Theoretical evaluation of replacing residue gas with nitrogen for pressure maintenance in the Wembley halfway B reservoir

Abstract

A study into replacing plant residue gas (methane) with cryogenic nitrogen for the purpose of pressure maintenance in the Wembley Halfway B gas cap is presented. The study considers both reservoir simulation of pool processes to determine the recovery of marketable products and the economic modelling of the processes using the Amoco Canada in-house program GOFER. An investigation of equipment requirements is also considered. The study indicates that lower recoveries of all marketable products will result if nitrogen is used to replace methane. Moreover, the economic benefit of early residue gas sales only marginally compensates for lower liquid recoveries. Residue gas cycling at a 75% voidage replacement ratio, injecting 38 MMSCFD of residue gas, had total liquid (ethane plus) recovery of 83%. When an equivalent volume of nitrogen was injected, the recovery dropped to 69%. A similar recovery was realized at nitrogen injection at a 75% voidage replacement ratio.