There exist several causes responsible for tight pulls and stickings of drilling and casing strings. They are:
1 High excessive pressure of the mud column with a substantial water loss.
2 Tmergence of furrows (furrowing) in the borehole walls, made up of insecure rocks, especially along the section of a heavily deflected bore. Such furrows are usually cut in the borehole walls with tool joints during round trips.
3 Caving-in and crumbling of rocks.
4 Balling consisting of thick filter cake pieces torn off the borehole walls during movement of the pipe string.
5 Balling that consists of drilling breaks falling out of the ascending stream of the mud fluid due to an abrupt drop of its speed at the sites of a sizable enlargement of the well bore (in caverns, for example), or because of disrupted normal circulation (for instance, as a result of scoured threaded pipe joints).
6 Blevated adhesiveness of some filter cakes.
The principal measures aimed at preventing tight pulls and stickings include: the use of muds with a low (not more than 3-5 cm3 per 30 min) water loss and the minimum possible content of a coarse-dispersion solid phase; low excess pressure in the well; prevention of furrowing, first of ali, by considerably curtailing the number of round trips; a thorough clearing of the drilling fluid on the surface and the use of bottom hole sludge traps to remove largesized drilling breaks from the stream near the hole face; observance
of measures designed to preclude earlier reviewed complications; lowering adhesiveness of filter cakes by émulsification of the drilling fluid through the addition of lubricating additives, or some surfactants.
3 Pick out from Text 1 the sentences containing the verbs in the Passive Voice and translate them.
4 Translate the following sentences into English using the words and expressions from Text 1.
1) Для підйому колони труб зі свердловини необхідно докласти зусилля, що значно перевищує вагу самої колони.
2) Іноді при спробі усунути прихват докладають надмірних зусиль, і колона обривається.
3) Через сильне ущільнення кірки в зоні контакту, проникнення у цю зону фільтрату промивальної рідини утруднено.
4) Жолоби у стінках свердловини звичайно виробляються бурильними замками під час спуско-підйомних операцій.
5) Коли буріння припинено, бурильну колону слід систематично провертати розором і не залишати її на довгий час у спокої.
5 Supply a heading for Text 1.
6 Make a plan to Text 1 and retell it,,
7 Find, read and translate the sentences in Text 1 in which we learn about the causes responsible for tight pulls and stickings of drilling and casing strings.
Unit 23 Deep Well Drilling 1 Learn the meaning of the following words, word-combinations and word groups:
depletion, mantle, yield point, reamer, drill collar, shear stress, coat, melt, thermorésistant, drawworks, hp-horsepower, plunger-type pump, piston, bottom hole engine, jet engine, drill stem, round trip, reel up, directed blasting, reject.
Text 1 Deep Well Drilling
Ever growing depletion of oil and gas pools at small depths and growing demand for oil and gas create an urgent need for deep well drilling.
Deep well drilling has already become a very acute problem in many oil producing countries. Deep drilling covers a wide scope of problems to solve and which are not necessarily those connected with exploration for oil and gas alone, but also with the study of formations of the earth crust and underlying upper mantle and with the discovery of new materials including thermonuclear materials. Wells, deeper than 4500 m, are classified as deep wells. Such wells are drilled now in many countries. In 1938 the deepest well's depth was 4573 m. In 1949 the record was raised up to 62:55 m. Later 8000 m wells are drilled in different parts of the world, production being done at the depth as much as 7000 m. Some geologists claim that they see no reason why oil cannot be found at depths from 12000 to 24000 m. That is why the problem of superdeep drilling has been arisen.
Drilling of wells from 4500 to 8000 m has solved many problems related to ultra deep drilling. Ultra deep drilling once mastered will help to discover oil and gas not only in new oil bearing areas but in old, well equipped and construct ed areas.
In view of drilling deeper than 10000 m there have been created new sorts of steel for drill pipes with yield point more than 95 kg/mm2 and for casing more than 140 kg/mm.
In the process of drilling of deep wells with the use of bits, roller type reamers and rubber stabilizers are fixed along the drill collars in order that deviation of the hole may be prevente d.
Weight applied on bit in this case is around 30 to 40 tons. The length of drill collars in deep rotary drilling reach 300 m; pump pressure at 6000 to 7000 m may vary from 125 to 250 atm.
A circulation cycle of mud is sometimes 9 to 10 hours. It should be noted that in deep well drilling under high temperatures the best results were attained in the case of muds with a low hard particles content: oil base muds, emulsion muds with CIVIC and graphite stable chromelygnosuJphate muds. Muds treated with surface active reagents with low percentage of nitrogen and 6 per cent of oil are also used.
3 Make a written translation of the following:
Deep well drilling has already become a very acute problem in many oil producing countries. Deep drilling covers a wide scope of problems to solve and which are not necessarily those connected with exploration for oil and gas alone, but also with the study of formations of the earth crust and underlying upper mantle and with the discovery of new materials including thermonuclear materials. Wells, deeper than 4500 m, are classified as deep wells. Such wells are drilled now in many countries. In 1938 the deepest well's depth was 4573 m. In 1949 the record was raised up to 6255 m. Later 8000 m wells are drilled in different parts of the world, production being done at the depth as much as 7000 m. Some geologists claim that they see no reason why oil cannot be found at depths from 12000 to 24000 m That is why the problem of superdeep drilling has been arisen.
4 Divide Text 1 into logically complete parts and give each a subtitle.
5 Put questions to each part of Text 1 and retell it in English.
6 Read and translate Text 2:
Text 2 Some Perspectives of Drilling Wells up to 15.000 m
Drilling up to 15000 m is considered feasible provided a number of problems are solved. The main problem is the heat barrier. Scientists presume that at approximately 15000 m the temperature of formations can average from 230 to 470°C. Pressure difference at such depths may vary from 1600 to 1900 atm.
High temperature may harmfuly affect physical and mechanical properties of mud, strength of the walls of a well, work of bit, cementing operations and geophysical experiments in a well.
Nowadays there are muds which remain stable under temperatures up to 260°C. However, according to some publications the use of water base muds in the conditions of higher temperatures will not be expedient. Control of water filtration under these conditions will also be difficult.
In order to reduce hydraulic losses in the annulus it is necessary to have minimum static shear stress. A thermally treated metal coat on a bit will presumedly melt arid under the influence of different loads the roller's teeth will deform which necessitates more effective cooling of the bit. It is natural that specific conditions of superdeep wells will necessitate applipation of special therrnoresistart cementing materials and cementing units for pressures of 1000 atm and higher.
In superdeep drilling drawworks and pumps are most important elements of equipment. There are drawworks with a maximum drum load 45 tons. After partial improvement such drawworks can be incorporated into superdeep drilling.
Mud pumps must have around 1800 hp and ensure continuous circulation of the well at 350 atm. Plunger-type pumps ensuring better sealing of the piston in the cylinder are considered prospective for high depths.
Drilling up to 15000 m and deeper may require reconsideration of many problems in drilling, and probably will require new methods of drilling. Such methods of drilling as explosive drilling, flexodrilling and bottom hole engines are very interesting and prospective for superdeep drilling.
Explosive drilling may prove rather efficient in drilling highly hard formations. The gist of this method lies in destruction of formations by explosive charges, which are endlessly fed to the bottom. The use of atomic and jet engines can be foreseen for superdeep drilling.
Research institutions of many countries work at the problem of drilling without steel pipes with the help of a strong flexible drill- stern. Mud is pumped to the bottom tlirough this stem. The bit may receive rotation from an electrodrill or a turbodrill. The advantage of this method is in saving steel pipes. It also facilitates round trips and reduces their time. When the bit is being pulled out the flex-stem is reeled up.
It should be noted also that in superdeep-drilling aside from first class powerful machinery and advanced technology of drilling there will arise necessity in skilled, high ly qualified specialists in drilling.
7 Speak about the perspectives of deep well drilling.
8 Speak about the problems tha t deep drilling is used to solve.
9 Write a summary of Text 2.
CONTROL TASKS
1 Answer the questions:
1 What can cause the blowout?
2 What measures can be taken to avoid lost circulation?
3 Where and when do circulation losses occur?
4 What are the results of excessive caving?
5 What problems is deep drilling used to solve?
6 What are the most common causes of frozen drill pipe?
7 What does the inflow intensity depend on?
8 What should be done to prevent the inlfux of formation fluids and gases into the well?
9 What causes crumbling, caving-in of the rock and narrowing of the well bores?
10 What are the causes responsible for tight pulls and stickings of drilling and casing strings?
2 Give English equivalents of the following:
втрата циркуляції | звуження стовбура свердловини |
обважнена бурильна труба | клапан робочої труби |
техніка вичікування | буріння без виносу породи на поверхню |
стовп промивальної рідини | розширення стовбура свердловини |
місце прихоплення інструменту | плунжерна помпа |
операція опусканя-піднімання | утворення сальників |
тампонуючий матеріал | швидкість буріня |
вартість свердловини | ущільнювач |
поглиблення свердловини | зворотний клапан |
проміжне промивання | труба-стояк |
зворотний потік води | шламоуловлювач |
дотримання заходів | тривалість освоєння свердловини |
висхідна швидкість | тонкодисперсний |
підвищена водонасиченість | гідророзрив |
3 Match the terms with their definitions:
|
4 Tell whether each of the following statements is true or false according to the text. Correct the false statements to make them true:
1 Circulation losses occur when the rock has open fractures, and the pressure exerted by the mud on the borehole walls does not exceed the formation pressure in the given horizon.
2 Circulation losses of great intensity are commonly referred to as complete, or catastrophic.
3 When adding mud into the well at the time of the pipe string hoisting it is not recommended to make use of automatic units.
4 One of the causes responsible for caving-in of rocks is a changed stress state in the rock traversed by drilling.
5 In the case of intensive gas-oil showings, instances of demolished wellhead and drilling equipment, of explosions and fires are of infrequent occurrence.
5 Make a written translation of the following:
To hoist a pipe string out of the well, it becomes necessary on many occasions to apply a force that is appreciably (10-20 per cent and more) in excess of the: weight of the string itself. Such phenomena are known by the name of tight pulls or tightenings. Sometimes, to start off the string and bring it up to the ground surface an effort closely approaching the ultimate one that the strength of the pipe's permits and even surpassing it has to be applied. Such tight pulls are called stickings. A sticking is a trouble arising out o ' non-observ ance of the drilling technology or of an improper consideration of features specific for the geological structure of the deposit, lithological composition and properties of the rocks, while elaborating the technology of drilling. At times, in an attempt at eliminating sticking, exorbitant forces are applied and the string breaks asunder. In this case the sticking is aggravated by a breakdown. For this reason, stickings are often classified as breakdowns.
PART 6 DRILLING IN AND TESTING OF PAY BEDS
Unit 24
Influence of Drilling Fluid on the Collecting Properties
of Pay Beds
1 Learn the meaning of the following words, word-combinations and word groups:
futile, inferior, bulk, influx, contingent, pay area, well completion time, suspend, augment, differential, uphole velocity, permeability, fine-dispersed, cross-section, pervious, clog, fissure, scores, collecting properties of the sands, slurry, reservoir, connate, swell, saturation, elevated water abundance, emergence, biphasic, diminish, precipitation, foul.
2 Read and translate Text 1:
Text 1
The final aim of drilling oil and gas wells is to obtain the desired products (crude oil and gas). Great expenditures of labour, materials and money may prove futile if it becomes impossible to achieve the inflow of crude oil and gas; they will also appear in a large measure unjustifiable in the event of the crude oil and gas inflow being much inferior to the potentially possible one. The final result of drilling, e.g. the bulk of the influx and the well completion time, are contingent upon the quality of the drilling fluid used in drilling over a pay area, the method employed in approaching it and the way of completing the well.
Observations made in oil-fields over lengthy periods of time along with special long-term investigations have proven that the mud fluid is capable of exercising great influence on the well completion time, the labour-consuming nature of this operation and the size of the crude oil and gas influx (production rate). One may cite many examples when it proved impossible to obtain crude inflow from a well sunk with the application for its flushing of a chemically untreated clay mud, although the neighbouring wells put clown with other drilling fluids used for flushing showed fairly large yields.
There are known many instances when wells sunk at a high schedule speed with fresh v/ater flushing were completed with considerable difficulty and their production rate was much lower than that of wells drilled with the use of a high-standard clay mud. Much time was spent in completing them, while the economy achieved thanks to a high drilling speed was lost completely or partially on account of exuberantly prolonged work of completion.
Not infrequent are cases when an intensive gassing of the mud or the appearance in it of oil are observed in the course of drilli ng. On the other hand, following cementation of the well and perforation of the casing it becomes impossible to obtain any inflow of gas (or crude oil) from the reservoir.
Quite often an abundant influx of crude oil or gas occurs in testing of the well. But if the operation of such a well has to be temporarily suspended, and for this purpose it is filled with a clay mud, on its recompletion the recovery becomes, as a rule, substantially lower and the inflow induction work greatly increases in length. Sometimes il becomes impossible to complete at all such a well.
What is then the reason for such a potent action produced by the quality of the mud fluid on an effective opening of a pay bed?
While pay sands (beds) are being drilled over, a liquid phase is filtering out into it from the mud fluid. The volume of the filtrate entering the reservoir augments with increasing water loss of the mud, the time spent in drilling over the bed, the pressure differential, the uphole velocity in the annulus, the temperature of the mud, and with decreasing clearance between the drilling string and the borehole walls. The radius of the filtrate penetration into the pay bed may be as great as a few metres. The pay beds practically carry a certain amount of clayey and other particles, sensitive to the acti on of the filtrate and capable of interacting with it.
Another factor impairing permeability of collecting sands under the effect of the mud fluid is penetration of fine-dispersed solid phase particles (elay particles and those of weighting material) into the sands along large pores and microfractures, closu re of these pores or reduction of their effective cross-section.
The higher the permeability of the rock, the more, as a rule, the number of large pore channels therein. Therefore, a highly perv ious rock is apt to be clogged to a greater extent with the solid phase particles than a little pervious one and the degree of its impaired permeability is greater. In a number of cases the permeability of sandstones, for instance, decreases for this reason as much as 10 and more times. The solid phase particles, apparently, do not enter at all into granulated collecting sands with a very low permeability.
It is not infrequent that in the co urse of dr illing the high pressure exerted by the column of mud fluid causes hyd raulic fracturing of the pay bed, or opening of natural, fractures therein. In this case the w hole of the mud fluid spreads about along the fissures and goes scores of metres deep down into the bed. Then, the collecting properties of the sands are liable to suffer much more badly. Of no less grave consequences is hydraulic fracturing occurring at the time of cementation and subsequent penetration along the fractures of the cement slurry and of its filtrate iinto the reservoir.
Since a pay bed always carries a certain amount of connate water, the penetration of an aqueous filtrate into the reservoir gives rise to swelling of the clay particles and to a subsequent increase of water saturation. During completion of a we.il, oil and gas have to move toward the well via a zone around its be re characterized by an elevated water abundance. This results in the emergence of a biphasic flow (crude oil and water, or gas and water) and the effective permeability for the oil (gas) diminishes. The bulking up of argillaceous rocks, formation of insoluble salts and their precipitations, as well as that of resins, paraffins and other solid particles, into a sediment, consolidation of this sediment and clogging of the pore channels, all this, naturally, does not occur instantaneously. Therefore, the degree of damage due to the fouling of the reservoir with the mud fluid arid its filtrate is largely dependent upon the duration of their action: the longer it is, the greater the damage.
3 Give English equivalents of the following:
продуктивний об’єкт, тривалість освоєння свердловини, перепад тиску, забруднюватись, властивості колекторів пласту, підвищена водонасиченість, випадання в осад, забивати пори.
4 Translate the following sentences into English using the words and expressions from Text 1.
1) Відомо багато випадків, коли свердловини, пробурені з дуже високою швидкістю при промиванні прісною водою, були менш продуктивні, ніж свердловини, пробурені із застоуванням високоякісного глинистого розчину.
2) Часто при випробуванні свердловини одержують інтенсивний притік нафти або газу.
3) Іноді свердловину взагалі не вдається освоїти.
4) Під час розбурювання продуктивного пласту у нього з промивальної рідини фільтрується рідка фаза.
5) Найбільша кількість твердих частинок осідає в порах поблизу стінок свердловини, і саме тут трапляється найбільше погіршення проникності.
5 Pick out from Text 1 all the sentences with adjectives used in different degrees of comparison and translate them.
6 Supply a heading for Text 1.
7 Divide Text 1 into logically complete parts and give each a subtitle.
8 Put questions to each part of Text 1 and retell it in English.
9 Write a summary of Text 1.
Unit 25
The Choice of Mud Fluid for Drilling in the Pay Bed
1 Learn the meaning of the following words, word-combinations and word groups:
quantify, array, contaminate, resort to, hydraulic fracturing, deteriorate, adjust, advance, recovery, drastically, induce, influx, utilization, opening-up, reservoir-bed.
2 Read and translate Text 1:
Text 1
The influence exercised by the mud fluid on the pay bed rock is of an individual nature and depends on man> factors. It is rather difficult to quantify the degree of contamination of a definite pay area by the drilling fluid. But in choosing the mud fluid for drilling over a pay bed two points may be adopted as a guideline.
First, all the drilling muds may be arrayed by the increasing degree of their contaminating action on the reservoir, viz. gaseous agents < oil-base muds < brine-base muds < fresh water-base muds. Weighted muds tend to foul the bed to a greater extent than do nonweighted ones of the same class.
Second, the contaminating action of a mud fluid is the less, the closer its composition and properties of the filtrate approach those of the formation fluid.
The pollution of the productive sand around the well bore zone affects, first and foremost, the time and the amount of’labour spent in completing the well and during its initial operation. With a heavy pollution one has to raise the pressure differential, spend more time in pumping out the fluid from the well and remove the filtrate (and sometimes also the mud itself) from the £irea around the well bore, resort to additional methods of the stimulating action (acid treatment, vibratory action, hydraulic fracturing, etc.).
Not infrequently, because of greatly deteriorated collecting properties of the sands caused by the mud, gross errors are committed in prospecting wells during interpretation of geophysical findings, some of Ihe producing horizons being classified as nonproductive and, therefore, not subjected to testing.
The composition and properties of the mud fluid have a great bearing on the penetration rate (advance). Quite natural are efforts to adjust the composition and properties of the drilling fluid in such a way as to achieve the maximum rate of advance. For example, the application of a water-base mud with a low proportion of clay instead of an oil-base one, or of water in place of a clay mud frequently helps to substantially increase the rate of advance, but this, at the same time, intensifies the contaminating effect on the pay bed. Therefore, in selecting a mud fluid for drilling over a pay bed one should always compare the economy that might be obtained through increasing the speed of the well sinking against losses that are possible as a result of the pay bed pollution and reduction of the production rate, as well as against additional expenses for completing the well.
It is obvious that one has to choose a mud fluid with whose use the savings achieved through a higher drilling rate are greater than the total additional costs of completing the well and its stimulating, as well as the losses due to a reduced recovery during the first period of exploitation. Such a comparison may be made only on the ground of experience in the application of diverse muds in a given district and also in other areas with similar geological and physical conditions specific for the producing zones.
A significant influence on the collecting properties of the productive sands within the zone around the well bore can exercise surfactants applied in the treatment of the mud.
The application of muds treated with properly selected surfactants for drilling in productive strata enables it to minimize their pollution, drastically cut down the time needed for completing the well, reduce pressure differential required for inducing the influx and raise the initial output of the well.
To drill in producing horizons with an abnormality factor, the best oil-base muds are the ones which produce practically no polluting effect on the pay bed. Experience shows that by using such muds the completion of the well and induction of the oil (gas) inflow present no difficulty, while the time spent in completing the well is many times shorter than with utilization of water-base mud fluids. The initial production yielded by wells where drilling in the
pay bed was done by using such muds is by far greater (often by as much as 2-5 times) than is the output of neighbouring wells sunk with water-base muds flushing.
3 Give English equivalents of the following:
порода продуктивного пласта, забруднююча дія промивальної рідини, вдаватись до додаткових способів стимулюючої дії, обробка кислотою, вібровплив, гідророзрив, допускати грубі помилки, інтерпретація геофізичних даних, швидкість буріння свердловини, витрати часу на освоєння свердловини.
4 Translate the following sentences into English using the words and expressions from Text 1.
1) Вплив промивальної рідини на породу продуктивного пласта є індивідуальний і залежить від багатьох чинників.
2) У розвідувальних свердловинах допускаються грубі помилки при інтерпретації геофізичних даних, деякі продуктивні горизонти класифікуються як непродуктивні, і тому їх не опробовують.
3) Ступінь збитків від забруднення пласта промивальною рідиною і її фільтратом істотно залежить від тривалості їх дії: чим довша дія, тим більші збитки.
4) Зменшувати забруднення продуктивного пласта можна, правильно підбираючи мінералогічний і гранулометричний склад твердої фази промивальної рідини.
5) Великий вплив на властивості колекторів при- стовбурової зони продуктивного пласта мають поверхнево- активні речовини, використані для обробки промивальної рідини.
5 Pick out from Text 1 all the sentences with modal verbs and translate them.
6 Supply a heading for Text 1.
7 Make a plan to Text 1 and retell it.
8 Write a summary of Text 1.
Unit 26
Choosing a Metltiod for Opening-up a Reservoir-Bed and an Arrangement of the Ar ea in and around the Hole Face in Producing Wells
1 Learn the meaning of the following words, word-combinations and word groups:
area in, area around, producing well, case off, formation pressure, streak, homogeneous, saturate, permeability, casing shoe, suspend, packer., gas holder, production casing, overlap, slit, mill, back of the bed, competent rock, pierce, gas cap, tap, inrush, accelerated expenditure, feed, formation energy, advance, collar, deflect, side hole, fit out.
2 Read and translate Text 1:
Text 1
By the openir g-up of a reservoir is understood a complex set of operations associated with drilling in, securing the strength and stability of the area in and giround the bottom hole of the well and also with establishing communication between the production string and the reservoir after the well bore has been cased off. The choice of the opening-up method is largely dependent upon the structure of the bed (reservoir), its properties as an oil collector, the composition of fir ids and gases contained in it, the number of productive oil streaks, and on the abnormality factor of formation pressures.
If the pay bed is homogeneous, made up of a strong, competent rock, saturated with a single fluid, and the permeability across the thickness of the bed varies but little, then the well bore opposite such a bed need not be reinforced with a casing. In open holes the casing shoe is placed in the roof (top) of the oil reservoir. With such a casing program of the well the type and properties of the drilling fluid may be chosen by taking account of features specific only for the oil reservoir. In this case it is possible to completely avoid any pollution of the reservoir.
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