Report

Reservoir StressSensitivity BGD Smart JM Somerville M Jin Reservoir Stress-Sensitivity • Reservoir properties and therefore behaviour influenced by changes in stress • Caused by either changes in pore pressure or temperature, or combination • Properties = permeability, dimensions, integrity Stress-Sensitivity Scales • Near wellbore – permeability – (stress skin cf skin caused by invasion) – failure • Increasingly distant from the wellbore – permeability • Whole reservoir – permeability, directional floods • Field – compaction, subsidence, seal alteration Stress-Sensitivity Scales • Near wellbore – Influenced by UBD – permeability – (stress skin, no skin caused by invasion) – failure • Increasingly distant from the wellbore – permeability Reservoir Stress-Sensitivity: a multi-disciplinary challenge More Realistic Reservoir Model Better Decisions Reservoir Stress-Sensitivity: a multi-disciplinary challenge More Realistic Reservoir Model Stress Sensitivity Better Decisions Better Decisions Re:• • • • • • • • • • Reserves Well design PI Well locations Production strategy Reservoir management (inc 4D seismic) Seal integrity Compartmentalisation Facilities Efficacy of UBD technology and methodology All impacting recovery factor and costs HWYH-399 Key: Breakout from CBIL(A) Drilling-induced tension from STAR HWYH-394 Key: Drilling-induced tension cracks Bed boundary Fracture Unclassified, possible stylolite All from STAR The Conceptual Model • The reservoir consists of blocks or layers of intact rock bounded by discontinuities • The reservoir is stressed in an anisotropic manner • The whole system exhibits hysteresis Thinly-bedded interval in the Annot Sandstone.This interval is underlain and overlain by more ‘massive’ sandstones. The Reservoir Discontinuities “Intact” Rock Boundary and Local Stresses within the Reservoir sv Reservoir sh sH sv sv sh Boundary or Regional Stresses sH sv sh Local Stresses sh Intact Rock Properties (stress-sensitive values where appropriate) Ambient porosity and permeability Elastic constants E and v Biot’s coefficient Failure (Fracture) Criteria Vp and Vs velocities Vp anisotropy at ambient conditions Permeability at reservoir stress conditions Palaeomagnetic trial s1 s2 e1 e2 P and S waves Fluid flowing at pressure s2 Stress-Sensitive Values of:• • • • • Elastic Moduli Biot’s Coefficient Permeability Vp,Vs Failure Criterion s1 Tests with Specimen in Triaxial Cell s1 s1 e1 Failure s2 = constant s2 s2 s1 Single State Triaxial Testing e1 s1 x x x x s2’’’’ s1 x s2’’’ x s2’’ x Tan = Triaxial Factor x s2’ e1 Failure Criterion - Triaxial Factor s2 s1 x s 2’ x s2’’ x s2’’’ x s2’’’’ s1 x x x Tan = Triaxial Factor x e1 s2 Multi-Failure State Triaxial Testing P Wave Velocity at 27.5MPa versus Porosity 9000 Series1 UT MN 1307 P Wave Velocity (m/s) 8000 HRDH 704 7000 HWYH 325 HWYH 394 6000 HWYH 399 5000 4000 3000 2000 y = -111.63x + 6753 1000 R2 = 0.7776 0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Porosity (%) Vp at 27MPa vs Porosity 35.0 Modulus of Elasticity at 27.6MPa versus Porosity Series1 UT MN 1307 HRDH 704 HWYH 325 HWYH 394 HWYH 399 120.00 M odulus of Elasticity (GPa) 100.00 80.00 60.00 y = -1.7701x + 68.839 40.00 R = 0.5076 2 20.00 0.00 0.0 5.0 10.0 15.0 20.0 25.0 Porosity (%) Young’s Modulus at 27 MPa vs Porosity 30.0 35.0 Angle of Internal Friction versus Porosity 70 Series1 Angle of Internal Friction UT MN 1307 60 HRDH 704 HWYH 325 50 HWYH 394 HWYH 399 40 30 20 y = -1.3045x + 49.54 R2 = 0.7722 10 0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Porosity (%) Angle of Internal Friction vs Porosity 35.0 Sampling Rationale - Intact Rock Wireline Log Rock Mechanics Property Correlation Sample Core, then Test Petrophysical Property Populating Model - Intact Rock Correlation Synthetic Rock Mechanics Log Convert Reservoir Characterisation Model into a Geomechanical Model The Process • Populate the Conceptual Model with properties and data • So create a Geomechanical Model of the reservoir (plus surrounding rock) • Impose process-induced changes on the Geomechanical Model using analytical or numerical solutions • Numerical offers more realism than analytical – hence coupled modelling Coupled Modelling More realistic simulation results Fluid Flow Simulator Change in Pore Pressure, Temperature, Saturations Change in Permeability Change in Effective Stresses Rock Movements, Change in Stress and Strain Stress-Analysis Simulator Reservoir and o/b stresses, strains and displacements Enhanced 4D Seismic Interpretation/Reservoir Management Fluid Flow Simulator Change in Pore Pressure, Temperature, Saturations Change in Effective Stresses Differentiating Filter (Synthetic) Saturation-Related changes in Impedance Change in Permeability Stress-Related changes in Impedance Rock Movements, Change in Stress and Strain Changes in Velocity and Density Stress-Analysis Simulator More realistic simulation results Fluid Flow Simulator Change in Pore Pressure, Temperature, Saturations Change in Effective Stresses Enhanced 4D Seismic Interpretation/Reservoir Management Differentiating Filter (Synthetic) Saturation-Related changes in Impedance Change in Permeability Stress-Related changes in Impedance Rock Movements, Change in Stress and Strain Changes in Velocity and Density Stress-Analysis Simulator Reservoir and o/b stresses, strains and displacements Example 1 UKNS, Perm Stress Sensitivity (ECLIPSE coupled with VISAGE) Production Prediction: permeability reduction The diagram shows the absolute reduction (k1k18). The maximum reduction in permeability is in the central part of the field (ECLIPSE Output) 0.39000 k/k0 Perm sensitivity modelled with hysteresis 0.39500 0.38500 Series1 0.38000 0.37500 0.37000 42000 44000 46000 48000 50000 mean stress (kPa) Stress Sensitive Permeability with hysteresis 0.39500 k/k0 0.39000 Injection in Miller induced unloading 0.38500 Series1 0.38000 Depressurisation in Miller 0.37500 0.37000 42000 44000 46000 48000 50000 mean stress (kPa) Injection in South Brae induced unloading in Miller Field Comparison of GOPR Predictions Oil Production Rate is sharply reduced because the permeability reduction in the area causes a reduction in BHP and leads to a increase in gas production (ECLIPSE Output) Horizontal Ground Displacements - 1 Horizontal Ground Displacements - 2 Horizontal Ground Displacements - 3 Stress Ratio vs. time Between wells Close to well Ds 3 3 - Dq / Dp k= = Ds 1¢ 3 + 2 Dq / Dp Stress Status in p-q terms (anisotropy) close to wells far from wells Stress Path Distribution Permeability Stress Path Sensitivity p-q-k 3D MOBIL "U"- Field: Unconsolidated Sand 40 #C4C2P6 q (MPa) #C4C4P1A 100 #C4C2P4 30 20 #C4C5P1 k MATLA B 10 100-200 0-100 N/A(UCMS) 1 S52 <= 40.0 <= 45.0 <= 50.0 <= 55.0 <= 60.0 <= 65.0 S46 <= 70.0 <= 75.0 <= 80.0 <= 85.0 S43 > 100.0 S37 S34 S31p S28 S25 S22 S19 S16 S13 S10 S7 S4 q 61 58 55 52 49 46 43 40 37 34 31 28 25 22 19 16 13 7 10 S1 4 <= 100.0 k/k0 % <= 95.0 S40 1 <= 90.0 S49 90-100 80-90 70-80 60-70 50-60 40-50 30-40 20-30 10-20 0-10 S55 S43 S49 S58 S55 <= 35.0 51 S52 Normalised Permeability Contours <= 30.0 S46 S37 S58 k(%): q 41 S40 P' S31 K stress path sensitive for Unconsolid Sand S34 Mean Ef f ectiv e Stress, p' (MPa) 21 31 S25 50 S28 40 S19 30 S22 20 S13 10 S16 0 S7 0 11 S10 S1 0 S4 Differential Stress, #C4C2P2 61 Excel Compaction and subsidence FE MGV 6.1-02 : H E R IOT-W A TT U N IV E R S ITY 21-JA N -2000 10:53 compac05.cgm Model: MOD L01 L005: TIME /MON TH S * * * * * * * N odal D IS P LA C E Y Max/Min on model set: Max = .504E -3 Min = -.461E -1 Compaction in 1987 1 Y FE MGV 6.1-02 : H E R IOT-W A TT U NIV E RS ITY .2E -1 .15E -1 .1E -1 .5E -2 0 -.5E -2 -.1E -1 -.15E -1 -.2E -1 -.25E -1 -.3E -1 -.35E -1 -.4E -1 X 21-JA N -2000 11:10 compac18.cgm Z Model: MOD L01 L018: TIME /MON THS * * * * * * * N odal DIS P LA C E Y Max/Min on model set: Max = .194E -1 Min = -.339E -1 2 Y Z X .2E -1 .15E -1 .1E -1 .5E -2 0 -.5E -2 -.1E -1 -.15E -1 -.2E -1 -.25E -1 -.3E -1 -.35E -1 -.4E -1 Compaction IN 1995 in which the result of injection is shown Example 2 UKNS, Seismic StressSensitivity (ECLIPSE, VISAGE, HWU software) Features of a 2D flow model grid embedded for coupled geomechanical simulation Overburden Faults Caprock Sideburden Gas , Water in the flow model grid Well Displaced shape of the geomechanical model Surface subsidence Typical location of shear strain on faults Differential compaction across faults in reservoir (VISAGE Output) Mean effective stress distribution at the end of the simulation Unperturbed stress field (constant gradient) Perturbed stress field above and below reservoir Apparent deepening of reservoir due to decreasing pore pressure Localized effects at faults (VISAGE Output) Time-lapsed compressional acoustic impedance Changes in overburden/caprock due to stress redistribution Changes in reservoir Top of caprock due to pore pressure decline Initial gas-water contact Changes in reservoir due to fluid movement (VISAGE Output) Initial Modelling: Before Production Begins Time Lapse Model: Saturation Changes Only Time Lapse Model: Saturation + Stress Time-lapsed seismic trace model Reflector at top of caprock Perturbations at reflector event due to fluid change effects Reservoir top Reservoir base Pull-up in reflector event due to stress change effects Where are we now? • Extreme examples of reservoir stress-sensitivity accepted: Ekofisk, HP/HT, Gulf of Mexico, Angola? • The processes required exist in usable form • Non-uniform levels of commitment • What about the more subtle reservoirs? Technical Challenges • • • • • • Discontinuity distributions Discontinuity properties Rel perm stress-sensitivity In situ stress state Coping with anisotropy Seamless software Organisational Challenges • Realising the full value of the data we already have • Cost vs value of the process • Coping with multi-disciplinarity Is this too much to ask for? Better performance Fully owned decisions Shared belief Shared analysis Decision Making • Straight from the geomechanical model, aided possibly by some calcs, e.g. – fracture density = well locations for max PI – subsidence = yes or no • With the aid of coupled modeling, e.g – improvement of appraisal – impact of perm sensitivity = recovery, GOR etc – Ground movements and subsidence = threat to wells and facilities – 4D seismic enhancement = better management Thank You What do we want to achieve today? • Overview of the main tasks of the project • Select candidate reservoirs for study • Set up communications • Agree next meeting date 17th August? Hysteresis K Increasing Stress Hysteresis K Increasing Stress Hysteresis K Increasing Stress UBD site history very important Effective Stress around the wellbore Failure Level Time Drilling Completion Production Building the Geomechanical Model *Structure and anisotropy analysis from Seismic MultiDisciplinary Tasks assembling data for Model *Published and proprietary studies Basin process simulations *Geomechanical Core Analysis *Log analysis *Geomechanics of fracture genesis *Genetic Units expertise Analogue studies Characterise Structural Setting of the Reservoir Creation of the Geomechanical Model Characterise Reservoir Rocks Characterise Reservoir Faults & Fractures Reservoir Geomechanical Model Stress-Sensitive Coupled Modelling Deliverables feedback to improve characterisation Stress-Sensitive Reservoir Modelling and Coupled Simulations (Ground movements, Fluid Flow and 4D seismic) Better Decisions Reservoir Management feedback to improve characterisation