AOG Conference Perth, West Australia 23 February, 2017

Transcription

1 Geomechanics Assessment of Depletion (and Injection) Induced Changes: Risks of Reservoir Compaction & Subsidence, Well Integrity, Fault Reactivation & Earthquakes Abbas Khaksar (PhD) Global Geomechanics Advisor Geoscience and Petroleum Engineering, Baker Hughes Inc. AOG Conference Perth, West Australia 23 February, B A K E R H U G H E S I N C O R P O R A TED. A LL R I G H TS R E S E R V E D. TERMS A N D C O N D I TI O N S O F U S E : B Y A C C E P TI N G THIS DOCUMENT, THE RECIPIENT A G R E E S THAT THE DOCUMENT TOGETHER W I TH A LL I N FORMATI O N I N C LUDED THEREIN I S THE C O N FI D E N TI A L A N D P R O P R I E TARY PROPERTY OF B A K E R H U G H E S I N C O R P O R A TED AND INCLUDES VALUABLE TRADE SECRETS AND/OR PROPRIETARY INF ORMA TI O N O F B A K E R H U G H E S (C O LLECTI V E LY "I N FORMATI O N "). B A K E R H U G H E S R E TAINS A LL R I G H TS UNDER COPYRIGHT LAW S A N D TRADE SECRET LAW S O F THE UNITED S TATES OF A M E R I C A A N D O THER COUNTRIES. THE RECIPIENT FURTHE R A G R E E S THAT THE DOCUMENT M A Y N O T B E D I S TRIBUTED, TRANSMITTED, C O P I E D O R R E P R O D U C E D I N W H O LE OR IN P A R T B Y A N Y M E A N S, E LECTRONIC, MECHANICAL, O R O THERWISE, W I THOUT THE E X P R E S S P R I O R W R I TTEN C O N S E N T O F B A K E R H U G H E S, A N D M A Y N O T B E U S E D D I R E C TLY OR INDIRECTLY I N A N Y W A Y D E TRIMENTAL TO BAKER HUGHES INTEREST.

2 Geomechanical Model Definition of Geomechanics Geomechanics is the study of Earth stresses and mechanical properties of rocks at their current states, their changes and their effects Present-day geological structures (folds, faults, fractures, etc.) are the consequence of the past stresses which may not be active today Oilfield operations, and hence behaviour of reservoir and cap rocks, faults, etc. are strongly influenced by the present-day stress state S v Geomechanical modelling is therefore the basis for understanding rock behaviour and developing solutions for drilling, completion, stimulation and exploitation of conventional & unconventional reservoirs: to avoid hazards, increase efficiency and optimize production, safely and economically - Pore pressure - Rock mechanical properties - In situ stress orientations & magnitudes 2 - Faults and fractures

3 Where and When is Geomechanics Needed in Oil Fields?.. From appraisal-to-abandonment.. 1D to 4D and well-to-field applications 3

4 Geomechanical Modeling, Workflow and Input Data Drilling & Production Data mud weights/ecd, survey, drilling history & events, XLOT/XLOT, Pp data, DST, production info Core Data Routine &SCAL UCS, TWC, PSD, thin section, SEM, dispersion, chemical Well Logs Caliper, Gr, Rhob, Acoustic, image, NME, dipmeter, MWD/ LWD Update the model with new data Geomechanical Model stress magnitudes & orientation, pore pressure & rock strength Geolo. Geophys. & Petrophy. Seismic, Tectonic history, sediment., analogs, etc. Stress changes with depletion & injection Pp Prediction Wellbore Stability Hydraulic fracturing & Injection Sanding Prediction Compaction & Subsidence Fault seal & Fracture Permeability and Seismicity 4 Field Development and Reservoir Management

5 Stress Magnitude Depletion Effect on Stresses Reservoir In the reservoir section, the magnitude of the horizontal stresses reduces as the reservoir depletes. For a a laterally long layer-cake homogeneous reservoir the stress path parameter (ΔS h /ΔP p ) can be determined from poroelastic equations or field scale numerical modelling, both require calibration with field data. Pore Pressure & Stress Pore Pressure & Stress Vertical Stress (S v ) S h P, H p P p S h Fracking data ( ) showed that stress path factors varies in different locations of the field. 5 Depletion Stress profile of infill wells after depletion.

6 Potential Depletion Effect on Reservoir and Overburden Fault reactivation due to Depletion Reservoir compaction, surface subsidence compression and shear damage within production interval shearing at the top of production/injection zones localized horizontal shear at weak lithology interfaces within the overburden Subsidence Depth Compaction Reservoir Diameter Thickness H 6 After M.B. Dusseault et al. (2001) Casing Shear: Causes, Cases, Cures

7 Casing Damage from Compaction Shear damage in overburden Buckling damage in reservoir Example casing deformation patterns from Ekofisk Field (SPE 28091) ~10m compaction, ~3.7m surface subsidence 7

8 Example of Subsidence- Ekofisk, North Sea Example: Ekofisk, North Sea Cost estimate: Due to sea bed subsidence, the Ekofisk complex in the North Sea was sinking by approximately 40cm/yr and had reduced the safety air gap of 20m to 16.3m between the platform decks and storm waves. In order to compensate for the subsidence of six platforms, the jack up project was born with a criteria to create a 23m 100 year design wave by extending the platform legs and raising the decks 6m. This was the largest lift and most prestigious project in the world at the time with a total value of 400 million, and for IMH Commissioning Engineers the most challenging and rewarding undertaken at that time Platform-Field-Subsidence.pdf 8 Compaction and Subsidence can be predicted and modelled with a reasonable accuracy

9 Model Calibration for Subsidence and Compaction Subsidence (surface data) Onshore, subsidence can be calibrated with surface data (GPS, InSAR monitoring ) Offshore, regular bathymetric surveys or platform positioning (GPS, InSAR) 9 Compaction (downhole measurements) Compaction calibration requires downhole measurement. CMI - radioactive bullet placed in the formation with regular spacing. Sureview Wire monitoring - optic fibers clamped on a casing Modelled subsidence Comparison with surface data

10 Real Time Compaction Monitoring (RTCM) How it Works: Thousands of Fiber Brag Grating on a fiber Each FBG responds individually to strain Software combines the information and creates a 3D image Directly measures axial strain, radius of curvature of bend and crushing Characteristic response differentiates the mode of deformation Axial compression (compaction) & tension Bending, Ovalization, Shearing a b c Figure 8. Unique signatures are seen for Shearing a) pure axial strain, b) bend our buckle, c) and shearing. Pure Axial Strain Bend or Buckle 10

11 *All vertical scales x10 exaggerated Modelling of Compaction and Subsidence Case Study from South East Asia Business motivations: 1) Loss of permeability due to pore collapse 2) Platform subsidence 3) Fault permeability after depletion / re-injection Zone of interest 11 8 major reservoirs are constrained with 3 major faults. 6 individual structural models are available for the reservoir sections. R6 has been in water/gas injection for EOR since R4 and R5 are planned to be injected for EOR from 2017.

12 Simulation Results: Compaction and Subsidence (strain) 2016 Baker Hughes Incorporated. All Rights Reserved. *All vertical scales x10 exaggerated Total subsidence 12 Compaction of individual layers with depletion and injection

13 Casing Deformation Simulation- Depleting Reservoir Local submodel are built along the actual well trajectories based on the casing string design. The pore pressure and displacement obtained from the 4D dynamic model are used as boundary conditions for driving the casing deformation simulation in the submodel. Rock Casing (4-6 layers) 4D GEM D01 Cement (4-6 layers) Submodels C3 D8 Cement Casing 13

14 Casing Deformation with Depletion (m) Original Location 31 Dec 2035 reservoir Highest stress exceeds the casing yield stress. (Pa) The modelled highest stress will cause less than ~0.5% plastic strain at the end of field life. If this level of plastic strain is allowable, the current casing rating would be safe during the production. 14

15 Fault Reactivation and Seismicity Due to Excessive Injection Oklahoma s recent earthquakes are associated with saltwater injection (disposal pf produced water from oil wells) Increase of seismicity follows 5-10 fold increase in rates of water disposal The disposal formations are connected to active faults in crystalline basement. Map of Earthquakes & Injection in Oklahoma 15 From Walls & Zoback 2015

16 4D Geomechanical Modelling of Fault Stability SAGD Example, Canada Reservoir top Reservoir bottom 16

17 Tau Ratio (Cap Rock Integrity) Reservoir top Reservoir bottom 17

18 Future Applications: Earthquake Hazard Risk Assessment Probability of Failure x Consequences of Failure? Challenges: Events with low probability of occurrence and extreme outcomes Earthquakes Uncertainty and complex, highly non-linear relationships in often data sparse environments complex systems almost always fail in complex ways Solutions: Develop a robust understanding of relevant data Enable access to data and visualisation Target data collection to improve reliability 18

19 Acknowledgement My colleagues at Baker Hughes: Dr. Ahmadreza Younessi Dr. Ramon Guises Dr. Feng Gui Dr. Adrian White 19