by John Callihan
November 11, 2015

Today, 90 percent of natural gas wells drilled in America require fracture stimulation to remain or become viable. The process requires an array of products and technologies to successfully stimulate natural resources from the ground. Blenders are one of the most crucial components in a fracturing site's success.

As the heart of any fracturing job, blenders must offer peak performance at all times in operation, but also be reliable, easy to use and simple to maintain. For instance, one company's tub cleanout ports in the inner ring of the blender tub simplify maintenance while the self-flush and self-cleaning feature eliminates the need for major cleanouts of buildup, resulting in more dedicated uptime.

Blenders pull in water from the frac tanks with a suction pump, which sends the water to a 10 barrel mixing tub. The mixing tub mixes the water with proppant that is delivered to the mixing tub by sand screws (typically three). Additional chemicals can also be delivered to the mixing tub. Dry chemicals are delivered by a dry additive system mounted on the blender. Liquid additives are delivered by a liquid additive system either mounted on-board or off-board the blender. A discharge pump then pulls the mixture from the mixing tub and discharges it to the discharge manifold on the blender. From the discharge manifold, the mixture is sent to the manifold trailer, then transferred to the frac pumps, which discharge the mixture under pressure to the wellhead. Typically there is one primary blender and one backup blender on location, so the dependability of the blender is critical.

Image 2. Many blenders can be trailer-, skid- or chassis-mounted.Image 2. Many blenders can be trailer-, skid- or chassis-mounted.

Because no two wellsites are the same, blender manufacturers need to work closely with end users to provide unique solutions such as the flexibility to create a blender based on the user's preferred controls or the manufacturer's controls. Companies can offer broad-based experience in controls and in-house software development rather than "off-the-shelf" products to integrate systems from different manufacturers and of varying age.

Additionally, some blenders provide increased versatility with a dual-discharge option that allows discharge from either the unit's driver or passenger side. The option offers greater flexibility when it comes to hooking up to the blender. Dual-discharge ports can be especially valuable at well locations with tight access or on challenging terrain.

Image 3. Blender controls cabin Image 3. Blender controls cabin

Continuing the versatility, many blenders can be trailer-, skid- or chassis-mounted as well as available with automatic transmissions. Offering the advantage of shifting from first to second gear based on the rate of the job, the automatic transmission delivers more horsepower compared to hydraulic for greater performance at the wellsite. The two-engine design enables greater flexibility to ramp up rotations per minute (rpms) on low-rate blending jobs. The blender's engineered flow dynamics enable the most efficient pumping of fluids and the most continuous flow.

One company's blender design includes a proprietary positioning of jets that delivers high flow rates and consistent mixing energy, a smooth fluid surface and the ability to effectively mix at most tub levels while minimizing air entrainment for quicker reaction to density changes. Some blenders offer flow rates up to 130 barrels per minute (bbl/min) and as low as 70 bbl/min.

Heavy-duty fluid preparation and proppant-proportioning blenders can execute a fracturing pump design that controls suction and discharge functions along with the addition of proppant in ramp or stage modes. Liquid additives that run on a continuous basis during a treatment are monitored and controlled by a central control panel system on these types of blenders.

Proppant Selection

The development of hydraulic fracturing technology has led to the usage of proppants, which keep the fissures open for the oil and gas to flow towards the wellhead. Proppants must perform in a variety of conditions, including high pressures, temperatures and fluids. That's why selecting the right proppant for the specific downhole conditions of a hydraulic fracture is one of the crucial factors in the success of well completion. Three types of proppants, silica sand, ceramic and resin-coated, come in an array of sizes, shapes, strengths and densities.

Blenders with the central control panel system can improve components' functions and ensure consistent performance regardless of conditions. As an added assurance of continued performance, automatic and manual controls can provide redundancy in a system failure.

Some automatic systems offer various operation modes that give operators constant system performance from on-board screens.

Other features of various blenders include climate-controlled cabins and emergency stop/kill functions that allow the unit's shutdown in extreme situations.

With the diversity of wellsites and the challenges they each pose, it is vital to have a blender that can be customized to the users' unique needs.