Composite Material Used in Composite Bridge plug and Frac Plug

The definition of a composite is something that is made up of more than one material. For our purposes, composite refers to fiberglass. All composite plugs are primarily made up of fiberglass material, which is a combination of glass fibers and a resin material. The glass fibers are very thin, 2-10 times smaller than a human hair, and are either continuous and wound/woven into the resin or chopped and molded into the resin. The resin material is what binds the glass together, enabling it to take shape. Fundamentally, glass fibers and resin are combined then cured into a solid. From there, the solid is machined into a shape that can be used. There are several ways to combine the resin and the glass to achieve the desired goal. Some of the composite manufacturing techniques used in the construction of composite plugs are filament wound, convolute wrap, and resin transfer composites. Each of these type combine the resin and glass in ways to achieve different properties.

Filament Wound

With filament wound composite, continuous glass fibers are pulled through a liquid resin to coat them. The fibers are then wound around a metal mandrel to create a tube of composite. Once the desired outside diameter (OD) of composite is achieved, the composite tube & metal mandrel are removed from the winding machine and cured within an oven to create a solid composite. After curing, the metal mandrel is removed and the remaining composite tube can be machined into different components.

Filament wound composite is very good for tubular components. They can be highly engineered with specific glass types, resin types, and the wind pattern of the glass fibers. These variables can be altered to achieve different goals including higher collapse, higher tensile, higher temperature rating, easier milling, etc. All of this benefits the production of composite frac plugs because we’re operating within a tube and have to set within a tube (casing).

Also, the filament winding machines can wind up to 30’ tubes of composite, some of which can wind 6 of these tubes at a time. It is easy to produce volumes of filament wound composite with low amounts of labor. This lends itself to producing volumes of product at a lower cost.

Convolute

While filament wound machines use long continuous glass fibers to wrap resin soaked glass into tubes, convolute composite is made using a woven glass fabric that is already impregnated with resin. This “pre-preg” cloth is wound around a mandrel to create a tube, and is then cured to harden into the composite. The benefit of using a fabric made of glass, rather than continuous strands, is that you get the strength of glass in two directions. This adds additional strength to the composite for tensile and compressive applications.

Resin Transfer

With transfer molding the glass fabric is stacked or formed within a mold into a specific shape. The fabric is then impregnated with the resin through a transfer process. The resin is held at a specific temperature in a vessel and the glass fabric is held within a vacuum. The resin is then released into the vacuum environment of the glass, forcing the resin into the voids between the glass fibers within the fabric. The composite is then cured and machined to create the final part.

Molded Composite

Molded composites utilize Bulk Moulding Compounds (BMC) to form composite shapes using either injection or compression molding. BMC is either glass fabric or chopped fibers that are mixed with a resin. These compounds are either placed or injected into a mold and then thermoset or cured under temperature and pressure. The benefit of molded composite is the ability to quickly generate complex shapes in volumes.

There are many ways of combining the resin with the glass and these are just a few of the techniques used in the production of composite frac plugs. What is important is the composite is easily millable into small pieces. Also, the combination of glass and resin results in a specific gravity of 1.8-1.9 creating pieces that are easily lifted from the well during the milling process.

Slip Material

When setting a composite plug the tool is anchored in the well with sets of “slips”. Fundamentally, there is a cone paired with a wedge. The wedge will have sharp hardened areas that when forced up the cone will “bite” into the casing, creating an anchor capable of locking the plug in place and withstanding forces in excess of 200,000 lbs. For the slip to “bite” into the casing the hardened areas or material must be harder than the casing itself, which is typically ~30 HRC.

Composite Body Slips with Inserts

The second most widely used configuration of a slip is a composite body with hardened buttons to provide the anchoring. 

Metallic Buttons

Some plugs have buttons made of metal, either fully cast iron or powdered metals. Powder metal buttons are made from sintering metallic powder into the shape needed from the button. While powder metal sounds like it would be easier to grind/mill up it all depends on the metal powder, heat treatment, and manufacturing process. 

Ceramic Buttons

Some composite plugs utilize a composite slip with ceramic buttons to provide the bite into the casing. While ceramic material is very hard, it is also very brittle. This allows the ceramic buttons to break up better during milling when compared to a metallic button. Ceramic has an SG between 5-6, making them slightly easier to remove during milling that their metal counterparts.

Slip Millability

So much focus is placed on the milling times for a composite plug that the actual goal of milling the plugs can sometimes be forgotten. The ultimate goal of the mill up operation is to remove the plugs from the well. Yes, it's important to get it done quickly and for the pieces to be small. However if you tear through the plug quickly and even get small cuttings, but you don't remove the debris from the well the goal hasn't been achieved. Choosing a plug with metallic slips or buttons will make it harder to remove all of the debris from the plugs just due to the specific gravity of the material.

Vigor's Composite Bridge Plug and Frac Plug are crafted from advanced composite materials, with options for both cast iron and composite designs tailored to customer specifications. Our products have been successfully deployed in oilfields across China and worldwide, receiving outstanding feedback from users. Committed to quality and customization, we ensure that our solutions meet the unique demands of each project. If you’re interested in Vigor's bridge plug series or downhole drilling tools, please don’t hesitate to reach out for more information.

For more information, you can write to our mailbox info@vigorpetroleum.com & marketing@vigordrilling.com