Acid stimulation may be performed in a well to remove damage to the wellbore and to increase its productivity, or inj ectivity, by enhancing the near-well permeability. Damage in a typical well may extend radially several feet, or more, away from the wellbore. As such, in order to permeate the formations surrounding the wellbore, acid may be sprayed at a high pressure. Formation heterogeneity may lead to uneven distribution or conformance of the acid. Optimal acid stimulation may be difficult because of several factors. For example, for oil reservoirs, acid has lower viscosity than oil, resulting in fingering or viscous instabilities. Further, acid tends to flow along the path of least resistance in the higher permeability zones, leaving the lower permeability zones unswept. Also, the downhole acid flow is usually diverted based on stimulation schedules, designed in the pre-job phase, that are not optimized based on the real reservoir heterogeneity. Even if the real reservoir properties are considered in the pre-job phase, the stimulation evaluation is typically done based only on post-stimulation productivity and injectivity increase.
Applying the acid by creating pressure pulses may improve the acid flow into a formation, even in damaged or lower permeability zones. However, determining an optimal pressure in real time for the pressure pulses at each position within the wellbore remains a problem. Further, pressure pulses created by some commercial pulse devices are asymmetric, having a sharp increase and a slow decrease. This may result in insufficient power to enable the acid to permeate the formation efficiently.
USPTO Backgrounds
USPTO Backgrounds