Scott Gordon, Director of RBP product line, The WellBoss Company, describes a century of evolution for well control barriers and the growing role of retrievable bridge plugs in modern well integrity strategies.
As long as we have been drilling for hydrocarbons there has been a need to have the ability to isolate pressure bearing formations from flowing to surface. That requirement remains throughout the lifecycle of all assets today, whether that be during the initial well construction phase, the production phase, or the last act of plug and abandonment.
Well control barriers have evolved considerably over the last 100 years and probably never more significantly than over the last two decades. In the 1920s the first flow control devices were introduced to complement what had been the primary means of hydrostatic barrier or kill weight. These devices were very simple slip lock, type devices that were maybe not the most reliable of barriers.
By the mid 1950s the first profile-based barriers with selective abilities were introduced. These became much more reliable and the status quo for mechanical barriers for many years, and are still used in many completions being constructed today.
By the early 1990s, a new generation of retrievable bridge plugs was emerging: some were purely mechanical, with others now being set with a series of new battery powered electro-mechanical setting tools. Having the ability to generate downhole push/pull forces, eliminating the need for explosives, was a significant step change, enabling a rapid advancement with retrievable bridge plugs.
The challenges with profiles
Profile barriers have been a very reliable means for well isolation, and are comprised of two key components: the lock mandrel complete with equalising device, and the corresponding profile which was installed as an integral component of the completion during construction. The lock mandrel can be maintained to comply with quality standards; however, the corresponding landing profile has been exposed to well flow, intervention activities, etc., since its installation. That then raises doubts about the status of its integrity. Has it corroded over time? Has it been damaged due to thousands of feet of wire and coil being conveyed through it? Can you guarantee its integrity for being a primary well control barrier?
Most landing profiles subsequently introduce wellbore restrictions to the completion design, with it not being uncommon to have at least two or three of these strategically placed within the completion design. This inherently introduces flow impedance – then in the reverse, limiting fluid flow during stimulation operations – which in turn introduces back pressure during pumping and treatment operations. A further downside is the fact that your landing nipples for accepting barriers is restricted to predetermined depths, with little flexibility.
An additional requirement for profile-based barriers is the requirement to mechanically manipulate tools, with the conveyance method, which predominantly has been slickline. This subsequently means that the landing profiles are required to be placed above doglegs or laterals.
Why retrievable bridge plugs?
The premier retrievable bridge plugs (RBPs) available on the market now provide some additional assurances, with industry recognised certification under ISO 14310 and/or API 11D1. For many operators around the world this is not even a point for discussion, with barrier philosophies stipulating these qualifications as minimum requirements for well control barriers. The requirement sees these devices exposed to rigorous test protocols with pressure reversals to the working pressure and within a temperature window. This qualification allows an additional layer of due diligence to the well control barrier, knowing that it has been qualified within an operating envelope that exceeds the application requirements. This obviously eliminates any concerns there may be with the integrity of a landing profile of a legacy type of barrier.
Eliminating the need for restricted landing profiles and moving to a mono-bore completion completely removes the downside of the flow restriction during production and well stimulations operations, with the additional benefit of having unlimited flexibility for barrier placement. This places your primary well control barriers exactly where you need them.
The advancement of powered mechanical setting tools reduced the dependency on manipulating setting sequences, allowing RBPs to be conveyed and installed in horizontal and lateral applications, with either coil tubing or electric line tractors.
RBPs have also become an efficient means of installing shallow set barriers for remedial wellhead work, tree removal, and blow out preventer (BOP) removal or installation, becoming an effective alternative to back pressure valves (BPVs).
Read the full article in the July/August issue of Oilfield Technology Magazine.