A Conceptual Change in Perforating Dynamics

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A new approach to underbalanced perforating to achieve clean, zero-skin perforations is replacing the prevailing underbalanced concept of perforating job design. One approach is through the use of methodology being employed in the Schlumberger perforating system for clean perforations, Perforating for Ultimate Reservoir Exploitation (PURE). Ongoing research and field application show that the control-manipulation of the pressure transients in wellbore immediately after perforating has a direct impact on perforation cleanup. This technique is being combined with a new deep-penetrating shaped charge, the Schlumberger PowerJet Omega, to create a dynamic underbalance transient, cleaning the perforations and improving well performance. Methodology Application Job design consists of an evaluation of available well data, reservoir data, perforating systems, and methods to convey these systems. Applicable in various environments, the design facilitates pressure transient development in the wellbore immediately after perforating (Fig. 1) and can be effective when initial static well conditions are underbalanced, overbalanced, or balanced. The underbalance effect happens quickly (within milliseconds of the guns firing) and lasts for 100 to 500 milliseconds. It is during this time that zero-skin perforations are created. The job design considers different factors, including flow area into the gun string, charge selection, additional chambers when required, hydrostatic pressure, well fluids, reservoir properties, and completion characteristics. Used in new wells and old wells with existing perforations, the method has proved successful in oil and gas producers, water and gas injectors, depleted wells where pumps are employed, and naturally flowing wells. In Combination Combining PURE with PowerJet Omega (Fig. 2) is designed to enable clean perforations and deeper penetration, bypassing formation damage and cleaning the perforation tunnel, eliminating perforation skin and allowing optimal production. In a recent job, this shaped charge shot at 6 spf provided the same productivity as the former leading deep-penetrating charge at 12 spf in less rig time, with less casing damage, less debris, and ultimately, less chance of problems. The deep-penetrating charge can also be used alone to improve productivity in wells where the PURE technique is not an option, such as in very-low-pressure reservoirs or where there must be gas in the wellbore at the time of perforating. It has been witnessed in the field results that by using a combination design, tight gas wells can be brought on stream without near-wellbore acid-wash treatments. Wells have been perforated successfully in reservoirs with pressures as low as 1,000 psi and permeabilities as low as 0.05 md gas. In addition to wells with significant potential for productivity improvement, candidates include wells requiring expensive operations to establish underbalance, wells that require near-wellbore acid washes after perforating, and those that require high underbalanced pressures for cleanup.