SPE Reservoir Evaluation & Engineering
Volume 13, Number 4, August 2010, pp. 720-729

SPE-139528-PA

CO2 EOR Potential in Naturally-Fractured Haft Kel Field, Iran

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DOI  More information 10.2118/139528-PA http://dx.doi.org/10.2118/139528-PA

Citation

  • Alavian, S.A. and Whitson, C.H. 2010. CO2 EOR Potential in Naturally-Fractured Haft Kel Field, Iran. SPE Res Eval & Eng  13 (4): 720-729. SPE-139528-PA. doi: 10.2118/139528-PA.

Discipline Categories

  • 6.4.2 Gas-Injection Methods
  • 6.8 Fundamental Research in Reservoir Description and Dynamics

Keywords

  • CO2 injection in Fractured reservoir, Fractured reservoir, CO2 injection

Summary

We present results studying the enhanced-oil-recovery (EOR) potential for carbon dioxide (CO2) injection in the naturally fractured Haft Kel field, Iran, on the basis of detailed compositional simulations of a homogeneous single matrix block surrounded by fractures. Oil recoveries from CO2 injection in this idealized model approach 90% for reservoir pressures of 1,400 psia and higher (i.e., at and above current reservoir pressure of 1,500-1,800 psia). It is expected that heterogeneity will reduce recovery on the field scale. This compares with 15-25% recoveries reported for gas-cap expansion and/or injection of hydrocarbon (HC) gas.

Fundamentally different recovery mechanisms develop above and below 2,000 psia, the pressure at which CO2 density equals the reservoir-oil density. At lower pressures, CO2 is less dense than reservoir oil and traditional gas/oil gravity segregation results, with a highly efficient process driven by gravity, compositional effects, and interfacial-tension (IFT) gradients that cause capillary-induced oil flow. At pressures greater than 2,000 psia, CO2 density is greater than reservoir-oil density, resulting in an unusual gravity-drainage mechanism whereby CO2 enters the bottom of a matrix block and pushes oil out the sides and top of the matrix block.

The effect of several key parameters has been studied in detail--matrix permeability, matrix-block size, matrix/matrix capillary continuity (stacked blocks), and the use of mixtures of CO2 and HC gas. One of the key results is how the rate of recovery differs for combined injection of HC gas and CO2, and how it varies for CO2 injection for different model parameters.

EOR results are affected by grid sensitivity. Grid effects have been quantified and compared for different model parameters. Final EOR assessment is made using models where sufficient grid refinement is used to minimize grid sensitivity.

© 2010. Society of Petroleum Engineers

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History

  • Original manuscript received: 25 August 2009
  • Meeting paper published: 22 November 2009
  • Revised manuscript received: 9 April 2010
  • Manuscript approved: 20 April 2010
  • Published online: 19 August 2010
  • Version of record: 24 August 2010