For years, an unresolved question for those drilling horizontal wells has been: Does it matter if it is toe-up or toe-down?
Horizontal wells generally follow an up or down slope following the most productive rock with some large changes in elevation from the heel—the curve from vertical to horizontal—to the toe.
Results from modeling did not settle the matter. Recently, Devon Energy offered its response based on the performance of more than 300 similar wells drilled in the Cana-Woodford Shale in Oklahoma.
The comparison was possible because the company had mass-produced similar wells, giving it a large sample of wells to study with 4,800-ft laterals where it fractured 10 stages with 40 perforation clusters using 3.5 million lb of proppant located in a compact area with similar geology in the three depths studied.
The analysis was done in a way that ensured, as much as is statistically possible, that “only toe-up or toe-down could be affecting the production performance of the wells analyzed,” said Sam Browning, a reservoir engineering for Devon who delivered the paper at the 2016 Unconventional Resources Technology Conference.
It concluded that toe-up wells produce more. And the greater the elevation change between the heel and the toe, the greater the impact.
“The more toe-up they are, they [wells] appear to be better, and the more toe-down is worse,” Browning said, adding “All the best wells were toe-up.”
Devon found the toe-down wells produced 25% less based on a year’s worth of production, he said. The difference was narrow in the early days of production and widened over time.
The results were compared based on the depth of the wellbore—shallow, middle, and deep—because of differences in the zones. For example the condensate-rich production in the shallower zone could be less able…