The Secrets of Slickwater

An industry staple reveals the merits, challenges of slickwater fracks. For the wells that match up with the selection criteria for a slickwater treatment, the production results are undeniable.
By Luke Geiver | July 14, 2014

Mike Stemp is familiar with the tug-of-war nature of unconventional oil production. After 20-plus years spent in the oil industry working in locations around the world, he knows that completing a well requires the right balance of production efficiency, proven science and economics. Today, Stemp is the corporate engineering advisor for fracturing at Sanjel Corp., the Calgary-based oil services firm that entered North Dakota in 1998. Sanjel’s Williston Basin operations now include five fracturing fleets consisting of over 60 frack pumps, 8 blenders, 4 coiled tubing fleets and other services including cementing. The Williston Basin is one of Sanjel’s largest operations, Stemp says, an operation he describes as experiencing massive growth. Because of that massive growth, his team has become in-tune with the complexities of slickwater fracks.

Although slickwater fracks have become one of the most popular completion methods in the play today, Stemp offers a friendly disclaimer to all current or prospective clients. “I have to remind everyone that slickwater fracks are not a one-size fits all approach. Each geological area may call for a different technique,” he says. But, for the wells that match up with the selection criteria for a slickwater treatment, the production results are undeniable and economics can make sense when Sanjel’s team of fracturing and reservoir experts examine all the data paying particular attention to the quality of the reservoir.

The Meaning of the Name
Traditional hydraulic fracturing techniques are often compared to interconnected channels. A conventional fracture method utilizes a viscous fluid to carry proppant into a horizontal lateral. The fluid-proppant mixture is pumped downhole to wedge the rock open, creating long, wide channels for trapped hydrocarbons to flow through. These bilateral fractures can extend between 500 and 1,000 feet outwards from the wellbore. The fluid mixture is typically pumped into the well at 20 to 40 barrels per minute. The maximum proppant concentrations in the fluid range from 4 to 12 pounds per gallon. The permeability of the rock to be fractured dramatically affects the type of treatment required. The tighter the rock, the more fracture complexity required. Conventional hydraulic fracturing methods typically do not create this complexity.

A slickwater frack offers a peculiar outcome. The technique is simple by design, but it can create a larger, more complex fracture network. The method creates a fracture network that is closely related to a broken pane of safety glass with all the tiny fragments attached. “If you have ever seen a piece of safety glass and it has shattered into a thousand little pieces but they all stay connected,” Stemp says, “that is more or less what we are trying to do with slickwater fracks but in a three dimensional network.”

By simplifying the fluid used to fracture the rock and carry the proppant, slickwater can create a more complex fracture network. The idea, according to Stemp, is to take advantage of the situation below ground. The low permeability rock can be fractured into a complex network of multiple channels when a thinner fluid is pumped at higher than traditional rates. Because the water is non-viscous it does not create a single wedge or frack wing but rather multiple fracks which form a dendritic-like or branching fracture network. “We found that the small stimulated reservoir volume (SRV) created by conventional fracturing was  leaving a lot of the reservoir untreated,” Stemp says. “By lowering the fluid viscosity and changing the proppant type, we can essentially improve production by increasing the total fracture network. We call them slickwater because the fluid used is non-viscous and slick.”

Deploying Slickwater Fracks
Because a slickwater fluid does not include gels or other viscosity enhancers, more fluid is required to move the amount of proppant necessary to effectively prop open the stimulated reservoir. “We pump at a very high rate,” Stemp says. A conventional frack job would be pumped at 20 to 40 barrels per minute. A slickwater job is pumped at 60 barrels of fluid per minute or more. The main additive to the fluid is a friction reducer, an element of the fluid necessary to allow for the high pumping rate. For every gallon of fluid pumped, a completions crew will add from 0.25 to a maximum 2 pounds of proppant.

To effectively pump the fluid mixture at the desired rate, Sanjel's teams typically use 15 to 20 pumping trucks, a large increase from the 5 to 10 trucks used on a well site in the past. Although Sanjel works with operators who complete their wells in various stages or with differing designs, Stemp says most are running three perforation clusters per discrete fracture zone and each well is completed with 25 to 40 zones. For each discrete fracture zone, Sanjel's team will pump slickwater first to initiate the fracture, followed by ramps of low proppant concentration, then a PAD or a sweep stage to create additional fractures, followed by additional stages of 0.25, 0.5, 0.75 and 1.5 pound per gal of proppant.  In some instances that process would be repeated three to four times per zone. In the end, the results are massive. On a per zone basis, a well could use 150,000 pounds of proppant and 250,000 to 300,000 gallons of water. The end result could push the well totals for proppant and water to 4.5 million pounds or greater, and 8 million gallons or greater. “In many cases, the vast quantity of fluid and proppant can make or destroy the economics of the treatment,” he says.

Some operators are using slickwater-based fracks that include a process known as a tail-in. To perform the process, the completion team will use slickwater and a smaller sized proppant combo for the initial stages of the job, followed by larger size proppant and conventional frack fluids towards the end of an individual treatment on a zone. “This is called a hybrid system,” he says. The slickwater mixture is used to create the complex network away from the well bore and then the conventional system to tie all these branches together. The conventional frack fluids used near the end of a slickwater treatment on a single zone creates a wide flow path which connects all the small channels created by the slickwater stages.  
 
For Sanjel and the entire industry, designing a fracture network based on the abilities of slickwater was not as difficult as learning the most efficient way to physically align the elements needed to perform the frack job. “It has been a massive learning curve for the region,” he says. “The logistics for all of the proppant required the trucks to move the fluid and everything else involved was difficult. But now, the industry is comfortable doing this. We are comfortable, and successful in doing this,” he says.

The advent of slickwater frack designs has required Sanjel to increase the number of pumps in the region. The company has also had to work through the logistics aspect of the practice, including water tank storage and supply.
Although the process is proven to increase production, Stemp does say each operator needs to understand the reservoir they have and whether or not the costs of added water, proppant and proppant quality/type will be outweighed by the reservoir’s potential production increase. For many operators, the allure of greater production has tugged them towards slickwater, he says. Sanjel is continuing to develop and apply evolving technologies to keep pace with the industry’s demands for efficiencies and continuous improvements” adds Stemp.

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Author: Luke Geiver
Managing Editor, The Bakken magazine
lgeiver@bbiinternational.com
701-738-4944