The Armada field development will bring onto production three gas condensate discoveries in Quadrants 16 and 22 of the Central Area of the United Kingdom (UK), North Sea. The largest field, Fleming, will be developed concurrently with the other two deeper reservoirs, Drake and Hawkins. Over one trillion cubic feet of recoverable gas are present. Peak platform production rates of 450 MMscf/d will initially be obtained from eight wells.

The degree of underbalance has a significant impact on well performance and perforation geometry. This paper presents an experimental study to evaluate the effect of underbalance on perforation performance in the Fleming gas-condensate reservoir.

Fleming analogue rock cores were perforated with single shaped charge perforators, and flow tested under simulated downhole conditions. Nitrogen gas was used as the pore fluid for all tests. A brief description of the test facility is included. Cores were taken from outcrop rock chosen to match, as closely as reasonably possible, selected properties of the Fleming reservoir sandstone; in particular, unconfined compressive strength, porosity, permeability, grain size distribution, sorting and shape.

The perforated cores were examined in detail using flow performance comparison, rock mechanical tests, probe permeameter tests, microscopic examination and x-ray scans.

The testing and analysis has enabled:

  • A comparison of the effectiveness of underbalances ranging from 200 psi to 2,000 psi based on flow performance using nitrogen gas as the pore fluid.

  • A comparison of the effectiveness of underbalances ranging from 200 psi to 2,000 psi based on measured perforation geometry. Therefore, a realistic measure of the in-situ perforation geometry.

  • An analysis of the structure and permeability of the crushed zone around the perforations created when perforating at different underbalances with nitrogen gas in the target rock pores.

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