Well Completion and Treatment

If, after borehole measurements and tests, a well is considered worth producing from, it is completed, i.e., equipped with all technical installations necessary for production. Components necessary for the completion are the wellhead, casing, cementing, tubing string or strings (single or multiple completion), and the “bottom hole completion”. This includes the special equipment used in the reservoir zone, i.e., liners, liner hangers, sand filters, packers, and all the ‘‘wireline equipment’’ which can be operated by cable and wire.

A common problem in producing wells is formation damage, i.e. reduction in the natural capability of a reservoir to produce its fluids, such as a decrease in porosity or permeability, or both. Damage can occur near the wellbore face (easier to repair) or deep into the rock (harder to repair). The treatment of the well and of the reservoir formation is intended to increase the productivity of wells or, in other words, to restore an inflow to the well free from restrictions.

Well Treatment

The type of obstruction of the well must be known in order to choose the most suitable treatment from the various possibilities. The obstruction can be caused:

1) by solids from the mud (filter cake);

2) by increased water saturation around the well (water block);

3) by swelling of the clay minerals present in the rock’s matrix;

4) by chemical precipitation;

5) by emulsification.

In practice the first two causes occur most frequently. The obstructions are usually removed by chemical treatments. The most important chemical treatment agents are: aqueous solutions of hydrochloric acid, hydrofluoric acid, acetic acid, citric acid, and surfactants (in concentrations of 0.1 – 5 wt %). Surfactants are added in almost all well treatments in order to promote the dispersion of the solids, to improve the wettability of the rock, and to prevent emulsification.

If it is intended to treat only the borehole wall, it is sufficient to circulate the treatment liquid into the well zone in question. If the obstruction extends into the reservoir bed, e.g., by clay swelling, the treatment liquid must be uniformly injected into the reservoir, avoiding pressure which leads to cracking. In any case, the reaction products should be removed from the reservoir bed or from the well as quickly as possible.

Reservoir Bed Treatments

Two methods basically exist for extensive improvement of the inflow conditions in a reservoir bed of low original permeability:

1) pressure acidizing (usually in carbonate rocks);

2) hydraulic fracturing (frac treatment).

The best-known method of reservoir-bed treatments is fracturing technology, which is mainly used for producing artificial flow paths in the reservoir rock.

Fracturing

Hydraulic fracturing is the process of pumping a fluid into a wellbore at an injection rate that is too great for the formation to accept in a radial flow pattern. As the resistance to flow in the formation increases, the pressure in the wellbore increases to a value that exceeds the breakdown pressure of the formation open to the wellbore. Once the formation “breaks down,” a fracture is formed, and the injected fluid begins moving down the fracture. In most formations, a single, vertical fracture is created that propagates in two directions from the wellbore.

There are many applications for hydraulic fracturing. Hydraulic fracturing can increase the flow rate of oil and/or gas from low-permeability reservoirs, increase the flow rate of oil and/or gas from wells that have been damaged, connect the natural fractures and/or cleats in a formation to the wellbore, decrease the pressure drop around the well to minimize sand production, enhance gravel-packing sand placement, decrease the pressure drop around the well to minimize problems with paraffin deposition, increase the area of drainage or the amount of formation in contact with the wellbore, and connect the full vertical extent of a reservoir to a slanted or horizontal well.

In fracturing, only a part of the injected liquid is available to widen the fracture and act as a medium for transporting the proppant, or for the chemical reaction along the fracture faces. With a widening fracture, the other part of the liquid increasingly migrates into the pore space of the rock. In order to limit this effect, which is unfavorable for the success of the operation, fluid loss agents are added that raise the viscosity and form a filter cake. These agents cause the initially high fluid loss to decrease substantially after the filter cake has built up. Later, these additives become ineffective due to the influence of temperature and pressure, and the production stream reaches the well unhindered.

Pressure acidizing is also a hydraulic fracturing method by injection of acid. In pressure acidizing, however, an increased permeability is achieved by dissolution of a part of the carbonate matrix along the fracture faces.

In order to ensure the success of reservoir bed treatments, a sufficient depth of penetration into the reservoir rock must be achieved. This penetration depth must be greater with less permeable reservoir rock. Penetration depths of 40-70m are usual with vertical or horizontal fractures.

Workover

An important chapter of constant concern for the production engineer is workover technology. More than one million production wells worldwide, of which three quarters are oil wells, require continual upkeep and maintenance and – repeatedly during the course of their use – repair. Thus the number of workover hoists is three to four times the number of drilling rigs. Workovers are often necessary in older wells, which may need smaller diameter tubing, scale or paraffin removal, acid matrix jobs, or completing new zones of interest in a shallower reservoir. Such remedial work can be performed using workover rigs – also known as pulling units or completion rigs – to pull and replace tubing, or by the use of well intervention techniques utilizing coiled tubing.

Workover should always follow a sequence of diagnosis, therapy (work program), operational execution, and monitoring of success. Reliable measurement techniques and supervision of operation and production are the prerequisites for correct diagnosis.

Ex. 4. Decide, whether the following statements are True or False, according to the text.

1. Bottomhole completion includes casing and cementing.

2. Formation damage is usually characterized by decreased permeability or porosity.

3. Well treatment is aimed at restoring the initial productivity of the well.

4. Increased water saturation around the wellbore is a common problem in well production.

5. Acids help to remove water and clay blocks around the wellbore.

6. Well treatment is always extended to the reservoir formation around the well.

7. Pressure acidizing is most effective in sandstone formations.

8. Hydraulic fracturing pressure must be greater than the formation pressure.

9. Most fractures are vertical.

10. Hydraulic fracturing increases the flow rate from damaged wells.

11. In hydraulic fracturing operations, it is necessary to provide the effective migration of fracturing fluid into the formation.

12. Pressure acidizing destroys cement bonds around the wellbore.

13. The more permeable the rock, the greater the penetration of reservoir bed treatments.

14. Workover can be synonym for well repair.

15. Coiled tubing can be useful for scale or paraffin removal.

Ex. 5. Choose the correct answer.

1. Completion components include wellhead, casing, tubing and bottomhole / wellbore completion.

2. Formation damage is the decrease in density / porosity or permeability.

3. Flow obstruction in the well can be caused by swelling of the drilling mud / minerals in the rock.

4. Flow obstructions are usually removed by chemical / mechanical treatments.

5. Surfactants are added in almost all well treatments in order to promote the dispersion / compression of the solids.

6. During well treatment, the products of clay swelling / chemical reaction should be removed from the reservoir bed or from the well as quickly as possible.

7. Pressure acidizing is commonly used to increase permeability / porosity of rock.

8. Hydraulic fracturing is the process of pumping a fluid into a wellbore at an injection rate that is too great for the formation to accept in the axial / radial flow pattern.

9. Hydraulic fracturing can decrease the pressure drop around the well to minimize emulsion formation / sand production.

10. Hydraulic fracturing can increase the area of water saturation / drainage or the amount of formation in contact with the wellbore.

11. During hydraulic fracturing fluid loss agents are added that increase / decrease the viscosity.

12. In hydraulic fracturing / pressure acidizing an increased permeability is achieved by dissolution of a part of the carbonate matrix along the fracture faces.

13. Workovers are often necessary in older wells, which may need smaller diameter tubing or emulsion / paraffin removal.

14. Workover can be performed by the use of well intervention techniques utilizing drill stem / coiled tubing.

Ex. 6. VOCABULARY. In the text above, find the equivalents to the following words and phrases. (The sequence corresponds to their occurrence in the text.)

1. стоит что-л. делать

2. заканчивать (скважину)

3. колонна труб

4. заканчивание забоя скважины

5. хвостовик

6. подвеска хвостовика

7. противопесочный фильтр

8. пакер

9. повреждения призабойной зоны

10. поверхность призабойной зоны

11. восстановить

12. приток

13. ограничение, сужение

14. обработка приствольной зоны

15. препятствие

16. твердые частицы

17. глинистая корка

18. водяной барьер

19. разбухание

20. матрикс (горной породы)

21. химическое осаждение

22. образование эмульсии

23. водный раствор

24. соляная кислота

25. фтороводородная кислота

26. уксусная кислота

27. лимонная кислота

28. поверхностно-активное вещество

29. массовая доля

30. дисперсия

31. набухание глин

32. растрескивание

33. продукты химической реакции

34. кислотная обработка под давлением

35. гидроразрыв пласта

36. искусственный

37. скорость закачки

38. радиальный поток

39. превышать

40. расширяться, распространяться

41. трещиноватость

42. вынос песка

43. гравийный фильтр

44. образование отложений парафина

45. наклонно-направленная скважина

46. расширить

47. проппант, расклинивающий агент

48. антипоглощающая добавка

49. беспрепятственно

50. растворение

51. капитальный ремонт скважин, КРС

52. поддержание в рабочем состоянии

53. техническое обслуживание

54. ремонт

55. подъемное устройство

56. удаление зарастания

57. текущий ремонт

58. агрегат для КРС

59. передвижная установка для заканчивания скважин

60. внутрискважинная обработка

61. гибкие НКТ малого диаметра, койлтюбинг

62. диагностика

63. предпосылка, обязательное условие

Ex. 7. Match words from Column A to the words from Column B in order to form phrases. Translate the resulting phrases into Russian. Make up five sentences with these phrases.

Column A	Column B
hydrochloric aqueous coiled sand water remedial filter well workover sand chemical radial	filter block acid rig tubing precipitation solution flow intervention production cake work

Ex. 8. The Vocabulary List contains a number of useful terms. Match the terms and their explanations.

a) liner	d) scale removal	h) emulsification
b) filter cake	e) gravel pack	i) radial flow
c) matrix	f) hoist	j) coiled tubing

1. The finer grained, interstitial particles that lie between larger particles or in which larger particles are embedded in sedimentary rocks such as sandstones and conglomerates.

2. A device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps.

3. A casing string that does not extend to the top of the wellbore, but instead is anchored or suspended from inside the bottom of the previous casing string.

4. Metal piping, normally 2,5 to 8 cm in diameter, used for interventions in oil and gas wells and sometimes as production tubing in depleted gas wells.

5. The residue deposited on a permeable medium when slurry, such as a drilling fluid, is forced against the medium under a pressure.

6. The formation of a mixture of two liquids, such as oil and water, in which one of the liquids is in the form of fine droplets and is dispersed in the other.

7. Fine gravel used to surround water borehole screen to act as filter, preventing ingress of particles, silt, sand to borehole.

8. A common well-intervention operation involving a wide variety of mechanical inhibitor treatments and chemical options.

9. The flow of fluids into a wellbore from the surrounding drainage area.

Ex. 9. Insert appropriate items from the box into the following sentences. Sometimes you will have to change the form of the word.

a) workover	g) hydraulic fracturing	m) liner
b) hoist	h) prerequisite	n) slant well
c) surfactant	i) well intervention	o) maintenance
d) bottomhole completion	j) propagate	p) proppant
e) acetic acid	k) solids	q) sand production
f) fluid loss agent	l) matrix	r) formation damage

1. Many models have been developed to investigate the way fractures __________ through rock.

2. These channels were enhanced with HCl instead of __________, resulting in a formation damage removal and permeability improvement.

3. __________ drilling, where the well is drilled at an angle instead of directly vertical, has been around for years, but new technology is allowing for the drilling of tightly curved well holes.

4. Completion and workover fluids invade the producing zone, causing __________.

5. In many cases, __________ implies the removal and replacement of the production tubing string after the well has been killed.

6. Proper choice of candidate wells is a __________ for a successful frac operation.

7. In sandstones, __________ treatments restore or improve the natural formation permeability around the wellbore by dissolving material plugging the pores or by enlarging the pore spaces.

8. Seventy percent of the world oil and gas reserves are contained in sandstone reservoirs where __________ is likely to become a problem at some point during the life of the field.

9. A well servicing unit consists of a __________ and engine mounted on a wheeled chassis, while the workover rig is basically the same.

10. __________ enables the production of natural gas and oil from rock formations deep below the earth’s surface, where there may not be sufficient porosity and permeability to allow natural gas and oil to flow from the rock into the well bore and be recovered.

11. __________ are used to thicken or gel crude oil, light oil, and water or acid fracturing fluids to seal off pores and flow channels in the reservoir matrix.

12. A __________ is any operation carried out on a oil or gas well during, or at the end of its productive life, that alters the state of the well, provides well diagnostics or manages the production of the well.

13. Many openhole completions will incorporate fluid loss valves at the top of the __________ to provide well control whilst the upper completion is run.

14. This __________ is used as a well servicing fluid to remove oil-based mud cakes.

15. __________ materials are carefully sorted for size and sphericity to provide an efficient conduit for production of fluid from the reservoir to the wellbore.

16. The company has developed an assembly for __________, which includes a conduit adapted for installation in a well bore and one or more fluid jet nozzles.

17. Regular __________ work is performed on an oil or gas well to improve or maintain the production from a formation already producing fluids.

18. A typical example of formation damage due to suspended __________ occurs in water injectors.

Ex. 10. Translate the following sentences into English, using vocabulary from the text and terms given at the beginning of the Unit. (The items are underlined.)

1. Компания предоставляет услуги по выполнению кислотного ГРП, матричной кислотной обработке, борьбе с выносом песка.

2. Заканчивание забоя скважины спроектировано с применением противопесочных фильтров, позволяющих остановить проникновение песка без уменьшения скорости потока флюида.

3. Образование эмульсий – типичная проблема при эксплуатации скважин, требующая химической обработки.

4. Если хвостовик для заканчивания обычно спускается с фильтрами или с предварительно проперфорированной трубой, то использование подвески и пакера зависит от условий эксплуатации и отклонения самого хвостовика.

5. Кислотная обработка матрицы – это процесс нагнетания кислоты в пласт под давлением ниже давления гидроразрыва с целью удалить повреждение коллектора (или скин) и восстановить проницаемость до исходной проницаемости пласта-коллектора или повысить ее.

6. Приток зависит от свойств породы, относительной проницаемости и состояния поверхности призабойной зоны.

7. При обработке приствольной зоны скважины в нее закачиваются водные растворы на основе соляной, фтористоводородной и уксусной кислот.

8. При гидравлическом разрыве пласта нефть или вода, смешанные с песком или другим расклинивающим наполнителем, закачиваются в пласт с высокой скоростью, вызывая растрескивание пласта.

9. Основная цель этой операции – очистка поверхности забоя от глинистой корки.

10. Специальные добавки цементного раствора предотвращают его разбухание и образование препятствия на забое.

11. Обработка раствором ПАВ производится с целью разрушения водо-нефтяной эмульсии и очистки от нее пор и трещин в призабойной зоне пластов.

12. Набухание глин в контакте с буровым раствором затрудняет приток флюида к скважине.

13. Для поддержания трещины ГРП в открытом состоянии в кластических коллекторах используется проппант, а в карбонатных – кислота, которая расширяет стенки созданной трещины.

14. Сооружение гравийного фильтра в призабойной зоне предназначено для контроля за выносом песка при эксплуатации скважины в рыхлых и слабоцементированных пластах-коллекторах.

15. Дебит скважины может быть частично восстановлен после удаления зарастания внутренней поверхности.

16. Текущий ремонт скважин должен проводиться с минимальными затратами времени.

17. Было выявлено, что в этой наклонно-направленной скважине повреждения происходят в интервале между пакером ГРП и подвеской хвостовика.

18. Наиболее предпочтительными с экономической точки зрения считаются такие виды КРС, как интенсификационные работы, работы с колтюбинговыми установками, связанные с промывкой песчаных пробок, отложений парафина.

Listening

Ex. 11. Listen to two parts of a talk on well treatment operations, hydraulic fracturing and acid stimulation. Fill in the following table with a short phrase.

Vocabulary:

1. brine – насыщенный солевой раствор

2. aluminum – алюминий

	Hydraulic fracturing	Acid stimulation
Purpose
Active agent(s)
Benefits / dangers of these agents
Reasons for using additives
Most critical parameter involved in the operation		-----

Now, summarize the information given in the video and compare the principles of the two operations described.

Ex. 12. Watch the video about the hydraulic lift system manufactured by Volcanica Energy company and decide, whether the following statements are true or false.

Vocabulary:

1. artificial lift – механизированная добыча

2. pressurized – находящийся под давлением

3. power fluid – напорная жидкость

4. prime mover – первичный привод

5. jet pump – струйный насос

6. ancillary equipment – вспомогательное оборудование

7. separation package – установка сепарирования

8. multiplex plunger pump – многоканальный поршневой насос

9. psi – фунт на квадратный дюйм (ед.изм. давления)

10. Venturi principle – принцип Вентури

11. nozzle throat – сечение сопла

12. entrained gas – увлеченный газ

13. gas-liquid ratio – газожидкостный фактор

14. specific gravity – удельная плотность

15. water cut – обводненность

16. hydrostatic head – давление столба жидкости, водяной напор

17. commingling – совместный

18. cavity – полость

19. bottom-hole assembly – компоновка низа бурильной колонны

20. carbide – карбидный

1. Most wells are produced with artificial lift equipment.

2. Many types of artificial lift employ electrical or mechanical principles of connection between surface and subsurface equipment.

3. The hydraulic lift system consists of four pumps.

4. The surface pump can be driven be an electrical motor.

5. Power fluid travels from the surface down the well and back to the surface.

6. Jet pump is located at the wellhead.

7. Volcanica jet pump is flexible in terms of the depth and well design.

8. The deeper the well, the greater pressure is needed for fluid intake.

9. The jet pump is always repaired at an authorized shop.

10. One of the advantages of the Volcanica jet pump is that it does not come in contact with entrained gases.

11. Volcanica jet pump is energy-efficient.

Grammar

Ex. 13. Study the following information.