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. При більш високій температурі препарат розкладається і витрати 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, каїтіон 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/m³, 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 ahd 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.

2. Highly calcic muds, where calcium chloride serves the part of an inhibitor, lignosulphonates and chromolignosulphonates act as thinners, while the condensed lignosulphonate or starch figure as a water-loss control agent. The 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).

2. 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 1.0 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.