Increasing Production by Maximizing Underbalance During Perforation Using Nontraditional Lightweight Completion Fluid

Abstract

Summary The invasion of the pulverized formation rock grains and the resulting low-permeability crushed zone is the primary cause of wellbore damage in perforated completions, as established by Behrmann et al. (1991). 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 because the lowest achievable density is on the order of 6.6 lbm/gal. 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; therefore, to achieve underbalance, it is desirable to engineer a stable fluid with nondamaging chemical properties, which would have a significantly lower density. This paper reports on the formulation of superlight completion fluids consisting of Shell Sarapar 147 synthetic oil (SO) [Shell Middle Distillate Synthesis (MDS), Kuala Lumpur) and 3M Scotchlite hollow-glass spheres (HGSs) (3M, St. Paul, Minnesota, USA), also known as glass bubbles, as a density-reducing agent, with an appropriate stabilizing agent. Laboratory tests show that density values as low as 5.0 lbm/gal could be achieved. Similar mixtures were prepared and used in perforation operations for Talisman Malaysia. A total of 72 bbl of lightweight completion fluids (LWCFs) at approximately 5.5 lbm/gal was pumped downhole, and the perforation job was completed successfully. Production history of the well shows marked increase in production rate compared to the neighboring wells, which produce from the same reservoir but were perforated traditionally with little or no underbalance. 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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