Single-Trip Perforation/Stimulation and Testing Method Removes Formation Damage, Reduces Operational Costs, and Increases Estimated Production in the Mato Rico Field in Parana Basin, Brazil
Authors: Etcheverry Carlos Fulvio , Carneiro Sergio , Leite Francisco Oliveira 
Published: December 2007

Abstract
Stimulation combined with perforating during a drill stem testing (DST) operation offers a unique operational technique that shows promise of resolving many inherent formation damage problems that can occur when perforation is conducted during completion activities. This paper will discuss a case history in which a unique perforation-stimulation operation was attempted for the first time in Brazil. The method was suggested to a major operator who wished to test a damaged formation of an exploratory gas well in the Mato Rico Field in Parana Basin, Brazil. The primary requirement of the operation was to obtain the main reservoir parameters (pressure, permeability, skin and extension) of a sand formation in which an earlier openhole drill stem test had already identified severe near-wellbore damage. Since the procedure would not involve the main target of the well, extreme cost efficiency was required.
With the method suggested, a well with an acid fluid column is pressurized with nitrogen to above fracturing pressure of the formation before the gun is fired. Gas is then injected with acid to create short fractures extending from the perforation tunnels. The presence of gas lowers the amount of liquid contact with the formation plus the additives in the acid reduced surface tension. This action facilitates the well’s coming into production after perforation and results in a reduction of formation damage.
The perforating/stimulation method creates highly conductive short fractures that outweigh any restriction that might be caused by the perforating debris. The extreme energy at the moment of perforating along with the rapid expansion of the high-pressure nitrogen gas create high erosion velocities that remove perforation debris from around the wellbore and extend the perforations several feet into the formation. Following the initial perforation, additional pumping of nitrogen extends the created fractures even further into the formation. The debris and the crushed zone that exists when the guns detonate will be pushed away from the wellbore during the pumping stage. This will greatly diminish any adverse effects that overbalanced perforating may cause in productivity.
After careful review of alternative methods, this procedure was chosen. It provided excellent testing results and was successful in removing most of the previously identified skin damage. This was verified by the subsequent testing, which showed that the skin damage had been reduced to 14 from its original 89. This reduction allowed the same quantity of gas to be produced at a lower drawdown.
The positive effects from using the combined technologies include: Savings in rig time.Time and cost of additional stimulation jobs to flow the well had traditional procedures been used.Better understanding of the formation response to stimulation treatments and fluids.A significant increase in the gas production from an originally estimated 10,000 m3 /D to 380,000 m3/D.