This paper presents a case history of a technique utilized in a loose sand fontation to keep constant pressure underbalance during tubing fill-up after TCP shooting.

The method allows a good evaluation of the formation characteristics scon after the TCP shooting, providing an early knowledge of the formation productivity before the final completion with gravel-pack and Electric Submersible Pumps. Moreover, it gives the means for a correct pump design and the evaluation of the gravel pack efficiency.

This technique developed by Agip Recherches Congo was applied to shallow reservoirs consisting of loose sands filled with rather viscous oil. All the wells are completed with gravel packs and electric submersible pumps (ESP).

Prior to shooting the tubing is filled with nitrogen and the pressure is discharged to have desired under-balance. To keep underbalance constant during tubing fill up, WPH is discharged to decrease backpressure.

The fact that a practically constant pressure underbalance occurs during perforation clean up allows a reliable interpretation of the bottom hole pressure transient.

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