Unit 12 casing and cementing

 

12.1. Remember the meaning of the following words and word-combinations:

 

attempt – пытаться, пробовать

either …. or – или...или, либо …. либо

hole collapsing – обрушение скважины

blowout = uncontrolled flow of oil or gas – внезапный выброс, фонтан

from time to time – время от времени, периодически

safeguard – предохранять, защищать

casing – обсадные трубы, обсадная колонна; крепление (скважины)

обсадными трубами

cement in place – цементировать на месте

conductor – кондуктор (первая колонна обсадных труб)

surface casing – кондуктор

production casing – эксплуатационная обсадная колонна

liner – нижняя труба обсадной колонны, хвостовик

clamp with a packer – зажимать с помощью пакера

extend – протягиваться, проходить

casing joint – соединение обсадных труб

expected loads – ожидаемые нагрузки

collapse load – разрушающая нагрузка

cement slurry – цементное тесто, цементный раствор

be exposed to smth. – подвергаться ч-л

burst load – разрывающая нагрузка

tension load – растягивающая нагрузка

corrosion service – техническое обслуживание с учетом коррозии

buckling resistance – сопротивление продольному изгибу

running casing – спуск обсадной колонны

screw together – завинчивать до отказа

guide shoe – направляющий башмак

bottom – забой (скважины)

one way valve – клапан, открывающийся в одну сторону

displace upwards – вытеснять\ выдавливать\ выталкивать вверх

float collar – 1. обратный клапан 2. муфта обсадной трубы с обратным

клапаном

bottom plug – пробка на забое

rubber seal = plug – пробка

prevent contamination – предотвращать загрязнение

bond – 1. сцепление, соединение 2. связующее \ цементирующее вещество

annulus – затрубное пространство

turbulent flow – турбулентный \ вихревой поток

laminar flow – ламинарный поток

place evenly – распределять равномерно

prevent entering – предотвратить попадание (цементного раствора)

centralizer = steel string – центратор

wait on cement (time) = WOC – время ожидания затвердевания цемента

prevent buckling – предотвратить изгиб

permeable formation – проницаемый пласт

seal off trouble horizons – изолировать проблемные зоны

lost circulation zone – зона потери циркуляции

perforation – перфорация

additives – добавки

avoid unnecessary delays – избегать ненужных задержек

withstand – выдерживать

spacer fluid – буферная жидкость; разделяющая жидкость

ahead of – впереди, перед ч-л

mudcake – глинистая корка

12.2. Read and translate the text using a dictionary:

 

CASING AND CEMENTING

 

Imagine that a reservoir is at a depth of 2500m. We could attempt to drill one straight hole all the way down to that depth. That attempt would end either with the hole collapsing around the drill bit, the loss of drilling fluid into formations with low pressure, or in the worst case with the uncontrolled flow of gas or oil from the reservoir into unprotected shallow formations or to the surface (blowout). Hence, from time to time, the borehole needs to be stabilized and the drilling progress safeguarded. This is done by lining the well with steel pipe (casing) which is cemented in place. In this manner the well is drilled like a telescope (Fig. 16) to the planned total depth (TD). The diameters of the ‘telescope joints’ will start usually with a 23" (conductor), then 18 5/8"(surface casing), 13 3/8" (intermediate casing above reservoir), 9 5/8" (production casing across reservoir section) and possibly 7" ‘ li’ ' over a deeper reservoir section. A liner is a casing string which is clamped with a packer into the bottom part of the previous casing; it does not extend all the way to the surface, and thus saves cost. Casing joints are available in different grades, depending on the expected loads to which the string will be exposed during running, and the lifetime of the well.

The main criteria for casing selection are:

Collapse load: originates from the hydrostatic pressure of drilling fluid, cement slurry outside the casing and later on by ‘moving formations’, e.g. salt;

Burst load: This is the internal pressure the casing will be exposed to during operations;

Tension load: Caused by the string weight during running in; it will be highest at the top joints;

 

Figure 16. Casing scheme.

 

Corrosion service: Carbon dioxide (CO2) or hydrogen sulphide (H2S) in formation fluids will cause rapid corrosion of standard carbon steel and special steel may be required;

Buckling resistance: The load exerted on the casing if under compression.

The casing will also carry the blowout preventers described earlier.

Running casing is the process by which 40 foot sections of steel pipe are screwed

together on the rig floor and lowered into the hole. (Fig. 17).

The bottom two joints will contain a guide shoe, a protective cap which facilitates the downward entry of the casing string through the borehole. Inside the guide shoe is a one way valve which will open when cement/mud is pumped down the casing and is displaced upwards on the outside of the string. To have a second barrier in the string, a float collar is inserted in the joint above the guide shoe. The float collar also catches the bottomplug and top plug between which the cement slurry is placed. The slurry of cement is pumped down between the two rubber seals (plugs). Their function is to prevent contamination of the cement with drilling fluid which would cause a bad cement bond between borehole wall and casing. Once the bottom plug bumps into the float collar it ruptures and the cement slurry is pushed down through the guide shoe and upwards outside the casing. Thus the annulus between casing and borehole wall is filled with cement. The success of a cement job depends partly on the velocities of the cement slurry in the annulus. A high pump rate will result in turbulent flow which results in a better bond than the slower, laminar flow.

 

Figure 17. Principle of casing cementation.

 

The cement has to be placed evenly around each casing joint. This becomes more difficult with increasing deviation angle since the casing joints will tend to lie on the lower side of the borehole preventing cement slurry entering between casing and borehole wall. To avoid this happening steel springs or centralizers are placed at intervals outside the string to centralize the casing in the borehole.

Once the cementation has been completed the rig will ‘ wait on cement’(WOC), i.e. wait until the cement hardens prior to running in with a new assembly to drill out the plugs, float collar and shoe, all of which are made of easily drillable materials.

The process described so far is called a primary cementation, the main purpose of

which is to:

· bond the casing to the formation and thereby support the borehole wall;

· prevent the casing from buckling in critical sections;

· separate the different zones behind the casing and thereby prevent fluid;

movement between permeable formations;

· seal off trouble horizons such as lost circulation zones.

Sometimes primary cementations are not successful, for instance if the cement volume has been wrongly calculated, if cement is lost into the formation or if the cement has been contaminated with drilling fluids. In this case a remedial or secondary cementation is required. This may necessitate the perforation of the casing a given depth and the pumping of cement through the perforations.

The chemistry of cement slurries is complex. Additives will be used to ensure the slurry remains pumpable long enough at the prevailing downhole pressures and temperatures but sets (hardens) quickly enough to avoid unnecessary delays in the drilling of the next hole section. The cement also has to attain sufficient compressive strength to withstand the forces exerted by the formation over time. A spacer fluid is often pumped ahead of the slurry to clean the borehole of mudcake and thereby achieve a better cement bond between formation and cement.

 

12.3. Give English equivalents for the following phrases. Use the text:

Потеря буровой жидкости в пластах с низким давлением; в худшем случае; следовательно; таким образом; проектная глубина; промежуточная обсадка выше коллектора; он (хвостовик) не доводится до поверхности; в зависимости от ожидаемых нагрузок; во время эксплуатации скважины; главные критерии; подвижные пласты; вызываемая весом колонны при спуске; обычная углеродная сталь; нагрузка, оказываемая на обсадную колонну при сжатии; секции стальной трубы, длинною 40 футов; защитный колпак, облегчающий спуск обсадной колонны; обратный клапан вставляется в стык выше направляющего башмака; который вызовет плохое сцепление между стенками скважины и обсадной колонной; как только; частично зависит от скорости; при увеличении угла отклонения; если цемент загрязнен буровым раствором; чтобы гарантировать; должен достичь достаточного сопротивления сжатию.

 

12.4. Insert the missing prepositions: in (4), of (2), at (1), from (1), with (2), on (3), to (2), by (1):

 

1) The attempt to drill one straight deep hole would end ………. the hole collapse.

2) The well is stabilized with a casing which is cemented ……….. place.

3) In this manner the well is drilled like a telescope ………… the total depth.

4) Grades of casing joints depend ………. the expected loads ………. which the string will be exposed during running.

5) Buckling resistance is the load exerted ………. the casing if under compression.

6) Running casing is the process ……….. which sections of steel pipe are screwed together and lowered into the hole.

7) The success ……. a cement job depends …….. the velocities …… cement slurry …….. the annulus.

8) Centralizers are placed …….. intervals outside the string to centralize the casing …….. the borehole.

9) One of the purposes of primary cementation is to prevent the casing ………. buckling …….. critical sections.

10) A secondary cementation is required if the cement has been contaminated ………. drilling fluids.

 

12.5. Match the words in A with their definitions in B and translate them into Russian:

A B

1) collapse load a) the load exerted on the casing if under

compression

2) burst load b) uncontrolled flow of oil or gas from the

reservoir

3) tension load c) a protective cap which facilitates the down-

ward entry of casing string through the hole

4) buckling resistance d) substances that are used to ensure the

slurry remains pumpable long enough

5) running casing e) the load that originates from the hydrostatic

pressure of drilling fluid, cement slurry

outside the casing

6) guide shoe f) the process by which sections of steel pipe

are screwed together on the rig floor and

lowered into the borehole

7) centralizers g) internal pressure the casing will be exposed

to during operations

8) WOC h) steel strings that are placed at intervals

outside the string to centralize the casing

9) additives i) the load caused by the string weight during

running in

10) blowout j) wait time until cement hardens

 

12.6. Answer the following questions on the text:

1) What is casing? 2) Why is casing necessary? 3) Give the names and usual diameters of the ‘telescope joints’. 4) What are the main criteria for casing selection? 5) What is running casing? 6) Why is the guide shoe necessary? 7) What is the function of the two rubber seals (plugs)? 8) What does the success of a cement job depend on? 9) What is the function of centralizers? 10) What happens after the cementation has been completed? 11) What is the purpose of a primary cementation? 12) What happens if primary cementation is not successful? 13) What is a secondary cementation? 14) Why are additives used in cement slurries? 15) What is the function of a spacer fluid?

 

12.7. Translate the paragraph beginning with “Running casing …” in writing.

12.8. Make up sentences using the following words:

 

a.in pipe lined is place well is a steel with The called cemented casing which.

b. The cementation completed assembly been with the rig until the having hardens prior to waits running in a new cement.

 

12.9. Render the text “Casing and Cementing” in Russian.