Near Miscible CO2
Near Miscible Application in Arbuckle Reservoir
- Determine the feasibility of using CO2 displacement at near miscible conditions to improve oil recovery with injection pressure below minimum miscibility pressure.
- Develop appropriate plan for field test if the project shows that significant oil can be recovered by the CO2 process operating at near miscible conditions.
Why Near Miscible?
- Many reservoirs are not considered for CO2 miscible flooding because the maximum reservoir pressure that can be attained is less than the minimum miscibility pressure (MMP).
- Near miscible displacement refers to a process occurring at pressure slightly below MMP and is between immiscible and miscible.
- Within the pressure range near miscible, significant oil recovery was observed in slim-tube experiments and to a lesser extent in the core tests.
- Mechanisms in the displacement include extraction, oil swelling, oil viscosity reduction and favorable relative permeability as a result of reduction of interfacial tension between CO2 and oil.
- Oil Field: Ogallah Unit, Trego County, Kansas
- Operator: Carmen Schmitt, Inc.
- Formation: Arbuckle
- Formation depth: 3950-4060 ft
- Reservoir temperature: ~110 – 125 °F
- Reservoir pressure: ~ 1150 psia
- MMP: 1350- 1650 psig (110 -125 °F)
- Oil API Gravity: 33.34
- Oil characterization
- Density, viscosity measurement
- Swelling/Extraction test
- Slim tube test
- Core flood experiment
- Phase behavior model
- Geological model
- Compositional reservoir model
Structure Top of Ogallah Unit
Incremental Oil Production at Well 3-2
- Properties of Ogallah unit oil produced from an Arbuckle reservoir in Kansas were determined at reservoir temperature from a series of phase behavior and slim-tube experiments where CO2 was dissolved in or used to displace the oil. The MMP at 110 ºF was 1350 psig. The MMP increased to 1650 psig when the temperature increased to 125 ºF.
- At near miscible condition (pressure greater than 1100 psig), the oil viscosity was reduced by a factor of five due to the dissolution of carbon dioxide. Formation: Arbuckle
- Recovery of more than 50% of the waterflood residual oil from Berea, Baker dolomite and Arbuckle reservoir rock was obtained when CO2 was injected at the current average reservoir pressure of 1150 psig, substantially less than the MMP (1350 psig).
- Significant extraction of oil by CO2 started at pressure of 1150 psig which indicated that extraction/vaporization is the primary mechanism for oil recovery in the near miscible region from 1100 psig to 1350 psig at 110 ºF.
- The simulation results indicate that near miscible displacement is achievable in lease 3 (E. A. Scott) at current reservoir operation pressure.
- The incremental oil recovery generally increases with the injection pressure. The oil recovery efficiency was increased by 1.3 to 4.8% as a result of CO2 injection.