Patent ID: 8726995
Filing Date: 2014-05-20
Classification: E21B

Abstract:
1. A method for perforating a wellbore adjacent to an underground hydrocarbon bearing formation by using reactive shaped charges, the wellbore and formation being such that a maximum pressure gradient achievable between the formation and the wellbore, with minimum achievable hydrostatic pressure in the wellbore, is insufficient to create a cleaning surge flow when using conventional charges for creating perforated tunnels, the method including creating a dynamic underbalance around a charge carrier as a result of detonation of the reactive shaped charges, the dynamic underbalance of sufficient magnitude to create a cleaning surge flow, the method comprising the steps of: a) providing a charge carrier having a substantially empty internal volume and comprising a plurality of cavities for receiving charges; b) filling selective cavities of the charge carrier with charges comprising the reactive shaped charges having a liner component, the number of cavities filled being fewer than the total number of cavities, the number of filled cavities selected on enhancing the dynamic underbalance upon detonation to cause the cleaning surge flow of explosion debris from the formation to the charge holder; c) sealing the cavities of the charge carrier to maintain pressure inside the charge carrier; d) positioning the selectively filled and sealed charge carrier within the wellbore adjacent to said formation, wherein said wellbore has a first pressure substantially equal to a minimum hydrostatic pressure achievable in the wellbore and said formation has a second pressure, and wherein the pressure gradient is the difference between the first and second pressures, and the pressure gradient is of insufficient magnitude to clear the perforated tunnel by the cleaning surge flow if conventional charges were detonated to form the perforated tunnel; e) detonating the reactive shaped charge of the charge carrier to create the perforated tunnel in the formation such that an explosive exothermic reaction takes place between materials comprising the liner component of the reactive shaped charge, and creating the dynamic underbalance; f) creating the cleaning surge flow between the formation and the internal volume of the carrier under influence of the dynamic underbalance; and g) substantially clearing the perforated tunnel in the formation, the perforated tunnel substantially free of a crush zone which would otherwise be formed if conventional charges were used; whereby, the method of detonating the reactive shaped charges has the effect of reducing shot density while providing a greater number of substantially cleared perforated tunnels as compared to detonating conventional charges.