Evaluation of perforation strategies of gas wells in the gulf of Thailand

Abstract

Underbalance perforation has long been recognized as one of the best techniques for mitigating perforating damage. However, the flow efficiency of the perforated wells is controlled by several parameters such as underbalance condition, perforation gun size, shot density, phase angle, and charge type. In this study, seventy pressure transients of seventy gas reservoirs from different wells in the Gulf of Thailand have been analyzed. These reservoirs have different porosities and were perforated with various perforation gun assemblies under different pressure conditions. After analyzing results obtained from seventy gas reservoirs, it can be concluded that the underbalance pressure condition directly affects the perforation damage or skin of perforated gas reservoir, as well as corrected flow efficiency. The higher the underbalance pressure the lower the perforation skin is. As a result, the higher flow efficiency and recovery of gas reservoir can be achieved. However, the underbalance pressure has more impact on the corrected flow efficiency of tight gas reservoirs which has porosity equal to or lower than 18%. The correlations of underbalance pressure required to achieve zero perforaion skin for any reservoir porosity or permeability were obtained and compared to published corelations. From comparison, reservoirs located in different fields require different underbalance pressure condition to achieve zero perforation skin. Regardless of reservoirs properties, depending on perforation charge type, 1500 to 1777 psi underbalance pressure is required to achieve zero perforation skin. There are two recommended charge types for better perforation performance when available or achievable underbalance pressure is lower than 1300 psi.