Whiting's completion manager details Bakken refrack plans

By Luke Geiver | September 28, 2016

New hydraulic fracturing technologies and techniques deployed in the Bakken are increasing the estimated ultimate recovery rates for both new and previously drilled and completed wells. “So many times in talking to people I hear the comment that they wish they could go back and complete old wells with what we know now,” said Charles Ohlson, completions manager for Whiting Petroleum Corp. “Methods of enhanced oil recovery certainly show promise in the Williston Basin, but for right now,” he added, “we have refracking at our fingertips.”

During the 2016 North Dakota Petroleum Council’s Annual Meeting held in Minot, North Dakota, Ohlson explained Whiting’s history with refracks along with the Denver-based exploration and production company’s current stance on the practice.

2014 Trial and Error

In 2014, Whiting began a refrack campaign on four Williston Basin wells. The wells were located in the operator’s Sanish field acreage and were chosen in large part due to their respective underperformance compared to other wells in the same area. The refrack designs varied from each well, as did the results, Ohlson said. To be generous, he said, only 50 percent of the refrack work was successful.

“We now see that these candidates were chosen for the wrong reasons,” he said, noting that the team learned that choosing a refrack candidate based on poor initial production or because the well had a simple completion methodology by today’s standards, is an inaccurate selection approach. Following the company’s 2014 work on refracks, Ohlson said the strategy of refracking was set aside until this year.

2016 Refrack Approach

As oil prices continued to trade at low prices this year, Whiting’s executive team started looking for more economical projects. “We began to look at refracks again,” Ohlson said. “We knew we operated close to 1,400 wells across the basin and somewhere in there lies several good candidates for enhancing reserves,” he said.

Whiting formed a refrack committee comprised of multidiscinplinary teams comprised of completion engineers, production engineers, well engineers, frack supervisors, service company engineers, landmen and geologists.

The reservoir engineers looked at potential recovery rates, pressures still present in each well candidate and the overall future potential for a well. The completion engineers examined the method that was used to initially frack a well, including the volumes for materials and fluids was used. Production engineers analyzed each candidate for flow assurance issues and if any surrounding wells would need to be shut-in to perform the refracks. The frack supervisors offered an oilfield perspective that helped to ground the selection team’s ideas into the realities of what is possible and plausible on the actual well site. Service companies offered an outside perspective, the landmen engaged Whiting’s partners on the potential refrack wells and the geologist offered a small participation.

After forming the refrack committees, the team began looking at a pool of candidates. The team performed an initial screening that examined well performance, estimated oil in place and any issues that occurred when a respective candidate was drilled or completed. “That was really important to breaking down that list of 1,400 wells,” Ohlson said. After analyzing the well list, the team then analyzed the most promising wells and assigned goals to each related to possible production increases and the optimum refrack jobs that would need to be performed to meet the goals of each well.

Ohlson points to the Twin Shields Butte well as an example of the company’s refrack strategy in action. The well was chosen for a refrack. Surrounded by better forming wells, the team could find no rock quality or pressure reservoir issues with the well. The well was modestly completed, fracked with six stages 700 feet apart on a short lateral.

Through the refrack process, the well will now be completed with new perforations between the existing perforations in a multi-cycle fluids approach that will inject a range of different fluid make-ups into each discrete fracture. “Each cycle will find a new part of the reservoir,” Ohlson said.

After the well has been refracked, the team will then run fiber coil into the well bore and leave it there for a period of time. The fiber coil is equipped with temperature sensors along the entire coil that can tell where new fractures have taken hold and when new oil is flowing through the new fractures. “It will show that we generated new reservies,” he said. “In the long-term, Whiting expects to be doing many more of these.”

Refrack Research

Ohlson’s confidence in Whiting’s 2016 refrack approach is based in part on previous work documented on refracking and on the undeniable production uptick seen in the Bakken using new and enhanced completion methodologies.

According to Ohlson, several studies show that in the Williston Basin, refracks are guaranteed to increase the production of a well an enhance its EURs. Not every well, however, will be economical to refrack.

In the Bakken, roughly 100 wells have been refracked. The practice has been taking place across the country since 2004. Halliburton leads the service providers who perform the services, followed by Liberty Oilfield Services, which formed in 2011 and acquired Sanel Corp.'s U.S. assets in June this year, and then Schlumberger.

Operators also know today that ramping up the number of fracture initiation points and the amount of fluid and sand used to prop open the fractures can greatly enhance the EURs of wells in the Williston Basin.

In 2006, it was common to complete a well with a single frack stage, Ohlson said. Today, most pump 35 to 50 stages on every well. Early style completions were simple because the technology had not yet evolved. “That approach could not create multiple hydraulic fractures along that well bore,” he added. “Later generation wells have involved more intricate methods to really isolate fracture isolation points. Well results have ratcheted up because of that,” he said. “Why not go back and refrack these wells? It will show that we generated new reserves.”