Completing a producing zone(s) behind straddle packers is a common occurrence; hundreds of wells have been completed in this manner. Should such wells produce trouble-free and meet expectations, there is not much to ponder over; but if not, the options for executing an enhanced stimulation treatment have been limited. Generally, treatment has consisted of pumping and squeezing away the treatment into the perforations via the sliding side door(SSD) and hoping for the best. The preferred technique is to improve the injectivity into the perforations by "spotting" reactive fluids at the perforations or using some type of mechanical action such as "perforation jetting" to break up blockages in the perforation tunnels. This is only possible when perforations are accessible through the wellbore.
These problems become more complicated if the zones of interest are sandstone reservoirs. A study1 in the late-1990s revealed a success ratio in the 30-40% range when treating such formations.
This paper addresses such a scenario in which a dirty sandstone reservoir, not previously matrix-acidized, was producing at sub-par rates (declining to the point of being negligible). The zones were completed between straddle packers and were only accessible through SSD, 100 ft above the perforations.
The prudent decision was to stimulate, but make all efforts to maximize the chances of success. Apart from applying the best practices in sandstone acidizing technology, a true fluidic oscillator (TFO) was included as a stimulation tool. This tool provides a continuous pressure pulse in the fluid system that allows solids buildup within the perforations to fatigue and break up while the acid system works on the rock matrix.
The results from the treatment of this well were exceptional and will be detailed in this paper. The production improvement was 10-fold over its prestimulation performance.