On the far end of the flowback spectrum is a completion process called soakback. Instead of allowing the well to flow back right after completion, some operators are forced to shut in their wells for months at a time until takeaway capacity is available. The completion fluids then soak into the shale rock. What happens during that process is still being debated, but flowback analysis may provide some answers.
Robert Hawkes, the corporate director of reservoir solutions at Trican Well Service, has been studying the issue for the past few years and collaborates with the research team at the University of Alberta. He is pushing a controversial theory, which holds that, in many cases, the water used in stimulation treatments is not a damaging mechanism for shale reservoirs. Hawkes said his idea is supported by a number of Canadian operators that have recently come to the same conclusion.
Among the most common fears is that the water swells the clays inside the shale, which then leads to fracture damage. “Yet, in the past 15 years, we’ve been putting a ton of water in these same reservoirs and getting good results,” Hawkes said. He thinks such results have been possible because the mixed fabric of shale can tolerate vast volumes of water.
This mixture of clay and stronger materials might also explain why production sometimes comes on very strong in gas wells where flowback is commenced months after the completion. In one gas well that was shut in for a year after completion, the initial production rate was five times that of a similar offset well brought on just days after completion.
Hawkes said in many other instances, shut-in wells are observed to have very clean wellbores, which indicates that the propped fractures healed around the near-wellbore area instead of being flushed out, which is often the case during normal flowback operations.
“That’s where the eureka moment was for me,” he said. “My approach is if you can keep it shut in and you don’t mind losing the water, that’s to your benefit and it’s not going to be detrimental, which is really unconventional thinking for all of us.”
So while this leads to a stronger initial well performance, what operators are not saying is whether soaking enhances recovery rates. However, soaked wells may be more economically beneficial since they incur less water disposal costs for the first few months of the well’s life.
Of course, a high degree of patience on the part of the operator is required to realize such a benefit. Hawkes said the biggest issue with soaking at the moment is that “it’s almost impossible” for reservoir simulators to account for the physics, which makes it hard to determine where it may apply.
