DRILLING & COMPLETION
New P&A technology cuts
operational time in half
Dual-string section mill delivers permanent barrier offshore Australia
Ensuring wellbore integrity remains a critical need long after a well has reached the end of its productive life and economic feasibility. During the plug-and-abandonment (P&A) phase of the well lifecycle, operators must erect a permanent and impermeable barrier within the wellbore and the formation to
prevent the escape of hydrocarbons. Preventing leaks is important
not only from an environmental perspective but also to mitigate the
potential future economic impact on operators, who remain financially
and legally responsible for their abandoned wells.
Operators want to meet the regulatory requirements for P&A
while at the same time limiting total operational expenditures. Other
than removing the liability associated with an unsecured well, P&A
offers little return on investment when compared to the costs incurred. In the past, the industry has seen decision-making that can
have catastrophic consequences later. Not only do leaks create an
environmental hazard, but also relocating abandoned offshore wells
on the seabed and the consequential leak remediation can cost many
millions of dollars. Several recent high-profile leaks from abandoned
wells offshore Australia underscore this point.
Australia has a vast amount of offshore oil and gas wells. This large
number of offshore/deepwater assets means that, as more wells
age, offshore P&A and optimal methods for leak prevention will be
increasingly prominent issues for the region. Furthermore, regulatory requirements dictating the material, length, and depth of cement
plugs—according to specific wellbore parameters—are becoming
more stringent. As a result, service companies are developing new
technologies and techniques to help operators achieve permanent,
compliant, efficient, and cost-effective P&A.
Conventional P&A method
The perf, wash, and squeeze method involves perforating tubulars
at selected depths across production zones and then squeezing cement
slurry into the annulus. Once it hardens, the cement acts as a seal
against pressure from above and below, and prevents the migration
of hydrocarbons from the formation.
In certain applications, this method can be effective in providing a
long-term barrier between the wellbore and formation and mitigating
hydrocarbon leaks. However, it is not always the optimal choice for
offshore/deepwater environments in which the stakes—and penalties—associated with P&A failure are high. It is not always evident
whether a perf, wash, and squeeze job is truly validated and it is possible to leave wells vulnerable to cement channeling when the slurry
fails to uniformly set between the casing and the borehole. When this
happens, micro-annuli can form between the outside diameter (OD) of
the casing and inside diameter (ID) of the wellbore. If there is a poor
cement job, downhole pressure can enable hydrocarbon migration
through the cement and result in leaks at the surface.
Additionally, the perf, wash, and squeeze method may not adhere to
regulator y standards for offshore/deepwater environments because it
does not provide a solid, uninterrupted open-hole plug. With growing
frequency, regulators are calling for the removal of entire sections
of casing to expose the rock face and enable setting cement plugs
across the entire borehole, which results in a rock-to-rock barrier and
cement-formation bond. Indeed, this is occurring across Australia.
Future of P&A
Achieving a rock-to-rock, cement-to-formation bond can drastically reduce the risk of hydrocarbons escaping from the formation
or transmigration into aquifers. A rock-to-rock barrier equates to the
safest, most ef fective way to prevent leaks in abandoned offshore wells.
Once set, cement plugs create a hydraulic seal that conforms to the
After the DSSM’s cutting blades open a window through the 133⁄8-in. casing,
the 17-in. milling blades mill the remainder of the casing to set the stage for
a competent cement to formation bond. (All images courtesy Weatherford)