Tuesday, February 7, 2017

Basics of a blowout preventer or BOP

Okay, I know that internet reaches the whole planet, and a diversity of people from elementary to PHDs from Angola to Singapore and Mexico; so, let us for a minute be kind to the younger generation, and put a summary of basic info related to BOPs. One of my favorite petroleum glossaries has been for years the SLB, very accurate and comprised. So let's start with the definition and types of BOPs. Your comments will be very welcome!

According to the SLB glossary, a BOP is:

A large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the BOP and retain pressure control of the formation. BOPs come in a variety of styles, sizes and pressure ratings. Some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drill pipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drill pipe. Since BOPs are critically important to the safety of the crew, the rig and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.

Types of drilling BOPs as follows:

  • Annular or spherical (anular o tipo Hydril), pressures from 500 PSI, 1K, 3K, 5K and 10K PSI:

A large valve used to control wellbore fluids. In this type of valve, the sealing element resembles a large rubber doughnut that is mechanically squeezed inward to seal on either pipe (drill collar, drill pipe, casing, or tubing) or the open hole. The ability to seal on a variety of pipe sizes is one advantage the annular blowout preventer has over the ram blowout preventer. Most blowout preventer (BOP) stacks contain at least one annular BOP at the top of the BOP stack, and one or more ram-type preventers below. While not considered as reliable in sealing over the open hole as around tubulars, the elastomeric sealing doughnut is required by API specifications to seal adequately over the open hole as part of its certification process.

  • Ram BOP (de arietes), singles or doubles. Pressures from 3L, 5K, 10K, 15K and soon up to 20K PSI

A device that can be used to quickly seal the top of the well in the event of a well control event (kick). A ram blowout preventer (BOP) consists of two halves of a cover for the well that are split down the middle. Large-diameter hydraulic cylinders, normally retracted, force the two halves of the cover together in the middle to seal the wellbore. These covers are constructed of steel for strength and fitted with elastomer components on the sealing surfaces. The halves of the covers, formally called ram blocks, are available in a variety of configurations. In some designs, they are flat at the mating surfaces to enable them to seal over an open wellbore. Other designs have a circular cutout in the middle that corresponds to the diameter of the pipe in the hole to seal the well when pipe is in the hole. These pipe rams effectively seal a limited range of pipe diameters. Variable-bore rams are designed to seal a wider range of pipe diameters, albeit at a sacrifice of other design criteria, notably element life and hang-off weight. Still other ram blocks are fitted with a tool steel-cutting surface to enable the ram BOPs to completely shear through drillpipe, hang the drillstring off on the ram blocks themselves and seal the wellbore. Obviously, such an action limits future options and is employed only as a last resort to regain pressure control of the wellbore. The various ram blocks can be changed in the ram preventers, enabling the well team to optimize BOP configuration for the particular hole section or operation in progress.

  • Inside BOP
A valve in the drillstring that may be used to prevent the well from flowing uncontrollably up the drillstring.

  • A set of BOPs or BOP stack:

A set of two or more BOPs used to ensure pressure control of a well. A typical stack might consist of one to six ram-type preventers and, optionally, one or two annular-type preventers. A typical stack configuration has the ram preventers on the bottom and the annular preventers at the top. The configuration of the stack preventers is optimized to provide maximum pressure integrity, safety and flexibility in the event of a well control incident. For example, in a multiple ram configuration, one set of rams might be fitted to close on 5-in. diameter drillpipe, another set configured for 4 1/2-in. drillpipe, a third fitted with blind rams to close on the openhole and a fourth fitted with a shear ram that can cut and hang-off the drillpipe as a last resort. It is common to have an annular preventer or two on the top of the stack since annulars can be closed over a wide range of tubular sizes and the openhole, but are typically not rated for pressures as high as ram preventers. The BOP stack also includes various spools, adapters and piping outlets to permit the circulation of wellbore fluids under pressure in the event of a well control incident.

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