Results in Engineering (Sep 2021)
SERA: An ISIP analysis approach to estimate fracture height and correlate stress escalation and relaxation in multifrac horizontal wells
Abstract
In hydraulic fracturing of horizontal wells in unconventional reservoirs, every fracturing stage by increasing the minimum horizontal stress modifies the vertical stress contrast as well as reduces the stress anisotropy. The induced stress gradually declines thereafter due to fracture closure caused by fluid leak-off. The time-dependent stress behavior with localized spatial effects generated by fixed but dynamic sources offers an incentive to fracturing optimization studies. Here, drawing upon the stress superposition principle, an analytical model is derived for Stress Escalation and Relaxation Analysis (SERA) to correlate the stress state at the wellbore. The SERA's model possesses a set of tuning parameters that are adaptively adjusted based on perforation design, waiting time between stage treatments, and ISIP of all completion stages. As a computationally efficient ISIP analysis technique, SERA estimates the average height of wet fracture and sets an upper limit to the critical stress state. In case of a dominant vertical stress contrast, SERA allows to determine explicitly the conditions under which the onset of wet fractures into the bounding layers of lower stress takes place, and when the stress re-orientation controls the fracturing regime, it narrows down the range of estimates of the horizontal stress anisotropy. Furthermore, it provides a tool to design optimal timing and sequencing strategies for alternating fracturing by correlating post-treatment stress relaxation parameters. We validate the model with numerical simulations and perform a sensitivity analysis on the influential parameters that can be carefully designed to give more control over stress shadowing.
