Coreflood Studies of Tertiary CO2 Flood in Naturally Fractured Midale Formation in Southeast Saskatchewan

摘要

The distinctive geology of Weyburn and Midale reservoirs has important implications for the design of a CO2 injection process for these fields. These are contained within two distinct zones of the Mississippian Carbonate formation; The tight, high-porosity Marly zone sits on the top of the low-porosity Vuggy zone. The latter zone has a higher permeability and is more extensively fractured vertically than the Marly zone. These geological features result in a relatively unswept Marly zone after waterflooding. The Marly/Vuggy sequence presents a opportunity for a CO2 flood to take the advantage of the gravity segregation to recover the large remaining oil target in the Marly zone. How it could be an effective process in the Midale reservoirs needs to be investigated.rnA series of coreflood tests were conducted to simulate the tertiary CO2 injection in Marly/Vuggy zones in the Weyburn and Midale reservoirs. Berea core with different permeabilities were split lengthwise. The halved segments of the core were butted together to represent the Marly and Vuggy zones. Water (in waterflood mode) and CO2, (in tertiary CO2 flood mode) were injected into the bottom high-permeability section of the dual-permeabilityrncore. The coreflood results showed that, in the tertiary CO2 flood, CO2 could migrate to and recover the oil from the top low-permeability zone which was poorly swept by the waterflood. Also, the effects on tertiary oil recovery of operating pressure, injection rate, and permeability contrast were significant.