Eight Steps Ensure Successful Cement Jobs



In completion of oil and gas wells, cement isolates the wellbore, prevents casing failure and keeps wellbore fluids from contaminating fresh water aquifers. The basic factors engineer and operators must consider fro successful cementing jobs have not changed in more than 50 years. These factors are as following:

  1. condition the drilling mud
  2. use spacers and flushes
  3. move the pipe
  4. centralize the casing
  5. maximize the displacement rate
  6. design slurry for proper temperature
  7. select and rest cement compositions
  8. select a proper cementing system

 

 

1. Condition the drilling mud is the most important variable in achieving good displacement during a cement job. To condition the drilling mud in preparation for a cement job, the following measures are necessary to follow:

    • determine the hole volume that can be circulated; evaluate the % of wellbore that is actually being circulated ( for best results, use a caliper or material balance to determine downhole fluid mobility and check for annular fluid that is not moving);
    • circulate the drilling mud to help break the gel structure of the fluid; condition the drilling mud until equilibrium is achieved ( after casing is on bottom and before the displacement begins, circulating the mud decreases its viscosity and increases mobility);
    • never allow the drilling mud to set static for extended periods, especially at elevated temperatures. (mud properties coming out of the well are the same as the mud pumped in); continue circulating until displacement program begins;
    • modify the flow properties of the drilling fluid to optimize mobility and drilling cuttings removal;
    • examine the mud gel strength profile during the job planning stage and just before the cement job (an optimum drilling fluid will have flat, non progressive gel strengths);
    • measure the gel strength development during the job planning stage, at downhole temperature and pressure.

 

2. Spacers, flushes are effective mud displacement aids. They separate the dissimilar drilling mud from the cement. Spacers enhance gelled-mud removal and allow better cement bond with the borehole. Spacers are designed to serve various needs: (1) help well control; (2) provide increased mud-removal benefits. The following guidelines should be considered to achieve maximum mud displacement:

  • pump the spacer fluid at an optimized rate or as fast as possible without breaking down the formation;
  • provide spacer contact time and volume to remove the greatest possible amount of mud;
  • make sure the viscosity, yield point and density of both the spacer and the cement slurry, are at least the same as the drilling fluid;
  • design the spacer package to water-wet the surface of the pipe and formation thoroughly when using oil-based or synthetic – based drilling fluids.

 

Flushes are used for thinning and dispersing drilling – fluid particles. These fluids go into turbulence at low rates, helping to clean drilling fluid from the annulus. Flushes generally have densities close to water and may not provide proper well control. Some chemical flushes (oxidizers, sodium silicate-based fluids) aggressively attack specific drilling muds, breaking them down and further enhancing drilling fluid removal.

 

3. Move the pipe:

  • rotating and reciprocating casing before and during cementing breaks up stationary, gelled pockets of drilling mud;
  • loosens cuttings trapped I the gelled mud
  • allows high displacement efficiency at lower pump rates by keeping the drilling mud flowing.

The industry has not specified minimum requirements for pipe movement during cement.

 

4. Centralize: centralizing casing with mechanical centralizers across the intervals to be isolated helps optimize drilling –fluid displacement. Good pipe standoff helps ensure uniform flow patterns around the casing. Equalizing the friction loss or force that flowing cement exerts around the annular clearance increases drilling-fluid removal. The best mud displacement at optimum rate is achieved when annular clearance is 1-1.5in. Pipe movement and displacement are severely restricted. Centralizers and other mechanical cementing aids commonly used in the industry, also serve as inline laminar flow mixers. They change flow patterns and promote better mud displacement and removal.

 

5. Displacement rate:

  • high-energy flow in the annulus is most effective to ensure good mud displacement;
  • turbulent flow around the full casing circumference is desirable, but not absolutely essential;
  • when turbulent flow is not a viable option for the formation or wellbore configuration, the highest pump rate is feasible;
  • the best cementing results are obtained when the spacer and cement are pumped at maximum energy, the spacer s appropriately designed to remove mud and good competent cement is used.

 

6. Proper temperature

One can optimize cost and displacement efficiency by following guidelines:

  • design the job on basis of actual wellbore circulating temperatures;
  • estimate the bottomhole circulating temperature (BHCT) using the API;
  • use the actual downhole temperatures measured;
  • include surface mixing time when estimating job time.

 

7. Cement composition Operators are encouraged to design cement slurry for its specific application, with good properties to allow placement in a normal time period. The ideal cement slurry has no measurable, free water, provides adequate retarder to ensure proper placement and maintains stable density to ensure hydrostatic control. Several criteria affect slurry design:

  • well depth
  • BHCT
  • Bottomhole static temperature (BHST)
  • Drilling fluid hydrostatic pressure
  • Drilling fluid type
  • Slurry density
  • Lost circulation
  • Gas migration potential
  • Pumping time
  • Quality of mix water       fluid-loss control
  • Flow regime
  • Settling and fre water
  • Quality of cement
  • Dry or liquid additives
  • Strength development
  • Quality of the cement testing laboratory and equipment.

 

8. Cementing system selection – Operators select cement systems on the basis of job objectives and well requirements. Cement is basically inelastic. Cementing systems are similar in many ways. These systems vary in their capability to provide good zone isolation in changing environments. The traditional approach to cement selection has been on the basis that higher compressive strengths result in higher cement sheath quality. One of the most versatile systems to apply is foam cement, which produces a more ductile and resilient cement and withstands the stress associated with casing expansion and contraction.

 

 

     Annular fluid removal

                                                          

                                              

Centralize pipe (centralizing the pipe is important to obtain high displacement efficiency)
 Move pipe (pipe movement –  rotating or reciprocating- both during and after cementing, is second in importance only to drilling fluid conditioning)                                                                                                            

                                                                     

Fluid loss (if fluid loss is controlled, cement can contact the entire interval, allowing small nodes of dehydrated cement to build up across permeable areas of interest before squeeze pressure develops)

Low fluid loss              Uncontrolled fluid loss

Primary cementing (highly permeable sections require good

fluid – loss control in primary cementing)

 

 

Fluid loss (uncontrolled fluid loss can result

in rapid cement dehydration)

 

Spacers and flushes (spacers and flushes are effective displacement aids.

They separate the dissimilar cement and drilling mud.

Spacers enhance gelled mud removal allowing a better cement bond.)

 

contaminate загрязнять
casing failure Разрушение обсадных труб
spacer(s) Промежуточное кольцо (жидкость с высокой вязкостью и плотностью для удаления бурового раствора)
flush(es) Струя жидкости
displacement rate Объемный расход
slurry Цементный раствор
drilling fluid Буровой раствор (промывочная буровая жидкость)
fluid mobility Подвижность жидкости
hole volume Объем скважины
annular space Затрубное пространство
elevated temperature Надземная \ поверхностная температура
drill cuttings шлам
inclination Угол наклона буровой скважины к горизонту
fluid removal Смещение жидкости (отвод жидкости)
gelled mud Густой буровой раствор
bond (bonding) соединение
weighted spacer утяжелитель
compatibility совместимость
contact time Время контакта
yield point Предел текучести
water wet смачиваемость
disperse диспергировать
flow path Пути проникновения потока
surge pressure Гидравлический удар (давление)
swab (pressure) Поршень для откачки из скважины
equivalent circulating density (ЕCD) Эквивалент циркуляционной плотности
reciprocating Расхаживание труб
casing head pressure Давление на устье скважины
centralizer Центратор- для центрирования колонн обсадных труб
standoff Степень центрирования (обсадной колонны в стволе)
friction loss Потери на трении
annular clearance Затрубный интервал
laminar flow Ламинарное течение
flow pattern Структура потока
casing circumference Окружность обсадных труб
set time Установленное время
thickening time Время загустевания цементного раствора
compressive strength Предел прочности при сжатии
downhole (bottomhole) Забойное давление
retarder Замедлитель реакции \ демпфер
bottomhole circulation temperature (BHCT) Динамическая температура на забое
bottomhole static temperature (BHST) Статическая температура на забое
cement sheath Фильтрационная корка на стенках скважины
foam cement Цементная пена
expansion расширение
contraction сжатие
ductile Пластичный вязкий
resilient Упругий \ эластичный

 

                                   Установка вращательного бурения

                                              Rig Components

1. Gin pole козлы
2. Crown block кронблок
3. Derrick вышка
4. Traveling block Талевый блок
5. Swivel bail Серьга вертлюга
6. Swivel вертлюг
7. Rotary hose, safety chain Предохранительная цепь бурового шланга
8. Goose neck Горловина вертлюга
9. Stand pipe Стояк
10. Rotary hose Буровой шланг
11. Derrick leg Нога вышки
12. Mouse hole Шурф для двухтрубки
13. Derrick floor Пол вышки
14. Base plate Основание ноги привода ротора
15. Guard, rotary drive Ограждение цепи привода ротора
16. Line, fill-up Линия для закачивания бурового раствора в скважину
17. Steps лестница
18. Substructure , ramp Наклонная площадка
19. Derrick substructure Подвышечное основание
20. Rathole Шурф для квадрата
21. Hydraulic brake Гидродинамический тормоз
22. Surge chamber компенсатор
23. Substructure, drawworks Основание под буровую лебедку
24. Compound Трансмиссия
25. Platform, engine Площадка у двигателей
26. Guard, pump drive Ограждение привода насосов
27. Slush pump Буровой насос
28. Mud line manifold Обвязка буровых насосов
29. Mud mixing hopper Воронка для приготовления бурового раствора
30. Water supply line водопровод
31. Suction line Приемная линия буровых насосов
32.  Suction tank Приемная емкость
33. Mud gun, fixed Стационарная струйная насадка для размешивания бурового раствора
34. Mud tank, connections Соединения емкостей
35. Air chamber Воздушная емкость
36. Settling pit Отстоечная емкость
37. Mud gun, movable Передвижная струйная насадка для размешивания бурового раствора
38. Shale shaker Вибрационное сито
39. Engines, drilling Буровые двигатели
40. Guard, drive chain Ограждение цепной передачи
41. Mud return ditch Желоб для бурового раствора
42. Drawworks Буровая лебедка
43. Rotary table ротор
44. Girt Пояс вышки
45. Kelly Квадратная штанга (квадрат)
46. Derrick brace Крест вышки
47. Rotary hook Подъемный крюк
48. Runaround Балкон вышки
49. Line, rotary Талевый канат
50. Mud return line Линия для выхода бурового раствора
51. Casing head Устьевое оборудование
52. Blowout preventer Противовыбросовая задвижка (превентер)
53. Cross tee крестовик

 


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