Advances in technology and improved techniques have led to production growth in U.S. shale plays. But the industry can do better in one area that has a long history in North America, according to a fracturing optimization expert.

That’s restimulation, or refracturing. The process has been used on vertical wells dating back to the 1950s but it has gained attention in recent years as operators and oilfield services companies work to get more oil or gas from horizontal wells. Speaking during EnerCom’s 21st Oil and Gas Conference in Denver on Aug. 18, Colorado School of Mines instructor Mike Vincent pointed out that the industry has restimulated more than 250,000 wells over the past 60 years, but could improve on the process. Improving on the process could, ultimately, lead to higher profits for operators and service companies.

“A lot of my clients have pumped the exact same pump schedule 70 times in a row, and they made money on every refrack; but that doesn’t mean that we optimized. That doesn’t mean that we learned,” Vincent said.

Knowledge gained from other campaigns must be incorporated into future designs. “We should learn enough [about] refracturing that it changes the game in how we design new wells, how we space them, how we frack them; and that link is pretty weak inside of a lot of companies.”

His words were delivered as the oil and gas industry continues recovering from a downturn that drove companies toward technology and techniques in the quest to become more efficient.

Successful refrack campaigns can lead to, and have led to, production growth; however, failed refracks provide opportunities to improve the process. . Further optimization could lead to better frack designs, stage and well spacing, greater production and ultimately, more profit.

Failed campaigns have some commonalities, according to Vincent: refracks are pumped without targeting a specific mechanism or a tailored design. On the first refrack attempt, companies will often use the same approach that perceived industry leaders have used; and refrack campaigns are not designed with learning something in mind. Past lessons are not incorporated into future designs, he added, and poor refrack well candidates are sometimes selected. Candidate selection criteria vary by reservoir.

Vincent said he didn’t intend to be critical, but intended to shed light on opportunities that properly designed, pumped and selected refrack jobs bring.

“When refracks work, they are fantastic investments,” he said.

Among the opportunities he listed were:

  • Profit: Compared with drilling a new well, refracks have a lower capital investment and minimal environmental footprint. Carrying out refrack campaigns can also keep employees on the payroll while drilling fewer new wells.
  • Resolve “non-unique” interpretations: This is where learning lessons from refrack campaigns can come into play. There can be multiple unknowns when trying to determine the reason behind a decline curve—poor reservoir quality, limited drainage, and insufficient frack length, he said. Comparing changing oil rates over time after a frack and refrack can provide insight on reservoir potential.
  • Diagnosis: If an operator wants to study how to improve production near the wellbore vs. far-field, a small refrack—using 5% of the original proppant volume— could be pumped to help pinpoint opportunities.
  • Learning from others: Don’t reinvent the wheel, Vincent said. Look at what has and hasn’t worked for others in the reservoir or similar reservoirs. The industry has pumped at least 400 refracks in the Bakken, but he said little has been learned. Better collaboration and advanced planning are needed, he said.

He added that industry’s current mode is in-filling drilling, putting 10 to 40 wells per square mile depending on the play—requiring millions of dollars per square mile in capital to harvest the resources.

“If you can support that much drilling costs, that’s fantastic,” he said. But the frack engineer said he takes this personally.

“It means I’m not doing a very good fracking. I ought to be able to harvest these reserves with 10 wells that are better fracked, or five wells or three wells per square mile if it had good enough fractures that were durable, or the right plan for restimulation,” he added. “That is where I think an operator has the best chance to learn something from refracks.”

Velda Addison can be reached at vaddison@hartenergy.com.