Blow Out Preventor (BOP) is a very important part of well control equipment and the first thing which we would like to discuss in this article is the BOP stack organization. The BOP stack can be configured in various configurations which must be suitable for the operation.
API has the recommended component codes for BOP as listed below:
A = Annular Preventer
G = Rotating Head
R = single ram type preventer with one set of rams, blind or pipe.
Rd = double ram type preventer with two sets of rams, blind or pipe.
Rt = triple ram type preventer with three sets of rams, blind or pipe.
CH = high remotely operated connector attaching well head or preventers
CL = low pressure remotely operated connector attaching; the marine riser to the BOP
S = spool with side outlet for choke and kill lines
M = 1000 psi
How can I know the BOP configuration and rating from the codes?
When you see the code, you need to read upwards from the bottom of BOP stack. Let’s take a look at the following example:
15M 13-5/8” – RSRRA
This BOP stacks has pressure rating of 15,000 psi with a bore size of 13-5/8” inch. There are following BOP component from bottom to top
Rams – Spool – Rams – Rams – Annular ( see the figure below)
You need to keep in mind that the BOP stack is able to shut the well in and allow you to perform well control operations with the greatest flexibility. Considerations of how to arrange the BOP stack are as follows:
• The BOP stack must be suitable for the drilling operation.
• The stack should be able to serve the stripping operation not just only shut the well in.
• Pressure rating must be higher than expected surface pressure on surface when the well control situation is happened.
• Excessive BOP rams cause difficulty to handle and maintenance. Additionally, the cost of BOP stack is more expensive.
• Sour gas and temperature on surface directly affects the element in the BOP’s/
• The best BOP stack arrangement is the one that is suite for the operation within safety limit.
Reference book: 
Well Control Books
To the contrary of the BOP and the ram placement described above. Always the blind rams are placed at the lowest position in the stack. For reason as if any of the upper rams need replacement or service then the blind rams can be shut and thus leaving the well shut in while performing any service that might be required to the stack. FOR SURE
Tim,
You can put at the bottom as well. However, you don’t have the option to shear and hang off in emergency case such as storm evacuation.
So the drawing above would be from top down. (Rotating Head) Not always used but in situations that the flow might over flow the drill or bell nipple attached to the top of the (Annular). That would be next. The double set of rams would be if two size drilling strings are used or if the sub is to low for the blind ram single on the bottom of the stack shown, Then the bottom double would be the blind ram,The spool for diverting any need be gas. And then the blind on the bottom. Shoot gotta go out to rig. If im wrong could someone reply.
Tim
In the drawing, there is not a rotating head. This illustration demonstrates how the stack arrangement is. The actual BOP depends of the size of the pipe. Nowadays, people tend to use VBR for the pipe rams application because it can cover wide range of the pipe at once.