Achieving effective stimulation across zones not readilyaccessible is a common challenge in the oilfield. Severalauthors1-3 have presented case histories in which horizontalwells completed with slotted liner, gravel pack, internal gravelpack, or plain sand screens were difficult to stimulate becausethere was no easy way to effectively remove drilling fluidfilter cake from the wellbore walls. Similar inaccessibility isencountered when dealing with straddled completions, whereout of necessity, the producing zone is placed behind straddlepackers that are extremely challenging to reach. Anotheraccessibility problem is encountered when a “fish” becomescaught up across the perforated interval and accessibility isagain denied.Should such wells produce trouble-free and meetexpectations, there is not much to ponder; but if not, theoptions for executing an enhanced stimulation treatment havebeen limited. Generally, treatment has consisted of pumpingand squeezing away the treatment into the perforations andhoping for the best. The preferred technique is to improve theinjectivity into the perforations by “spotting” reactive fluids atthe perforations or using some type of mechanical action suchas “perforation jetting” to break up blockages in theperforation tunnels. This is only possible when perforations orpays are accessible through the wellbore.These problems become more complicated if the zones ofinterest are sandstone reservoirs. A study4 in the late 1990srevealed a success ratio in the 30–40% range when treatingsuch formations.This paper primarily deals with a case history in which asandstone reservoir, not previously matrix-acidized, wasproducing at sub-par rates, eventually declining to a negligibleproduction status. The zones were completed between straddlepackers and were only accessible through a sliding side door(SSD), 100 ft above the perforations.The prudent decision was to stimulate, but make all effortsto maximize the chances of success. Apart from applying thebest practices in sandstone acidizing technology, a true fluidicoscillator (TFO) was included as a stimulation tool. This toolprovides a continuous pressure pulse in the fluid system thatallows solids buildup within the perforations to fatigue andbreak up while the acid system works on the rock matrix.The results from the treatment of this well wereexceptional and will be detailed in this paper. The productionimprovement was 10-fold over its prestimulation performance.
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