Petroleum Geomechanics for Shale Gas

Petroleum Geomechanics for Shale Gas Prof. Lyesse LALOUI Chair Professor «Gaz Naturel» Ecole Polytechnique Fédérale de Lausanne, EPFL Acknowledgement: V. Favero, A. Ferrari, L. Chao

Unconventional Gas Shale Gas 2

Unconventional Gas Shale Gas Shale gas may create 100,000 jobs in France. Challenges, September14 th 2012 3

Unconventional Gas Reservoir Characteristics Low values of porosity (between 3% and 7%) Source: Investigating the Microstructure of Gas Shales by FIB/SEM Tomography & STEM Imaging Mark E. Curtis, Raymond J. Ambrose, Carl H. Sondergeld, and Chandra S. Rai University of Oklahoma Ant 5 mm Human hair 50 μm Low values of water saturation (between 10% and 50%) High values of negative water pressure (High Suction) Red blood cells 2-5 μm Atoms of silicon 10 nm 5

Unconventional Gas Reservoir Characteristics Conventional and unconventional gases differ not by their chemical compositions (all these resources are natural gas) but rather by the geological characteristics of their reservoir rock. Permeability Challenges: Rock (matrix) permeability and porosity in unconventional reservoirs are much lower than for conventional reservoirs. Fracturing as a solution: As a result, unconventional reservoirs only have commercial potential if the rock is fractured. Total, 2012 Natural and created fractures enhance flow potential but the location and properties of underground fractures are difficult to measure or forecast. 6

Hydraulic Fracturing Injection of water sand and additives under pressure. Additives protect the wellbore from corrosion and improve the effectiveness of the fracture stimulation. Strong chemical composition: chemoosmotic phenomena in Shales can be of primary importance. Source: Drilling and completing shale gas wells, horizontal drilling and well construction. New Brunswick. 7

State officials acknoledge that they have little information about the scale or practice of fracking in California. Los Angeles Times, April 1 st 2012 We come across new questions The Injected pressure must be greater than the horizontal stress in Shales but how greater? How does the gas permeability evolve after fracturing during gas extraction? Need to test under stress and negative water pressure (suction) control. 8

Geomechanical behaviour of shales A multiphysical research approach Mechanics Constitutive laws, stress redistribution, stiffness and strength variations, self sealing capacity Hydraulics Changes in saturation state, retention properties, capillary effects, hysteretical behaviours, permeability dependency on the degree of saturation, Temperature Thermal conductivity, thermal gradients, thermal fracturing Chemistry Changes in pore fluid composition Chemical weathering 9

Osmotic efficiency Ion diffusion rate Geomechanical behaviour of shales A multiphysical research approach T Heat conduction Thermal conductivity Heat convection C Chemo-osmotic processes Heat convection Thermal conductivity Specific heat Fluid density Fluid viscosity Osmotic efficiency Porosity H Water and gas flow Porosity M Stress-strain framework Effective stress Suction change Dessication cracks THCM behaviour an exhaustive characterization of the behavioural features of shales requires to deal simultaneously with four major physical aspects and their coupled interactions Experimental testing must be collected to assess the material response related to each physical aspect and the coupled effects Porosity Osmotic suction 10

Experimental representation in laboratory FACTS CHALLENGING IN-SITU CONDITIONS High temperatures: may reach 100 C High pressures: dozens of MPa s 11

Retention properties of shales OCR=1 Los Angeles Times, April 1 st 2012 Accumulation of irreversible settlements. 12

Retention properties of shales Opalinus Clay Retention Properties at Different Temperatures - EPFL 4MPa T= 21 C T= 21 C T= 21 C AEV 80 C 1MPa T= 80 C T= 80 C T= 80 C The water retention capability of the soil is reduced by an increase in temperature A faster decrease of the void ratio can be observed with the higher temperature. A decrease of the air-entryvalue with suction is observed 13

Void ratio High pressure Oedometer testing 1 Main features 2 3 2 2 4 Max. vertical stress 100 MPa Independent control of pwp at the two bases (0 2 MPa) Vertical stress (log) 1. Saturation at constant volume (synthetic water) 2. Loading/unloading cycles 3. Assessment of the initial yield stress 4. Assessment of the NCL Available layouts for temperature control (4 120 C) and suction control (4 400 MPa) 14

High pressure oedometric tests on Shales Test results: evaluation of the compressibility The mechanisms of subsidence Source: US geological survey Most of the deformation takes place in the reservoir layers 15

Void ratio [-] Void ratio [-] High pressure oedometric tests on Shales Test results Suction effects Ambient temperature Temperature effects Suction = 4 MPa 0,18 0,18 0,17 0,16 0,16 0,14 0,15 0,14 0,13 0,12 0,12 0,1 0,08 T = 22 C T = 80 C 0,11 s = 15 MPa s = 20.2 MPa 0,1 0,001 0,01 0,1 1 10 100 Total stress [MPa] 0,06 0,04 0,1 1 10 100 Total stress [MPa] 16

High pressure oedometric tests on Shales Test results: evaluation of Shale permeability Source: Investigating the Microstructure of Gas Shales by FIB/SEM Tomography & STEM Imaging Mark E. Curtis, Raymond J. Ambrose, Carl H. Sondergeld, and Chandra S. Rai University of Oklahoma K c v w E oed Good estimation of the coefficient of permeability can be achieved. 17

Experimental tools THMC 18

Geomechanics Through the Life of a Reservoir Harvest Subsidence, Induced Seismicity, Approach Horizontal drilling, Wellbore stability.. Development Injected pressure, Fracture Stimulation, Appraisal Initial stress estimation, Pore pressure prediction, 19

THMC Behaviour of Geo-Materials Reservoir Material Behaviour involved in engineering issues Several areas of the Oil & Gas industries involve Thermo-Hydro-Mechanical Chemo (THMC) problems related to reservoir geo-materials. Stress redistribution, Thermal impact, Chemical effect, Approach Horizontal drilling, Wellbore stability.. Development Injected pressure, Fracture Stimulation, Harvest Subsidence, Induced Seismicity, Appraisal Initial stress estimation, Pore pressure prediction, Saturation/Desaturation, Capillary forces, Self-sealing capacity, 20

Advances in Testing the Hydro-Mechanical Behaviour of Shales A comprehensive analysis of shale behaviour requires different physical aspects and the coupled effects to be investigated Collecting proper experimental evidence for shales requires specific apparatuses and techniques Collected experimental results are used for the development of a comprehensive THM(C) constitutive modelling framework First fracture stimulation from 1949 in Grant County, Kansas 21