BASIC COMPONENTS OF BOP STACK a) Annular Preventer

The Annular Preventer is designed to close and seal over the open hole or around different shapes such as square and hexagonal kelly, tool joint etc including wire line except stabiliser and bit.

b) Ram Type Preventer

Pipe ram is designed to close and seal around a pre designated size of pipe, whereas, presently available variable rams can seal around a pre designated range of pipe size. Blind ram is used to close and seal an open hole. However, these days blind cum shear rams are in use, which can shear the pipe and seal the open hole as well.

Note : Pipe rams are not designed to close and seal around tool joint and coupling. c) Drilling Spools

Choke and kill lines may be connected either to side outlets of the BOPs or to a Drilling spool installed below at least one Ram BOP. Utilization of the BOP side outlets reduces the number of stack connections and over all BOP stack height. However, a drilling spool is used to provide stack outlets (to localise possible erosion in the less expensive spool) and to allow additional space between preventers to facilitate stripping, hang off, and/or shear operations.

Criteria for Drilling Spools

a) 3M and 5M arrangements should have two side outlets no smaller than a 2-inch nominal diameter and be flanged, studded, or hubbed. 10M, 15M, and 20M arrangements should have two side outlets of minimum 3-inch nominal diameter and should be flanged, studded or hubbed.

b) It shall have a vertical bore diameter equal to that of mating BOPs and at least equal to the maximum bore of the upper most casing/tubing head.

c) It shall have a rated working pressure equal to the rated working pressure of the installed ram BOP. For drilling operations, well head outlets should not be employed for choke and kill lines.

d) Choke Manifold and Choke Lines

The choke manifold consists of high pressure pipe, fittings, flanges, valves and manual and/or hydraulic operated adjustable chokes. This manifold may bleed off well bore pressure at a controlled rate or may stop fluid flow from the well bore completely, as required.

Choke Manifold

a) Manifold equipment subject to well and/or pump pressure (normally upstream of and including the chokes) should have a working pressure equal to or greater than the rated working pressure of the ram BOPs in use.

b) The choke manifold should be placed in a readily accessible location, preferably outside the rig structure.

c) All choke manifold valves should be full bore. Minimum two valves are recommended in choke line immediately after the BOP stack with rated working pressure equal or greater than the rated working pressure of Ram BOP in use. One of these two valves should be remotely controlled. During operations, all valves should be either fully opened or fully closed.

d) A minimum of one remotely operated choke should be installed on 10000 psi and above rated working pressure manifolds. Generally, remote operated choke is not installed in 5000 psi working pressure manifold. If conditions dictate like for example the frequency of use of chokes is high, it will be prudent to use a remote choke (in addition to adjustable choke) in 5000 psi working pressure choke manifold. Choke manifold configurations should allow for re-routing of flow without interrupting flow control.

e) Pressure gauges suitable for operating pressure and drilling fluid service should be installed so that drill pipe and annulus pressures may be accurately monitored and readily observed at the station where well control operations are to be conducted.

f) Rig air systems should be checked to ensure their adequacy to provide the necessary pressure and volume required different controls. The remotely operated choke should be equipped with an emergency back up system such as a manual pump for use in the event air becomes unavailable.

Installation guidelines – choke lines

The choke line and manifold provides a means of applying back pressure on the formation while circulating out influx from the well bore.

The choke line and lines downstream of the choke should:

a) 1. Be as straight as possible. Wherever the bends, blocks and tees are provided, they should be targeted to minimize erosion.

2. For flexible lines, manufacturer’s guidelines should be consulted on working minimum bend radius to ensure proper length determination and safe working configuration. b) Be firmly anchored to prevent excessive whip or vibration.

c) 1. Have a bore of sufficient size to prevent excessive erosion or fluid friction. Minimum recommended size for choke lines as per API is 2” nominal diameter or 3M and 5M arrangements and 3” nominal diameter for 10M and above rated arrangements.

2. Minimum recommended nominal inside diameter for lines downstream of the chokes should be equal to or greater than the nominal connection size of the chokes.

3. For air or gas drilling operations, minimum 4” nominal diameter lines are recommended. 4. The bleed line that bypasses the chokes should be at least equal in diameter to the

choke line.

Kill lines and kill manifold

Kill lines are an integral part of the surface equipment required for well control during drilling. The kill line system provides a means of pumping into the well bore when the normal method of circulating down through the kelly or drill pipe can not be employed. The kill line connects the drilling fluid pumps

to a side outlet on the BOP stack. The location of the kill line connection to the stack depends on the particular configuration of BOPs and spools employed; the connection should be below the ram type BOP most likely to be operated.

Installation guidelines - kill lines

a) All lines, valves, check valves and flow fittings should have a working pressure at least equal to the rated working pressure of the ram BOPs in use.

b) For working pressures of 3000 psi and above, flanged, welded, hubbed or other end connections that are in accordance with API Specification 6A, should be employed.

c) Components should be of sufficient diameter to permit reasonable pumping rates without excessive friction. The minimum recommended size is 2-inch nominal diameter.

d) As per API, two full bore manual valves plus a check valve or two full bore valves (one of which is remotely operated) between the stack outlet and kill line are recommended for installations with rated working pressure of 5000 psi or greater.

e) Lines should be as straight as possible. When bends are required to accommodate either dimensional variations on sequential rig ups or to facilitate hook up to the BOP, the largest bend radius allowable under the hook up restraints should be provided. For flexible lines, manufacturer’s guidelines should be followed to ensure safe working configuration.

f) All lines should be firmly anchored to prevent excessive whip or vibration. g) The kill line should not be used as fill-up line during normal drilling operations.

Standard choke and kill manifold

The standard choke and kill manifolds in use/ available in ONGC are: i) 4 1/16” –5000 psi working pressure.

ii) 4 1/16” –10000 psi working pressure. iii) 3 1/16” –15000 psi working pressure.