Sustained casing pressure vs. annular zonal isolation packer.
Let us refer to well integrity before tackling sustained casing pressure. Well Integrity is as per NORSOK’s definition, the “application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well.” Long story short, while drilling a well is basically creating communications between geology layers separated by millions of years, we have to prevent formation fluids from migrating out of our knowledge and control.
It has been a standard industry practice to rely on the cement as the primary annular barrier, assuming that the cement placement is satisfactory, with sufficient column height and a good bond. The assumption remains legitimate as long as:
- the wells are shallow.
- the architecture is simple.
- the formations are easy.
New practices bringing new stakes
We are today in a new era. New wells are deeper and deeper, crossing multiple formations with different permeabilities and pore pressures. High pressure and high temperature are increasing the risk of bad cement placement. High pressure and acid stimulations are common practices to unlock the hydrocarbons. However these techniques have a real impact (short or long-term) on the cement’s property.
We are also extending old wells life in mature fields. Producer wells with an initial design for only 10 years of production, might convert into injectors, or might serve for secondary and tertiary recovery. It makes sense to question if the cement has the ability to withstand when changing production and pushing the boundaries.
With no doubt, cementing operations were important before. Now they are becoming the angular stone for deep, extended reach, HPHT, or multilateral wells.
Low-quality cement bond can be catastrophic for safety and the environment and lead to time-consuming and expansive remediation. Casing sustained pressure is a massive concern the industry is now facing. Ageing wells with poor cement lead to small SCP. The casing strength might be sufficient to contain this casing sustained pressure. By the way it still represents a risk of groundwater contamination.
Cement has been an improvement to overcome the challenges to be pumpable. But it is now reaching its limit and needs extra mechanical help. This is where expandable steel packer technology can play a crucial role.
Unwanted and dangerous influxes of formation fluids, solids, and gases.
In deepwater wells, the cement’s ability to reliably contain reservoir pressures is threatened by fluid losses to the formation during cementing operations. Higher pressures and temperatures, longer laterals, and unstable formations have a subsequent impact on these cementing operations.
Deepwater, extended reach, and even multilateral wells mean costly Opex. A low-quality cement bond presents serious safety hazards involving critical risks for the rig crew and the environment.
Mitigating the risk of channeling
Micro-annular channeling and flow, for example, can occur when there is bad-quality cementing across hydrocarbon zones. This micro-annulus flow not only jeopardizes the cement as a primary barrier for well control, but it can also disrupt the operator’s ability to abandon the well in an emergency properly.
In extreme cases, poor-quality cement can allow gas or oil to migrate to the surface and lead to a blowout. Cementing issues are more common than one might want to believe.
Annular zonal isolation packer (AZIP)
The best alternative is to reinforce the cement with a secondary expandable steel barrier above the uppermost hydrocarbon zone. Such a barrier would prevent the unintended and uncontrolled flow of reservoir fluids to the surface – in case of failure of the cement barrier. The annular zonal isolation packer also contributes to boosting the production rates by eliminating the flow.
The system, typically installed as part of the casing string, reduces HSE risks by diminishing issues associated with annular casing pressure and sustained casing pressure. Annular casing pressure builds in or between the tubing and casing strings as the fluid heats up during its production up the well. Saltel Xpandable* expandable steel annulus zonal isolation packer brings an additional safety assurance level. It prevents casing collapse, particularly for numerous wells without bleed-off equipment installed at the wellhead.
Unlike annular casing pressure, sustained casing pressure builds backup in or between the tubing and casing strings after being bled down at the surface, representing an ongoing safety hazard. Sustained casing pressure can cause severe harm or damage to human life, the marine and coastal environment, and property. Thousands of wells in the world have sustained casing pressure in at least one annulus, and serious incidents have been and continue to be the direct consequence of high sustained casing pressure. A smart casing string system, including the pressure compensated expandable steel annular zonal isolation packer, can reduce risks associated with sustained casing pressure for the well’s life.
Sustained casing pressure vs. remedial cement integrity
Numerous wells in North America are going through re-stimulation operations. When sustained casing pressure gives migrations to the casing through corrupted cement, a squeeze cement is necessary.
Unfortunately, squeeze cement operations are temporary solutions and insufficient to withstand the high pressure and high pumping flow rates of proppant. Saltel Xpandable* expandable steel patch can be set over a squeeze to act as a secondary barrier over remedial cement. The patch will be fully supported in such a scenario and will restore almost 100% of the casing integrity. With Saltel Xpandable* expandable steel casing patch, the relined area will fully withstand higher fracturing pressures (up to 15,000 psi internally when supported against a squeeze-cemented casing) and protect the squeeze behind the casing.
As a result, the combination of a patch + squeeze allows
- to retain sustained casing pressure in the annulus
- to initiate or resume fracturing operations