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Effects Of Reservoir Compaction In Deep Water Environment

Effects Of Reservoir Compaction In Deep Water Environment. N. Yusuf Harold Vance Department of Petroleum Engineering. Texas A&M University. Outline . Objectives Linear Elastic properties of a solid material Elastic properties applied to reservoir rock Review of SPE papers .

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Effects Of Reservoir Compaction In Deep Water Environment

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  1. Effects Of Reservoir Compaction In Deep Water Environment N. Yusuf Harold Vance Department of Petroleum Engineering. Texas A&M University

  2. Outline • Objectives • Linear Elastic properties of a solid material • Elastic properties applied to reservoir rock • Review of SPE papers

  3. Objectives • Understand Reservoir compaction • Determination of parameters affecting dk, df, dh • Review industry works to obtain, dk, df, dh • Develop a criteria / selection tool

  4. Outline • Linear Elastic properties of a solid material

  5. Young’s modulus, E F dz A Z

  6. Poisson Ratio, ν F dz A Z dx X

  7. Bulk modulus, K F F F

  8. Uniaxial modulus, M F Constrained Constrained Constrained

  9. Outline • Elastic properties applied to reservoir rock

  10. Strain relationships for Porous Rock Vb: bulk volume Vp: pore volume Vg: grain volume

  11. Strain relationships for Porous Rock With respect to change in pressure

  12. Rock compressibility Elastic Compressibilities- Definitions Volume changes: Bulk volume: Pore Volume: Pressure changes: Overburden Pressure: Pore Pressure: Bulk Volume Compressibilities Pore Volume Compressibilities

  13. Compressibility relationships for a Porous Rock Zimmerman, 1991 Bulk strain due to pore pressure changes Vs bulk strain due to lab pressure changes Pore strain due to pore pressure changes Vs pore strain due to lab pressure changes BULK STRAIN due to PORE PRESSURE changes related to PORE STRAIN due to CONFINING PRESSURE changes. SIGNIFICANCE: 1 psi change in Confining (or Lab) pressure produce more strain on the bulk & pore volume than 1 psi change in pore pressure by an amount equal to the matrix compressibility. If matrix compressibility is negligible, equal changes in either pore or confining (lab) pressure produce the same bulk and pore volume changes.

  14. Compressibility relationships for a Porous Rock Zimmerman, 1991: OTHER FORMS OF THE RELATION

  15. Compressibility relationships for a Porous Rock Nur & Byerlee, 1971: EFFECTIVE STRESS LAW a is the Biot’s constant SIGNIFICANCE: To simulate an equivalent strain in a porous rock the laboratory stress should be less than the pore pressure depletion by a 1- a.

  16. Uniaxial compressibility Overburden • Loading conditions: • constrained strain • Uniaxial compressibility Cm Constrained Constrained Constrained

  17. d1 d1 s3 l l d d3/2 d d3/2 Typical Lab Testing Uniaxial Strain Test Hydrostatic Test Triaxial Test s1 s1 s1 d1 l d

  18. s1 d1 l d Uni-axial Strain Test / Oedometer Test Simulates the reservoir boundary condition of zero lateral displacement. Provide direct measurement of Cm, uniaxial compaction coefficient. Difficulty: Requires size of core to fit Exactly in the cell. Gap in cells: Lateral strain, disintegration of sample, measurement errors.

  19. d1 s3 l d d3/2 Tri-axial Test s1 Generally used to determine strength under various conditions of stress: i.e. vary s1, s3 Modifications: s3 -> to balance lateral effect of s1 Calculation ofn Difficulty: Requires size of core to fit Exactly in the cell.

  20. d1 l d d3/2 Hydrostatic Test s1 Easiest to conduct, Hydrostatic confining pressure: Measure Pore compressibility : Cpc Bulk compressibility: Cbc Uni-axial compressibility (Cm) can be calculated using: the uni-axial correction factor

  21. Reservoir compaction Constrained Deformation in the reservoir Axial Compaction co-efficient Ca: Overburden Total reduction in reservoir height Constrained Constrained Constrained Neglecting variation of Cm with pressure

  22. Reservoir compaction Factors leading to Reservoir compaction • Large reduction in pore pressure • Large vertical extent of the zone of pressure reduction • Large order of magnitude of Cm • Controlling magnitude of compaction • Pressure maintenance, Limiting Perf interval • Study of Cm

  23. Outline • Review of SPE papers

  24. Paper Review 1 SPE 3730: Land Subsidence Above Compacting Oil and Gas Reservoirs – J Geeertsma • Early work to understand the subject • Causes of compaction / subsidence • Prediction method • Approach: • Observations from field data • Mathematical derivation • Compaction / Subsidence prediction

  25. Paper Review 1 SPE 3730: Land Subsidence Above Compacting Oil and Gas Reservoirs – J Geeertsma • Susceptible reservoirs from observed field Data • Loose / weakly cemented formation • Low depth of reservoir burial (ave: 1000m) • Significant dp (e.g depletion type reservoir) • dp over large interval • Consolidated reservoirs with large dp & H • Factors affecting Cm • Rock type (hard, consolidated, friable, loose) • Degree of cementation • Porosity (high f-> high Cm) • Depth of burial

  26. Paper Review 1 SPE 3730: Land Subsidence Above Compacting Oil and Gas Reservoirs – J Geeertsma • Prediction tool: Calculation of Cm • Sandstone: • 3 rock types, 2 depths • Input variables: • Rock type • Porosity / Stress level • Depth • Interpretation: • Low Cm: 1-3 X 10-5 • High Cm: > 10 X 10-5

  27. Paper Review 1 SPE 3730: Land Subsidence Above Compacting Oil and Gas Reservoirs – J Geeertsma • Limestone: • 2 rock types, 1 depth • Prediction tool: • Limited variables

  28. Paper Review 2 SPE 66479: Compaction Effects on Porosity and Permeability in Deepwater Gulf of Mexico-R.M. Ostermeier • Peculiarity in Deep water Environment • High developmental cost • Typical sand is unconsolidated • Limited Aquifer support • Problematic pressure maintenance • Approach: • Core samples collection over 4 yrs • Laboratory measurement of stress Vs k, f • Development of permeability model

  29. Paper Review 2 SPE 66479: Compaction Effects on Porosity and Permeability in Deepwater Gulf of Mexico-R.M. Ostermeier • Results: Varying responses with 2 extreme cases • Case A: • Geologically younger :softer sands • Exhibiting higher PV compressibility (25) • Compr increases to a max value (120) • Case D: • Geologically older sands: harder • Exhibiting lower initial PV Compr (12) • Slight decrease(10)

  30. Paper Review 2 SPE 66479: Compaction Effects on Porosity and Permeability in Deepwater Gulf of Mexico-R.M. Ostermeier • Porosity & Permeability variations: Case A • Loading Conditions: • Step increases of pressure to 7,000 psi • Time period of 1,500 days • Results: • Porosity: 0.32 – 0.24 (25%), • Permeability: 1.3 – 0.2 D (84.6%)

  31. Paper Review 2 SPE 66479: Compaction Effects on Porosity and Permeability in Deepwater Gulf of Mexico-R.M. Ostermeier • Porosity & Permeability variations: Case D • Loading Conditions: • Step increases of pressure to 8,000 psi • Time period of 300 days • Results: • Porosity: 0.265 - 0.250 (5.7%), • Permeability: 0.65 - 0.475 D (26.9%)

  32. Paper Review 2 SPE 66479: Compaction Effects on Porosity and Permeability in Deepwater Gulf of Mexico-R.M. Ostermeier • Permeability model • Limitations • High error range: +/- 30% • Requires Stress Vs f as input

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