Annular BOP / Ram BOP / Rotating BOP / Shear Ram BOP

A blowout preventer is a required well-control device for downhole operations and plays a very important role in preventing and handling blowouts. The following sections focus on BOP classification, technical parameters, structure, working principles, operation, maintenance and troubleshooting.

1. Classification and Naming of Blowout Preventers

1. Classification

Blowout preventers are divided into two main categories: Annular BOP and Ram BOP.

Annular BOPs are divided into single Annular BOP and double Annular BOP. They are equipped with one annular packing element or two annular packing elements respectively.

Ram BOPs are divided into single Ram BOP, double Ram BOP and triple Ram BOP. They are equipped with one pair, two pairs or three pairs of rams respectively, so that different pipe strings and open hole can be sealed.

2. Codes

The BOP code is composed of the first pinyin letters of the main Chinese characters in the BOP name, as shown in Table 1.

Table 1. BOP codes

Note: FH indicates an Annular BOP with a spherical packing element.

FHZ indicates an Annular BOP with a tapered packing element.

3. Basic parameters

The nominal bore and maximum working pressure of a BOP should comply with Table 2.

Table 2. Nominal bore and maximum working pressure of BOP

Note: the limit deviation of the drift gauge diameter is +0.25 to 0 mm. Its length should be greater than the bore by 50 mm and not shorter than 300 mm.

4. Naming

Model designation: maximum working pressure in MPa, bore code, and product code.

Example: for a double Ram BOP with a bore of 346.1 mm and a maximum working pressure of 70 MPa, the model is expressed as 2FZ35-70.

API BOP code designations:

R - single Ram BOP, which may be a blind Ram BOP or a pipe Ram BOP.

Rd - double Ram BOP.

Rt - triple Ram BOP.

A - Annular BOP.

G - Rotating BOP.

M - working pressure of 1000 psi.

Cn - remote hydraulic connector installed between the BOP stack and the wellhead or between BOPs, with maximum working pressure equal to the BOP stack, used for subsea wellheads.

Cv - low-pressure remote hydraulic connector installed between the riser and the BOP stack, used for subsea wellheads.

Example: a certain well-control equipment code is 5M-13 3/8-SRdA. Here 5M indicates a rated working pressure of 5000 psi; 13 3/8 indicates the bore size; SRdA indicates, upward from the permanent wellhead, spool plus double Ram BOP plus Annular BOP.

2. Annular BOP

An Annular BOP is also called a multi-function BOP. When closing the well, the annular packing element is squeezed uniformly toward the center of the wellbore. It has the advantages of high pressure capacity, reliable sealing, convenient operation, and fast opening and closing. It is especially suitable for sealing pipe strings of different types and sizes, and it can also fully close the wellhead.

Annular BOPs can be divided into tapered packing element, spherical packing element and cylindrical packing element types.

1. Tapered packing element Annular BOP

1) Structure

A tapered packing element BOP is mainly composed of body, support sleeve for the packing element, piston, packing element, top cover, dust ring, bolts, cover plate, lifting ring, retaining ring, upper connector and lower connector. The structure is shown in Figure 1.

1. Top cover; 2. packing element; 3. dust ring; 4. piston; 5. body

Figure 1. Tapered packing element Annular BOP structure

Tapered packing element Annular BOP

2) Working principle

During use, the BOP is hydraulically operated. Pressure oil from the hydraulic system enters the cylinder through the lower connector on the body and pushes the piston upward. The tapered surface of the piston squeezes the packing element, while the top surface of the packing element is limited by the top cover. The packing element contracts radially and grips the pipe string, or fully seals the bore when no pipe string is in the well. To open the BOP, the hydraulic system is operated so that pressure oil enters the upper cylinder from the upper connector while oil in the lower cylinder returns. The piston moves downward, and the packing element gradually returns to its original shape under elasticity, opening the wellhead. The closing time of this BOP is generally not more than 30 seconds, while opening takes slightly longer.

2. Spherical packing element Annular BOP

A spherical packing element BOP is mainly composed of top cover, packing element, piston, body, coupling ring and sealing rings. Its structure is shown in Figures 2 and 3.

Figure 2. Spherical packing element Annular BOP structure (1)

Spherical packing element Annular BOP

Figure 3. Spherical packing element Annular BOP structure (2)

Spherical packing element Annular BOP structure

During closing, pressure fluid in the lower oil chamber, the closing chamber, pushes the piston rapidly upward. The packing element is forced along the spherical inner cavity of the top cover, squeezed and gathered from bottom to top and from the outer edge toward the center, so that the well is sealed. During opening, pressure oil in the upper oil chamber, the opening chamber, pushes the piston downward. The squeezing force on the packing element disappears, and the rubber elasticity quickly restores the element to its original shape, opening the wellhead.

High-pressure wellhead fluid acts in the annular groove above the piston and forms an upward force that helps the piston lift and squeeze the packing element to close the well. Therefore, well pressure assists sealing in a spherical packing element Annular BOP.

The spherical packing element has a large diameter and relatively low height. It has 12 to 20 support ribs, stores more rubber, and has a longer service life than a tapered packing element. The bottom of the support ribs is made as a circular curved surface to ensure good contact between the bottom of the packing element and the top of the piston.

Like the tapered packing element, the spherical packing element can be replaced at the well site. When there is pipe string in the well, the old element can also be removed by cutting and replaced with a new one. Unlike a tapered packing element, the service life of a spherical packing element cannot be checked in the field.

The overall structure of a spherical packing element Annular BOP is short and wide. The distance between the upper and lower sealing support positions of the piston is small, so the guiding and centering effect is poor. Near the end of the closing stroke, the piston support distance becomes even smaller, and the piston is prone to eccentric wear. If the hydraulic oil is not clean, solid particles may enter the clearance between piston and body, easily causing piston sticking or cylinder scoring. A spherical packing element Annular BOP therefore requires high cleanliness of hydraulic control oil, and the hydraulic oil should be filtered and replaced on schedule.

3. Cylindrical packing element Annular BOP

A cylindrical packing element Annular BOP is mainly composed of upper body, packing element, sealing ring, protective ring and lower body. High-pressure oil is located between the body and the rubber cylinder. The rubber cylinder seals tubing and similar pipe strings. There is only one oil port, and a three-position four-way reversing valve is used for oil inlet and outlet. The structure is shown in Figure 4.

Figure 4. Cylindrical packing element Annular BOP structure

Cylindrical packing element Annular BOP structure

1. M30 x 3 nut; 2. M30 x 3 x 190 stud; 3. upper body; 4. packing element; 5. bore sealing ring; 6. protective ring; 7. O-ring; 8. lower body; 9. packing-element skeleton

The cylindrical packing element Annular BOP has simple structure, small size, light weight and high hydraulic-pressure requirement. It is suitable for low-pressure live-well operations such as paraffin scraping, sand washing, small-tubing sealing and cable sealing.

Daily maintenance: the main wearing parts are the rubber cylinder and rubber-cylinder sealing ring. After each well operation is completed, the rubber cylinder wear should be checked promptly. When more than two thirds of the cylinder thickness has worn away, it should be replaced in time.

Technical parameters:

(1) Rated working pressure: 14 MPa.

(2) Hydraulic operating pressure: actual working pressure plus 0.5 MPa.

(3) Working medium: crude oil, water and workover fluid.

(4) Sealing tubing range: 1 1/2 to 4 1/2 in.

3. Ram BOP

The Ram BOP is a key part of well-control equipment. It is mainly used to control wellhead pressure during workover, well testing and maintenance operations, effectively preventing blowout accidents and supporting safe operations. It can perform the following operations:

(1) When there is pipe string in the well, the annular space between casing and tubing string can be sealed with rams of the corresponding size.

(2) When there is no pipe string in the well, the wellbore can be fully closed with blind rams.

(3) Under shut-in conditions, circulation, choking, flowback, well killing and well washing can be carried out through the Kill Manifold and Choke Manifold connected to the side outlet of the spool.

(4) It is used together with Choke Manifold, Kill Manifold and related equipment.

Used in combination, the equipment can control bottomhole pressure and support near-balanced workover.

According to the control method, Ram BOPs are divided into hydraulic Ram BOPs and manual Ram BOPs. According to the number of ram cavities, they are divided into single Ram BOP, double Ram BOP and triple Ram BOP.

1. Hydraulic Ram BOP

Generally speaking, a manual Ram BOP can only be used to prevent blowout, not to stop a blowout. When the wellhead flowing pressure reaches more than 5 MPa, the screw can no longer be turned manually to close the rams. A hydraulic BOP must be operated remotely and closed rapidly within several seconds. Using a hydraulic BOP requires a matching hydraulic control device, high-pressure hoses, quick couplings and related equipment.

According to cavity shape, BOPs have circular, rectangular and oval cavities. A circular cavity has reasonable stress distribution and good machinability, but has large height, large weight and relatively poor sealing. A rectangular cavity, generally used for cast-steel bodies, has low height and good sealing, but cast-steel bodies have inferior material quality, possible porosity and sand holes, stress concentration at the four corners and lower pressure strength. An oval cavity, generally used for forged BOPs, has low height, reasonable stress distribution, light weight and good sealing, but is difficult to machine. According to upper and lower connection type, BOPs can be upper and lower flange type, upper studded lower flange type, upper flange lower studded type, upper and lower studded type, upper and lower clamp type, threaded connection type, or union-head type. The connection type should be selected by the user according to actual field conditions. BOP bodies are made of cast steel or forged steel, and the material should comply with national standards.

The hydraulic oil passages of hydraulic BOPs are generally internal, preventing collision damage. Exposed oil passages have basically been eliminated. Hydraulic BOP side-door opening methods include hinged-seat type, non-hinged type and hydraulic-cylinder opening type.

When selecting upper and lower flange dimensions for manual SFZ18-35 and hydraulic FZ18-35 BOPs, note the following: (1) for common use on 250-type and 350-type wellheads, select a 480 mm diameter flange with double-row hole structure and a special steel ring. (2) For use on a 350-type wellhead, select a 480 mm diameter flange with single-row holes. (3) For matching with a standard 18-35 spool, select a 395 mm diameter flange. (4) For use alone on a 250-type wellhead, select a 380 mm diameter flange and thicken it according to the 35 MPa pressure class.

1) Basic structural composition of hydraulic Ram BOP

Structurally, a hydraulic Ram BOP consists of body, ram assembly, cylinder and piston assembly, side-door assembly, locking device and related parts.

(1) Body. The body is cast from alloy steel and has upper and lower vertical through bores and side holes. There are ram cavities inside the body, and the number of ram cavities depends on the number of rams. The body ram cavity adopts an oblong shape to reduce stress concentration. The upper surface of the ram cavity is a sealing surface and should be protected from damage. At the bottom of the ram cavity there is a sand-settling groove inclined toward the wellbore. It can automatically remove mud and sand when the rams open and close, reduce friction resistance during ram movement, and help well pressure assist ram sealing. Hydraulic oil passages are embedded in the body, simplifying the external structure of the Ram BOP and avoiding damage to oil passages during installation, transportation and use. High-pressure-class BOPs have hinge seats on the body for fixing side doors.

Above the Ram BOP body is a flange, or studded hole, connected by studs to an Annular BOP or directly to a flow tube. Below the body is a flange connected to the spool by studs.

(2) Ram assembly. The ram assembly is mainly composed of top seal, front seal and ram body, as shown in Figures 5 and 6.

1. Ram body; 2. top seal; 3. front seal; 4. ram body; 5. top seal

Figure 5. Pipe ram assembly

Pipe ram assembly

Figure 6. Shear ram body

Shear ram body

The ram is an oblong integral type. Its rubber packer uses an assembled front-seal and top-seal structure. The front seal and top seal can be replaced separately according to their damage condition, and removal and installation are simple and labor-saving. The structure of the ram front seal and top seal rubber is shown in Figure 7.

Figure 7. Ram front seal and top seal rubber

Ram front seal and top seal rubber

The ram rubber can be replaced after wear. When the downhole pipe-string size changes, pipe rams should also be replaced. When changing the size of pipe rams, a double-sided ram may retain the ram body and only replace the pressure block and rubber; a single-sided ram requires replacing the whole ram assembly. The upper and lower surfaces of the rubber in a double-sided ram are symmetrical. When the upper surface is worn during use, the lower surface will also be scratched, so the rubber of a double-sided ram cannot be turned over and reused.

The ram uses floating sealing. There is a certain clearance between the ram assembly and the body cavity where the ram is installed, allowing the ram to float up and down in the body cavity. The upper ram rubber does not contact the top sealing surface of the chamber. When the ram is closed, the high support rib at the bottom of the ram chamber and the top sealing surface both have gradual slopes, ensuring sufficient clearance between ram and body before reaching the sealing position. During sealing, the front rubber of the ram first contacts the pipe string in the well and seals tightly around it under piston thrust. When the ram opens, the top sealing rubber leaves the body shoulder surface and retracts into the ram plane, and the ram retreats along the support-rib slope to the fully open position. This floating feature ensures reliable sealing, reduces opening and closing resistance and rubber wear, extends ram service life, prevents rust seizure between body and ram, and makes disassembly easier.

When a pipe string is in the wellbore and a Ram BOP is used to shut in the well, the pipe string is usually not exactly centered in the bore and often leans to one side. The pipe string may therefore be caught by the ram and fail to seal. To solve pipe centering, a protruding guide block and corresponding groove are made at the front of the ram pressure block. When the rams move toward the wellbore center, the guide block forces the eccentric pipe toward the center, allowing smooth sealing. After shut-in, the guide block enters the groove of the opposite pressure block, as shown in Figure 8.

Figure 8. Ram automatic centering schematic

Ram automatic centering schematic

(3) Cylinder and piston assembly. This assembly consists of cylinder, piston, piston rod, cylinder cover and related parts.

(4) Side-door assembly. A Ram BOP has detachable or swing-open side doors. Normally the side doors are fastened to the body with bolts. Piston-rod seals and side-door-to-body seals are installed on the side doors. The side doors must be opened when replacing rams, replacing piston-rod seals, inspecting rams or cleaning ram chambers.

(5) Locking device. The locking device has two functions: first, when hydraulic control fails, the rams can be closed manually; second, after hydraulic shut-in, the rams can be fixed mechanically and the high pressure in the hydraulic control oil can be released, avoiding long-term shut-in leakage of hydraulic oil lines and preventing misoperation accidents.

Ram locking devices are divided into manual ram locking devices and hydraulic locking devices, also called automatic locking devices.

Manual locking device:

When the hydraulic control system fails, manual operation can close the rams. The manual ram locking device is shown in Figure 9. It consists of locking shaft, piston shaft and manual-control assembly.

(a) Locked state; (b) unlocked state

Figure 9. Manual ram locking device

Manual ram locking device

The manual locking device relies on manual rotation of the handwheel to drive the locking shaft and lock the rams. Its function is to lock the rams in the closed position after hydraulic closing when long-term shut-in is required, after which hydraulic pressure can be bled off. After the rams are closed hydraulically, turn the handwheel to the right for manual locking. The operating rod drives the locking shaft to rotate. Because the ram shaft cannot rotate or move forward, the locking shaft retreats until its shoulder bears against the cylinder cover, locking the rams.

The manual locking device can only close the rams and cannot open them. To open rams that have been manually locked, the manual locking device must first be reset and unlocked, and then the rams must be opened hydraulically. This is the only method. The specific operation is: first turn the handwheel to the left until it stops, then turn back 1/8 to 1/4 turn to prevent the locking shaft from jamming in the unlocked position due to temperature change, then open the rams hydraulically.

Automatic locking device:

The automatic locking device of a Ram BOP is still a mechanical locking mechanism, but ram locking and unlocking are both completed by hydraulic pressure, so it is often called a hydraulic locking device.

Its operating feature is that after the Ram BOP closes by hydraulic pressure, the ram locking action is automatically completed under hydraulic control oil pressure. Conversely, when the Ram BOP opens hydraulically, the ram unlocking action is first completed automatically under hydraulic pressure, and then hydraulic opening occurs.

A hydraulic locking device cannot close the well manually. If hydraulic control fails, a Ram BOP equipped only with this device cannot perform a closing action.

Ram BOPs with hydraulic locking devices are often used offshore. In offshore operations, the BOP is often installed on the seabed, so ram locking and unlocking cannot be performed manually and must be performed by hydraulic remote control.

2) Sealing of hydraulic Ram BOP

The essence of Ram BOP sealing is to use rubber products that deform greatly under load, fit uniformly against the sealed surface, prevent leakage, and restore after external force is removed. According to sealing position and shape of the sealing body, rubber sealing parts of different shapes are made and installed to achieve sealing.

To obtain reliable shut-in performance, four seals must be sound:

(1) Seal between ram front seal and tubing. The ram front is fitted with front rubber. Under piston thrust, the front rubber grips the pipe and seals. If the front rubber is badly worn or torn, high-pressure well fluid will wash through here and cause sealing failure. For blind rams, the front rubbers seal against each other.

(2) Seal between ram top and body. Top rubber is installed on the upper plane of the ram. Under high wellhead pressure, the top rubber presses tightly against the body shoulder, preventing well fluid from leaking through the top bore.

Ram sealing is completed in two stages. First, under hydraulic oil pressure, the ram shaft pushes the ram front rubber to deform and seal the front, while the top rubber and body form an interference-compression seal at the top, creating an initial seal. Second, when pressure exists in the well, fluid in the wellbore pushes the ram front seal from the rear and further squeezes and deforms it. At the same time, fluid from below pushes the ram upward against the upper sealing surface of the body, forming a reliable seal. This is called well-pressure-assisted sealing, including both front ram assistance and top ram assistance, as shown in Figure 10.

Figure 10. Well-pressure-assisted sealing principle

Well-pressure-assisted sealing principle

Obviously, the higher the well-fluid pressure, the better the seal between ram top and body. When well-fluid pressure is very low, the top seal is not fully reliable and may leak. Therefore, during field pressure testing of a Ram BOP, a low-pressure test is often required to check contact between ram top and body shoulder. At 2 MPa well pressure, there should be basically no leakage at the ram top.

Well-fluid pressure also acts behind the ram and pushes the ram toward the wellbore center, making the front rubber grip the pipe in the well. After the rams close, the higher the wellhead pressure, the stronger the well-pressure-assisted sealing on the ram front and the tighter the front rubber seals around the pipe. Because of this assisted sealing, the hydraulic oil pressure in the closing chamber does not need to be very high.

(3) Seal between side door and body. A sealing ring is installed on the mating surface between side door and body. Side-door fastening bolts compress the sealing ring so that well fluid cannot leak from this area. This sealing ring does not wear, but it ages and deteriorates during long-term use and should be replaced regularly according to its specified service life.

(4) Seal between side-door cavity and piston rod. A sealing ring is installed in the annular space between the side-door cavity and the piston rod to prevent high-pressure oil, gas, water or kill fluid in the wellbore from cross-leaking into the hydraulic oil. If high-pressure well fluids break through the rubber sealing ring, they enter the cylinder and hydraulic control lines, contaminate the hydraulic oil and damage hydraulic control valves. During BOP operation, the piston rod reciprocates and the sealing ring inevitably wears. Over time, this can cause seal failure, so damaged seals should be replaced frequently. BOPs above 35 MPa generally have a secondary sealing device at this location.

3) Opening and closing principle of rams

When high-pressure oil from the hydraulic control system enters the closing chambers of the left and right cylinders, it pushes the pistons and drives the ram shafts and left and right ram assemblies toward the wellhead center, closing the well. When high-pressure oil enters the opening chambers of the left and right cylinders, it pushes the pistons and drives the ram shafts and ram assemblies away from the wellhead center, opening the wellhead. Ram opening and closing are controlled by the reversing valve of the hydraulic control system. Opening or closing is usually completed within 3 to 5 seconds.

During closing, hydraulic oil in the opening chamber flows back to the control unit tank through oil passages and hydraulic control lines.

During opening, hydraulic oil in the closing chamber flows back to the control unit tank through oil passages and hydraulic control lines.

4) Shut-in and opening operating steps for Ram BOP

(1) When using a Ram BOP to shut in the well, follow this sequence:

1. Hydraulic shut-in. Operate the reversing valve on the hydraulic control console to close the rams.

2. Manual locking. Rotate the two operating-rod handwheels clockwise so that the locking shafts extend fully and lock the rams. After the handwheels are forced to stop, rotate both handwheels counterclockwise 1/8 to 1/4 turn. The key points are: turn clockwise, reach the stop, then turn back.

3. Bleed hydraulic control pressure. Operate the reversing valve on the accumulator unit to the neutral position, cutting off the hydraulic source and unloading high line pressure.

(2) Opening steps for a Ram BOP:

1. Manual unlocking. Rotate the two operating-rod handwheels counterclockwise so the locking shafts retract fully. After the handwheels are forced to stop, rotate both handwheels clockwise 1/8 to 1/4 turn. The key points are: turn counterclockwise, reach the stop, then turn back.

2. Hydraulic opening. Operate the reversing valve on the hydraulic control console to open the rams.

3. Bleed hydraulic control pressure. Operate the reversing valve on the accumulator unit to the neutral position.

(3) Manual shut-in steps:

1. Operate the reversing valve controlling the Ram BOP to the close position.

2. Manual shut-in. Rotate the two operating-rod handwheels clockwise to push the rams toward the wellbore center. After the handwheels are forced to stop, rotate both handwheels counterclockwise 1/8 to 1/4 turn. The purpose of turning back is to leave proper clearance between locking shaft and piston thread for the next manual operation.

3. Operate the reversing valve controlling the Ram BOP to the neutral position.

The key points of manual shut-in are: turn clockwise, reach the stop, then turn back.

Manual shut-in is essentially the same as manual locking. However, before manual shut-in, the reversing valve on the hydraulic control console that controls the Ram BOP must first be placed in the close position. This allows hydraulic oil in the opening chamber to pass directly to the oil tank. Manual shut-in can be achieved only when the reversing valve is in the close position. After manual shut-in, the reversing valve handle should be moved to neutral before repairing the hydraulic control device.

If hydraulic control fails and manual shut-in is performed, the BOP must still be opened hydraulically when opening is required. Otherwise the Ram BOP cannot be opened. The structure of the manual mechanical locking device allows only manual closing, not manual opening.

5) Use and maintenance of Ram BOP

(1) Preparation before operation. After the Ram BOP is installed on the wellhead and before operation, check the following items. Operate only after confirming that there is no problem.

1. Check whether oil-line connections are consistent with the open and close markings on the BOP. Operate once from the control console at 2 to 3 MPa control pressure. If ram action is not consistent with the control-console handle indication, interchange the lines until it is consistent.

2. Check whether the manual mechanism is in the unlocked position and whether all flowback lines have been installed.

3. Check whether all connection bolts are tightened.

4. Perform a full pressure test to check installation quality. The pressure-test standard should reach the BOP working pressure. After pressure testing, tighten all connection bolts again to correct uneven tightness.

5. Check whether the manual rod operates the rams flexibly and record the number of handwheel turns required for shut-in. After the test, turn the handwheel left to retract and open the rams hydraulically.

6. Check whether the installed ram size matches the downhole pipe-string size.

(2) Use and precautions:

1. A dedicated person should be responsible for BOP use. The operator should understand the working principle, equipment performance and process flow, and be able to operate, maintain, service and troubleshoot the equipment.

2. When there is no pipe string in the well and closing rams for test, maximum hydraulic control pressure must not exceed 3 MPa. When there is pipe string in the well, do not close blind rams.

3. Rams should be fully opened or fully closed.

4. At least one spare set of rams should be kept at the well site so that damaged installed rams can be replaced in time.

5. When closing rams with the handwheel, note that right rotation closes. The manual mechanism can only close the rams and cannot open them. Hydraulic operation is the only method for opening rams. To open rams locked by the manual mechanism, first rotate the handwheel left to the stop, then turn back 1/8 to 1/4 turn to prevent jamming at the unlocked position due to temperature change, and then open the rams hydraulically. When using the manual mechanism to close the rams, the control handle on the console must be in the close position and a sign should be placed on the console indicating the locked state.

6. Open and close the rams once every day to check flexibility.

7. Do not use BOP opening and closing to relieve pressure, to avoid damaging the rubber packer.

8. Keep hydraulic oil clean.

9. After BOP use, the rams should be in the open position.

(3) Disassembly and installation:

1. During wellhead installation, do not install the upper and lower sides of the BOP upside down.

2. Steel rings and grooves should be clean, undamaged, free of dirt and corrosion, and coated with light oil.

3. Connection bolts should be tightened uniformly and diagonally.

4. After installation, perform a hydrostatic pressure test. Test pressure should reach the working pressure and hold for 5 minutes.

The BOP is generally positioned with its two wings parallel to the front of the derrick.

(4) Maintenance. During use, operate the rams once each shift and check the hydraulic control part. If conditions allow, perform a pressure test once each week, overhaul once each year, and after each well, carry out complete cleaning and inspection. Replace damaged parts promptly and apply grease fully to required parts. Apply molybdenum disulfide grease to the top, bottom and side movement surfaces of the ram chamber and rams; apply thread oil to connection-bolt threads.

6) Common faults and remedies of hydraulic Ram BOP

Common faults and remedies are shown in Table 3.

Table 3. Common faults and remedies

7) Basic forms of hydraulic Ram BOP

(1) Hydraulic single Ram BOP. Its structure is shown in Figure 11.

Figure 11. Hydraulic single Ram BOP

Hydraulic single Ram BOP

(2) Hydraulic double Ram BOP. Its structure is shown in Figure 12.

Figure 12. Hydraulic double Ram BOP

Hydraulic double Ram BOP

(3) Hydraulic triple Ram BOP. Its structure is shown in Figure 13.

Figure 13. Hydraulic triple Ram BOP

Hydraulic triple Ram BOP

2. Manual Ram BOP

Manual Ram BOP is a special BOP for conventional downhole operations. Its pressure class is generally 14 MPa or 21 MPa, and some manual Ram BOPs are rated 35 MPa. According to ram quantity, manual Ram BOPs are divided into manual single Ram BOP and manual double Ram BOP.

1) Manual single Ram BOP

(1) Structure and classification. The basic manual single Ram BOP consists of body, ram assembly, side door, manual-control assembly and sealing device, as shown in Figure 14.

Figure 14. Manual single Ram BOP

Manual single Ram BOP

Pressure-containing parts of a manual single Ram BOP, such as body, side door and ram, are alloy-steel forgings. The ram chamber uses an oval structure, improving body stress distribution and body safety performance. The side door is flat-plate type, making ram replacement convenient. The seal between side door and ram shaft combines Y-ring and O-ring sealing, providing reliable sealing and convenient replacement. Ram sealing is split type and consists of top seal and front seal, making disassembly and replacement convenient.

According to ram form, manual single Ram BOPs are divided into blind single-ram manual BOP and pipe single-ram manual BOP. According to connection type, they are divided into double-flange manual single Ram BOP, as shown in Figure 15, and single-flange manual single Ram BOP, as shown in Figure 16. According to performance, they are divided into multi-function manual single Ram BOP and conventional manual single Ram BOP.

Figure 15. Double-flange manual single Ram BOP

Double-flange manual single Ram BOP

Figure 16. Single-flange manual single Ram BOP

Single-flange manual single Ram BOP

(2) Working principle. The manual single Ram BOP works by using the screw in the manual-control assembly to drive the ram to grip the pipe string and achieve sealing. The manual control device is both the transmission mechanism for ram opening and closing and the self-locking mechanism that seals around the pipe outside diameter. The ram assembly uses a one-way sealing ram.

The multi-function manual single Ram BOP is a combination of a self-sealing wellhead preventer and a manual single Ram BOP, as shown in Figure 17. A self-sealing head, or self-sealing rubber element, is installed on the upper flange and fixed by four set screws. During running and pulling operations, the self-sealing head grips the tubing under rubber restoring force and wellbore pressure, sealing the tubing-casing annulus, preventing overflow and kick, and scraping oil contamination from the tubing outer wall into the wellbore. If well pressure is high and the self-sealing head cannot seal normally, or blowout signs appear, quickly close the manual rams so that pipe rams grip the pipe string in the well and seal the tubing-casing annulus before carrying out other operations. In open-hole condition with no pipe, to prevent kick, a blind sealing rod is dropped into the BOP and the pipe rams are closed around the rod to seal the whole wellbore. If well pressure is too high and directly dropping the rod is difficult, the blind sealing rod can be connected to the lower end of the tubing and lowered into the BOP by the hook.

Figure 17. Multi-function manual single Ram BOP

Multi-function manual single Ram BOP

(3) Basic technical parameters. For example, FZ18-21 manual Ram BOP has these basic parameters:

1. Nominal diameter: 180 mm.

2. Maximum working pressure: 21 MPa.

3. Maximum ram stroke: 105 mm.

4. Maximum handwheel torque: less than 412 N.m.

5. Ram specifications: 60.3 mm, 73 mm and blind.

6. Applicable pipe strings: 60.3 mm and 73 mm drill pipe; 50.3 mm and 62 mm tubing.

7. Applicable media: drilling mud, clean water, crude oil and natural gas.

(4) Installation and commissioning of single Ram BOP:

1. Before installation on the well, perform sealing pressure test to maximum working pressure. Use only after passing. When connecting to the wellhead, all connection parts and surfaces should be clean and greased, and bolts should be tightened diagonally.

2. Ram size must match the pipe-string size. If blind and pipe single Ram BOPs are both used, signs should identify them to avoid closing the wrong BOP.

3. Ensure that the workover rig traveling system, rotary table and wellhead are in one vertical line. Fix the BOP and keep it concentric with the wellhead. When the BOP is used alone, a protection flange should be added above it to prevent collision or snagging.

4. After the BOP is connected to the inlet, perform pressure testing to check sealing of all connection parts.

5. Operate the manual control device to close and open the rams. Check flexibility; use only when opening and closing are free of sticking and easy to operate.

6. If a manual-control assembly is used for remote control, install a support bracket at a suitable position.

(5) Precautions:

1. During overflow or blowout, a manual single Ram BOP can seal a pipe string of the same size as the rams. When there is pipe string in the well, do not close blind rams.

2. Before running or pulling pipe, check that the ram assembly is fully open. Keep operation smooth and avoid collision or snagging with the BOP.

3. Never relieve wellhead pressure by opening the rams. After each opening, check that the rams are fully open and not stopped in the middle, to prevent pipe or downhole tools from damaging the rams. If resistance occurs during opening or closing, open the small side cover and clean mud and sand inside before use.

4. Replace the ram assembly or ram rubber only when there is no pressure in the BOP cavity. The ram assembly should be fully open before opening the side door.

5. During use, regularly check whether opening and closing are flexible. If sticking occurs, identify the cause and handle it. Do not force opening or closing, to avoid damaging parts.

6. Keep the BOP clean, especially exposed screw parts, and clean them at any time to prevent mud and sand from jamming the screw and causing inflexible operation.

7. After each well, clean and inspect the BOP. Focus on moving parts and sealing parts, replace damaged or failed parts, and thoroughly clean the BOP exterior, body cavity, ram chamber, ram assembly and screw. After cleaning and drying, apply grease to bolt holes, steel-ring grooves, top sealing shoulder of the ram chamber, bottom support ribs and side-door hinges.

8. Count, clean and box small parts and special tools that have been removed.

9. After maintenance, place the BOP flat in working position on wooden sleepers, avoiding sun and rain. Ambient temperature is -30 to 40 C.

10. Before each pipe-running or pipe-pulling operation, check whether the rams are open. Forced running or pulling is strictly prohibited if the rams are not fully open.

11. Before pressure testing, squeeze injection and similar operations, close and verify the rams. Squeeze injection is strictly prohibited unless the rams are fully closed, to prevent washout of ram rubber and personal injury.

(6) Disassembly and assembly procedure. The disassembly and assembly procedure for a manual single Ram BOP is shown in Table 4.

Table 4. Manual single Ram BOP disassembly and assembly procedure

Opening notes

Open the side door.

Check the O-ring. Note: when opening the side door, the ram core must be fully open.

Remove the ram core.

Check the ram assembly, BOP cavity and all connecting parts. Note: when removing the ram, close the ram core a short distance toward the closing direction and then move it left and right before removing the ram core.

Open the small side cover.

Note: do not lose the fixing screws.

Remove the screw.

Note: first remove the anti-backout locking screw, then rotate the screw clockwise to remove it. Check the screw after removal.

Remove the large side cover.

Remove the protective sleeve, remove the locating snap ring and inspect it.

Remove the sealing parts.

First remove the snap ring, then remove the sealing ring, pressure ring, bearing, screw shaft and seal chamber.

Note: when removing the screw ram shaft, use soft material for tapping to avoid damaging parts.

2) Manual double Ram BOP

A manual double Ram BOP is a combination of manual single Ram BOPs. The body has upper and lower ram cavities. Different ram combinations can be arranged as needed to meet operation requirements, while reducing the height of the BOP stack and facilitating downhole operations. There are two common ram combinations: pipe ram plus blind ram, with pipe ram above and blind ram below, suitable for conventional downhole operations; and pipe ram plus pipe ram, with two different pipe-ram sizes, suitable for operations using two different downhole pipe-string sizes in one job. The structure is shown in Figure 18.

Figure 18. Manual double Ram BOP

Manual double Ram BOP

1. Lock cap; 2. shield; 3. side-door bolt; 4. body; 5. pipe ram assembly; 6. blind ram assembly; 7. side door; 8. ram shaft; 9. screw

In use and daily maintenance, requirements for a manual double Ram BOP are basically the same as those for a manual single Ram BOP.

4. Rotating BOP

The Rotating BOP is installed at the upper end of the wellhead BOP stack, replacing the flow tube. It can seal the annular space formed by casing and tubing string, small drill pipe and similar work strings, and under limited wellhead pressure it allows the operating string to rotate, enabling live-well operations.

The following uses the FSI2-5 Rotating BOP as an example to describe technical specifications, structure, working principle and operation.

1. Technical specifications of FSI2-5 Rotating BOP

(1) Rated pressure: 5 MPa.

(2) Rated speed: 80 r/min.

(3) Maximum internal bore: 120 mm.

(4) Maximum outside diameter: 430 mm.

(5) Height: 950 mm.

(6) Weight: 360 kg.

(7) Applicable pipe strings: 60.3 mm and 73 mm small drill pipe; 50.5 mm and 62 mm tubing; 64 mm and 76 mm kelly.

(8) Applicable media: workover fluid, crude oil, clean water and similar media.

2. Structure and working principle of FSI2-5 Rotating BOP

The FSI2-5 Rotating BOP mainly consists of shell and rotating assembly. The rotating assembly consists of self-sealing head, sealing rubber element, chevron sealing ring, pressure bearing and related parts, as shown in Figure 19.

Figure 19. FSI2-5 Rotating BOP

FSI2-5 Rotating BOP

The Rotating BOP relies on the contraction and expansion characteristics of its sealing rubber element to seal the annular space between work string and casing. Well pressure assists the sealing effect. The pressure bearing carries the load of the pipe string in the well and ensures flexible rotation.

3. Installation of FSI2-5 Rotating BOP

(1) The Rotating BOP is generally installed at the top of the well-control system. If an anti-lift device is required, install manual safety slips above the Rotating BOP.

(2) Before installation, clean the bottom flange, steel-ring groove, bolts and related parts. If the Rotating BOP is used alone, connect it to the wellhead through a matching tee.

(3) During installation, apply grease to steel rings and other connection parts, and tighten bolts diagonally.

(4) After installation, perform a 5 MPa sealing pressure test on the wellhead and hold for 5 minutes. No washout or leakage is acceptable.

4. Operation of Rotating BOP

(1) Running pipe string:

1. If the tool diameter is small, less than 110 mm, directly insert the pipe string and tool. Use the pressurizing device or pipe-string weight to pass the string and tool through the self-sealing head into the well.

2. If the tool diameter is large, more than 110 mm, the self-sealing action of the rotating assembly self-sealing head prevents the tool from passing directly. Remove the clamp of the Rotating BOP, lift the rotating assembly from the shell, connect a guide cone to the lower part of the pipe string, lower it so the guide cone and pipe string pass through the rotating assembly, lift the rotating assembly together with the pipe string, remove the guide cone, connect the tool, then lower the pipe string and rotating assembly into the shell together. Install the clamp and lower the pipe string with the pressurizing device. When the pipe string can overcome the upward force and fall freely under its own weight, the pressurizing device may be removed.

(2) Rotating operation. After the pipe string reaches the planned depth, rotating operation can begin. If rotating operation lasts more than 24 hours, connect cooling-water circulation and confirm normal circulation before continuing.

(3) Pulling pipe string. Pulling is the same as normal operation. When the upward force from well pressure is slightly less than pipe-string weight, the pressurizing device should be installed before pulling. If the tool outside diameter is less than 110 mm, the pipe string can be pulled out directly. If the tool outside diameter is large, remove the clamp and lift the downhole tool and rotating assembly together, then remove the downhole tool. During live-well operation, pull the downhole tool above the blind rams, close the blind Ram BOP first, then open the pressure-relief plug on the Rotating BOP shell. After pressure is confirmed at zero, pull out the downhole tool.

(4) Replacing the rubber element. Remove the clamp, lift the rotating assembly from the shell and place it on a support, remove the rubber-element fixing screws, take out the rubber element and replace it with the required size. Assemble in reverse order. If the rubber element is replaced during live-well operation, first close the pipe rams, install the pressurizing device if necessary, open the pressure-relief plug, bleed pressure, and then replace the rubber element.

5. Precautions for Rotating BOP

(1) Before use, check whether the pressure-relief plug is tightened.

(2) During installation, ensure that derrick center, rotary-table center and Rotating BOP center are in one straight line to prevent collision and snagging during running and pulling.

(3) Tighten and fully install all connection bolts to prevent accidents during operation.

(4) When lifting or lowering the rotating assembly, keep it centered and do not move too fast to avoid damaging the rubber element and sealing rings.

(5) Pay attention to safety when replacing the rubber element and prevent the element or rotating assembly from overturning and injuring personnel.

(6) When wellhead pressure exceeds 5 MPa, do not use the Rotating BOP as a pipe single Ram BOP, to avoid washing out its seals.

(7) During rotating operation, if the bearing area or V-seal area becomes very hot, stop and inspect, then repair or replace related parts in time.

6. Maintenance of Rotating BOP

(1) Wearing parts include seals and rubber element. Each time the rotating assembly is removed, check O-rings and replace damaged ones in time. Check V-rings at the same time.

(2) After 7 cumulative working days, add lithium-based grease to the bearings.

(3) During running and pulling, add lubricant such as soapy water between pipe string and center pipe of the Rotating BOP.

(4) In addition to checking and replacing wearing parts at any time, perform a complete inspection and repair after each well is completed.

7. Disassembly steps for Rotating BOP

During repair, disassemble the Rotating BOP according to the following steps. Assembly is in reverse order.

5. Hydraulically Operated Annular Rotating BOP

The FSI2-5 Rotating BOP is a self-sealing-head type Rotating BOP. Its self-sealing rubber element has poor self-compensation, installing milling and drilling tools is troublesome, and pressure capacity is low. A new type of Rotating BOP has therefore appeared, with larger bore, allowing milling and drilling heads to pass directly through the packing element. The element grips the pipe string, is hydraulically controlled, and seals rotating pipe string under high pressure. It consists of outer upper and lower bodies, piston, inner upper and lower bodies, load bearing, radial bearing, spherical packing element and related parts. The FHS18-35 Rotating BOP shown in Figure 20 has a bore of 180 mm, static sealing pressure of 35 MPa, dynamic sealing pressure of 21 MPa, and rotation speed not lower than 120 r/min. It is mainly used for live-well overhaul or underbalanced overhaul of oil and water wells.

Figure 20. FHS18-35 hydraulically operated Annular Rotating BOP

FHS18-35 hydraulically operated Annular Rotating BOP

6. Wireline BOP

The shell cavity of a Wireline BOP can be divided by structure into circular ram and oval ram types. The oval ram structure has low height, light weight and good sealing performance.

The SFZ12-21 Wireline BOP, Figure 21, uses flange connection and is used for perforating operations.

The FZ7.6-14 Wireline BOP, Figure 22, has three connection forms: clamp, union and thread. It is used for testing and for sealing sucker rods, wireline and small-diameter tubing.

Figure 21. SFZ12-21 Wireline BOP

SFZ12-21 Wireline BOP

Figure 22. FZ7.6-14 Wireline BOP

FZ7.6-14 Wireline BOP

The FH6.5-14X hydraulically operated cylindrical packing element annular Wireline BOP, Figure 23, is used to seal wireline, small-diameter tubing and sucker rods.

Figure 23. FH6.5-14X hydraulically operated cylindrical packing element annular Wireline BOP

FH6.5-14X hydraulically operated cylindrical packing element annular Wireline BOP

7. Shear Ram BOP

During operations on important high-pressure oil, water or gas wells, if tubing is plugged and control is lost, or if no plug has been installed, the casing-tubing annulus may already be closed by the Ram BOP, but large amounts of high-pressure oil, gas or water can still flow out through the tubing. If installing a tubing valve fails and personnel can no longer approach the wellhead, only a BOP equipped with shear rams and capable of full closure can stop the blowout. The shear ram, Figure 24, first shears the tubing or drill pipe in the well and then fully seals the wellhead, preventing accident escalation. After the wellhead is sealed, well killing and tubing fishing measures can be taken.

Figure 24. Shear ram schematic

Shear ram schematic

1. Lower shear ram body; 2. top seal; 3. side seal; 4. cutter-body seal; 5. upper shear ram body

BOP model designation method

BOP model designation method