Underbalanced, through-tubing perforating operations represent a compromise between the pressure differential needed for effective perforation cleanup and the differential that causes sand production or tends to the the gun and cable. This paper explores the dynamic variables involved in through-tubing perforating and describes a new model developed to evaluate the underbalance perforating conditions and predict the effects on the wireline gun system. Using this model, formations can be aggressively perforated with the optimum safe underbalance pressure, and completion operations can also be combined with closed chamber test techniques to accurately evaluate the completion efficiency and initial reservoir parameters.

Utilizing new wireline technology to measure downhole pressure and temperature during perforating, operational data were obtained from numerous field tests to validate the dynamic model. The results indicate that the model reliably predicts the maximum underbalance to avoid sanding, the change in gas cushion pressure, the volume of reservoir fluid influx and the gun/cable movement Examples from Louisiana Gulf Coast wells are used to illustrate the application of the design model and the associated closed chamber test technique.

The transient pressure data from the closed chamber test are used to accurately evaluate reservoir parameters and completion efficiency. The data are analyzed by assuming the formation is subjected to an impulse rate created by briefly flowing the well. In addition, by measuring the surface and bottomhole pressure during the perforating operation, the approximate fillup rate can be determined as well as the cumulative volume of fluid entry. In the field examples presented, these data are utilized in other interpretation techniques, such as rate convolved pressure analysis, and the derived formation parameters are compared with conventional well test results.

You can access this article if you purchase or spend a download.