Well Integrity, from start to finish

April 1, 2015

Weatherford’s Yves Daniel discusses zonal isolation technologies, including an annulus casing packer, made for Australia’s coal seam gas production.

In a conventional CSG well design (left), the practice of cementing individual casing strings with slotted casing in the open hole production zones leads to risks of gas migration and channeling during the cementing operation or microannular gas migration during the life of the well, thus contaminating subsurface aquifers. The recommended design (right) uses enhanced cementing and zonal isolation technologies that lower isolation risks and comply with Australia’s CSG Code of Practice.  Images from Weatherford.

 

Australia has long been a leading oil and gas producer thanks to vast reserves off its western shores. The last two decades have seen further growth in the nation’s production portfolio, thanks to the development of significant coal seam gas (CSG) reserves in Queensland. Recent estimates suggest that Queensland’s CSG reserves could last for more than 100 years at current production levels.

But with this promise of long-reaching gas production comes technical challenges and increased regulatory oversight. Australia’s Coal Seam Gas Code of Practice has established a best practice framework that includes mandatory standards for well construction, monitoring and maintenance, with an emphasis on zonal isolation and protecting the environment. Adherence to these standards requires innovative zonal isolation technologies that work in complicated well geometries and production zones.

Throughout its 50-year working history with Australian oil and gas producers, Weatherford has designed and manufactured zonal isolation technologies aimed at ensuring well integrity while saving rig time and boosting safety and environmental compliance. Inflatable packers have been one area of continued development. By providing immediate and long-lasting seals, these packers ensure reliable zonal isolation for water and gas shutoff, thus preventing gas migration and facilitating two-or three-stage cementing operations. They also serve to isolate the gas bearing coal zones from aquifers that are an essential water source for irrigation and local community water supplies.

The BullDog annulus casing packer (ACP) is an inflatable packer designed to pack off the annular space between the casing and the open or cased hole. Built on standard API tubing or casing sizes and grades, the ACP consists of a reliable locking valve system and rubber inflation elements that can be inflated with either wellbore fluid or cement, as application requirements dictate.

CSG operators have the choice to inflate an ACP with cement due to the reliability that the packer affords during the inflation process. Cement inflation provides longevity of the elastomer seal required to isolate the lower coal seam from subterranean formations and aquifers above. This option also allows the operator to meet Australia’s regulatory isolation requirements that the cement be placed within a few meters across the coal seam face for optimal isolation.

Further isolation assurances are provided when an ACP is used in conjunction with systems that prevent the migration of production fluids between the cement and the casing string. The Weatherford Micro-Seal swellable elastomers, for example, are designed to repair the microannulus gaps that could develop over the life of a well. Such gaps are commonly formed due to prolonged production, temperature fluctuations or movement of the production tubing during a well’s lifetime.

Optimizing packaging and make-ups

The old crating method using single-service wood crates.

 

To be truly effective, the focus on well integrity and optimization must begin before the zonal isolation equipment arrives at the well site. As part of its mandate to conduct operations while reducing impacts to land and decreasing energy usage, Weatherford embarked on a new packaging initiative for its zonal isolation tools in early 2014.

Much of the zonal isolation equipment used in the CSG fields of Australia is supplied from a Weatherford manufacturing plant in mainland China, where it is individually packaged into wooden crates and shipped by boat to a storage facility in Chinchilla, Australia. The wood used in each crate is specially treated to conform to Australian Quarantine regulations. This treated wood is difficult to source, costly to purchase and poses a negative impact to the environment. 

The wooden crates are then transported to the rig site, where each component of zonal isolation equipment—typically an ACP, stage cementing tool and float equipment—is unpacked from their own wooden crate and subsequently made up as a complete assembly.

The life cycle of the wooden crates is short-lived and typically ends at the rig site. The quantity of equipment shipped by this method results in massive quantities of wooden crating waste, adding significant disposal costs and creating a large environmental footprint for every field operation.

Switching to steel

The new initiative was aimed at finding suitable replacement crating material that would not only reduce environmental impacts, but also would streamline shipments and improve efficiency.

Research efforts settled on steel tubulars as the new crating material, which were strong enough to withstand rough handling and storage during shipment, but were cost effective and reusable. The new steel equipment cradles would have to be simple in design and suitable for efficient stacking by forklift or crane at any stage of transport and delivery to the well site.

Further design development led to the recommendation of making up all of the zonal isolation components into one assembled piece at the manufacturing facility in China. This would lower the amount of manual handling and equipment make up by the crew at the rig site, thus lowering safety hazards at the same time.

The final design allowed for three full zonal isolation assemblies per cradle, which translated to one reusable cradle delivering equipment for three CSG wells. Once all zonal isolation assemblies are installed in the wells, the cradles are then mobilized back to the point of origin through a tracking system and inspected and repaired as required. The cycle then begins anew, with the cradles returned to the manufacturing plant for loading of three new zonal isolation assemblies. 

The new method using reusable steel cradles. 

 

Tangible savings secured

This new sustainable shipment option provides several tangible benefits to the CSG operator. Shipping three full assemblies on one cradle streamlines the logistics and procurement processes. It also lowers health and safety risks in the field.

Eliminating wood out of the shipping equation lowers disposal costs for the operator and has the potential to save an estimated 154,000 kgs of treated wood per year (based on an annual field development plan of 700 wells). In total, an operator could save up to $1 million per year on wood crating and in-field equipment make up time alone, with the added benefit of promoting a commitment to safety and the environment.

The first shipment of zonal isolation equipment using the new steel cradling system left China in late 2014, and was successfully delivered to the operator’s rig site in Australia with no damage or issues. This new cradle design, coupled with the proven well integrity benefits that the zonal isolation equipment provides in CSG wells, continues to give Australian operators the piece of mind that comes from partnering with a fully integrated well integrity service provider.



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