The invasion of pulverized rock formation grains and the resulting"low-permeability crushed zone"is the primary cause of wellbore damage in perforated completions,as established by Behrmann et.al.In order to minimize this damage during the perforating process,it is necessary to provide a dynamic underbalance in the well that will deliberately induce flow into the wellbore for tunnel cleanup.Traditional well fluids have a limited application in depleted reservoirs as the lowest achievable density is on the order of 6.6 ppg.In many depleted reservoirs this density can represent an overbalance.It is not always desirable or operationally practical to provide this underbalance with a gas cushion,and therefore in order to achieve underbalance,it is desirable to engineer a stable fluid with non-damaging chemical properties that would have a significantly lower density.This paper reports on the formulation of super light completion fluids consisting of Shell Sarapar 147 synthetic oil[Shell MDS(M)],3M~(TM)Glass Bubbles as a density reducing agent and an appropriate rheology control agent.Laboratory tests show that density values as low as 5.0 ppg could be achieved.Similar mixtures were prepared and used in perforation operations for Talisman's Malaysia.A total of 72 barrels of lightweight completion fluids at about 5.5 ppg was pumped downhole and the perforation job completed successfully.Production history of the well shows a marked increase in production rate compared to neighboring wells,which produce from the same reservoir,but were perforated traditionally.This technology is not necessarily limited to depleted reservoirs.In normally pressured zones where permeability is extremely low,the fluid provides an opportunity to increase the available underbalance by an order of magnitude to assist cleanup.
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