks are characterized by the modulus of elasticity E and Poisson's ratio p.. By the modulus of elasticity is understood the proportionality constant or factor between nonnal stress in the rock and relative deformation that corresponds to it. Poisson's ratio is the proportionality constant between the unit longitudinal and lateral deformations.

In the majority of rocks the modulus of elasticity E varies from 0.03 X 104 to 1.7 X 105 MPa. Its magnitude is largely dependent upon the mineralogical composition (Table 1.3) and the porosity of the rock, and also on the type of deformation and the magnitude of the applied load. For this reason it is but approximately that one may refer rocks to the category of elastic bodies.

Hence, with growing porosity the modulus of elasticity of rocks diminishes. In tension the modulus of elasticity declines as the load increases; in compression and rising pressure it goes up. This, apparently, is to be attributed to the fact that in tension (and with increasing porosity) the number of contacts between rock grains decreases and the forces of their mutual interaction get weaker, whereas in compression the formerly lost contacts are reestablished and because of their closeness the interaction of mineral particles gains in strength.

Tab	e 1.3 Modulus of Elasticity for Some Rocks
Designation	Modulus	Designation	Modulus
of rocks	of elasticity	of rocks	of elasticity
	EX 10-4,		EX 10-4,
	MPa		MPa
Clavs	0.03	Dolomites	2.1-16.5
Clay shales	1.5-3.0	Quartzites	4.0-10.0
Sandstones	0.5-7.8	Aleurolites	1.7-2.7
Limestones	1.3-8.5	Marble	3.9-9.2

A number of other features specific for rocks are also related to the abovefactor. In rocks, for example, manifestations of elastic hysteresis are observed. In compression the stress-strain curves fail to coincide in applying and relieving the stress. In the case of porous rocks (sandstone, for instance), the relief curve fails to come to the origin of the coordinates, since there is observed a certain residual deformation owing to the creep of the rock. If a rock is exposed to a certain quickly applied pressure, this pressure being subsequently maintained at the same level, the deformation (strain) will then continue increasing for some time. If the pressure is then quickly relieved the rock will show a certain residual strain that disappears completely only after a definite time interval. This phenomenon is designated as elastic lag or aftereffect.

For the majority of sedimentary rocks the values of modulus of elasticity stand below those for corresponding rock-forming minerals. It is in quartzites only that the moduli of elasticity for the rock and quartz are roughly coincident. This is explained by the fact that quartzite is composed of quartz grains bonded together by means of a regenerated quartz cement.

The modulus of elasticity for rocks is also influenced by the texture of the latter. In rocks presenting a clearly pronounced lamination or schistosity the modulus of elasticity in the direction of lamination is ordinarily higher than in the direction normal to lamination, but sometime the reverse is also true.

For most rocks and minerals Poisson's ratio lies within the range of 0,2 - 0.4 and only in quartz it stands abnormally low, roughly at 0.07, which is conditioned by the structural peculiarity of its crystal lattice. With growing porosity Poisson's ratio in some rocks increases and in others - diminishes.