The In Situ Situ Stress Field of the West Tuna Area, Stress Field of the West Tuna Area, Gippsland Gippsland Basin: Basin: The In Implications for Natural Fracture- -Enhanced Permeability Enhanced Permeability Implications for Natural Fracture and Wellbore Wellbore Stability Stability and Emma J. Nelson, Richard R. Hillis, Scott D. Mildren, Jeremy J. Meyer
Gippsland Location Map Gippsland Location Map
Objectives Objectives The Problem: The Problem: The R- - and S and S- -reservoirs have low permeability. reservoirs have low permeability. The R Drilling has been associated with stuck pipe and fluid loss Drilling has been associated with stuck pipe and fluid loss Aims: Aims: • • Determine the in situ stress tensor Determine the in situ stress tensor • Determine the extent and nature of natural fracturing • Determine the extent and nature of natural fracturing • Probability of fracture enhanced permeability • Probability of fracture enhanced permeability • Finite element modelling to assess wellbore wellbore stability stability • Finite element modelling to assess
Presentation Outline Presentation Outline • • In Situ Stress in West Tuna In Situ Stress in West Tuna • Fracture characterisation and fracture enhanced permeability • Fracture characterisation and fracture enhanced permeability • Wellbore stability and finite element modelling of near stability and finite element modelling of near wellbore wellbore stress stress • Wellbore • Conclusions • Conclusions
Reservoir Stresses Reservoir Stresses S v • • S Hmax S Hmax Orientation Orientation • S V Magnitude • S V Magnitude S Hmax • S hmin Magnitude • S hmin Magnitude • S Hmax Magnitude • S Hmax Magnitude S hmin
S v Magnitude S v Magnitude Pressure (MPa) 0 10 20 30 40 50 60 70 80 90 100 0 500 ρ av ρ from checkshot av from checkshot velocity velocity 1000 Depth (m) 1500 2000 ⌠ 0 ρ (z)g = ρ Sv = (z)g dz dz Sv ⌡ 2500 z 3000 3500
S hmin Magnitude S hmin Magnitude Pressure (MPa) 70 80 0 10 20 30 40 50 60 0 Leak Off Tests Leak Off Tests 500 LOP 1000 Pressure P c 1500 Depth (m) 2000 Time 2500 3000 3500 4000
Stress at the Wellbore Wellbore Wall Wall Stress at the Stress at the Wellbore Wall Compression σ H σ H Tension Kirsch Equations σ θθ = (σ Hmax + σ hmin ) – 2 (σ Hmax - σ hmin ) cos2 θ - ∆ P
S Hmax Orientation S Hmax Orientation S Hmax Orientation Breakout Circumferential Stress (MPa) Compressive rock strength DITF Tensile rock strength Azimuth with Respect to Maximum Horizontal Stress
S Hmax Orientation S Hmax Orientation S Hmax Orientation Breakout DITF Breakout DITF 0 180 360 0 180 360 1 metre 1 metre West Tuna 8 138º º N N 138
S Hmax Magnitude S Hmax Magnitude S S Hmax Hmax Ori Ori = 138° N = 138° N S S v = 21 MPa = 21 MPa v P P P = 9.8 MPa = 9.8 MPa P S S hmin = 21 MPa = 21 MPa hmin S Hmax = 38 MPa S = 38 MPa Hmax Depth = 1000 m Depth = 1000 m S Hmax > S hmin ~S v
Presentation Outline Presentation Outline • • In Situ Stress in West Tuna In Situ Stress in West Tuna • Fracture characterisation and fracture enhanced permeability • Fracture characterisation and fracture enhanced permeability • Wellbore stability and finite element modelling of near stability and finite element modelling of near wellbore wellbore stress stress • Wellbore • Conclusions • Conclusions
Natural Fractures Natural Fractures Natural Fractures Electrically conductive fractures in cemented sandstones
Fracture Susceptibility Fracture Susceptibility Fracture Susceptibility Conductive fractures Conductive fractures Mohr Circle Mohr Circle Shear Stress (MPa) Normal Stress (MPa) • • Conductive fractures are optimally oriented to be hydraulically conductive in the far Conductive fractures are optimally oriented to be hydraulically conductive in the far- -field field • Conductive fractures are restricted to cemented sandstones with low matrix permeability low matrix permeability • Conductive fractures are restricted to cemented sandstones with • Conductive fractures may be important to reservoir connectivity • Conductive fractures may be important to reservoir connectivity
Presentation Outline Presentation Outline • • In Situ Stress in West Tuna In Situ Stress in West Tuna • Fracture characterisation and fracture enhanced permeability • Fracture characterisation and fracture enhanced permeability • Wellbore stability and finite element modelling of near stability and finite element modelling of near wellbore wellbore stress stress • Wellbore • Conclusions • Conclusions
3D Homogenous Block Model Results 3D Homogenous Block Model Results 3D Homogenous Block Model Results Circumferential Stress (MPa) Verification using Kirsch equations σ θθ = (σ Hmax + σ hmin ) – 2 (σ Hmax - σ hmin ) cos2 θ - ∆ P σ θθ σ H - σ σ h σ = 3 σ max = 3 H - h - - P P w w - - P P o o = 100 MPa θθ max σ θθ σ h - σ σ H σ = 3 σ - P P w - P P o min = 3 h - H - w - = 20 MPa θθ min o Azimuth with Respect to Maximum Horizontal Stress
3D Layered Model 3D Layered Model 3D Layered Model SANDSTONE Circumferential Stress (MPa) 133 MPa Compressive strength Material Properties 21.1 MPa Azimuth with Respect to Maximum Horizontal Stress ‘Sandstone’ E= 40 GPa SHALE υ =0.25 Circumferential Stress (MPa) ‘Shale’ E = 8.5 GPa υ =0.35 Compressive strength ‘Sandstone’ 40.7 MPa 17.1 MPa Azimuth with Respect to Maximum Horizontal Stress Circumferential Stress
Conclusions Conclusions Conclusions 1. The in 1. The in situ situ stress field in West Tuna is on the boundary of strike stress field in West Tuna is on the boundary of strike- - 1. The in situ stress field in West Tuna is on the boundary of strike- slip and compression. slip and compression. slip and compression. 2. 2. Fractures are optimally oriented to be hydraulically conductive in Fractures are optimally oriented to be hydraulically conductive in 2. Fractures are optimally oriented to be hydraulically conductive in the far- -field. field. the far the far-field. 3. Breakouts and DITFs DITFs only occur in cemented sandstones. This only occur in cemented sandstones. This 3. Breakouts and 3. Breakouts and DITFs only occur in cemented sandstones. This can be explained by stress partitioning. can be explained by stress partitioning. can be explained by stress partitioning.
Acknowledgements Acknowledgements Acknowledgements Glen Nash Glen Nash Thanks to: Thanks to: Thanks to: Mike Power Mike Power Wayne Mudge Mudge Wayne Adem Djakic Adem Djakic Andrew Marr Andrew Marr
Recommend
More recommend
