Technology of Production from Shale

Transcription

1 Technology of Production from Shale Doug Bentley, European Unconventional, Schlumberger May 29 th, 2012 Johannesburg, South Africa

2 What are Unconventional Reservoirs Shale both Gas & Oil Coal Bed Methane -CBM Tight Gas Gas Hydrates

3 What are Shale Reservoirs Organic Rich Shale Source Rocks Surrounding poor quality rock ignored as non economic in the past. Porosity sources are mostly unconventional Matrix Rock has Very Low Permeability Require Hydraulic Stimulation to make productive

4 Shale Exploration -Starting Point Devon Energy have used Petroleum Systems Modeling to build their acreage position in a North American shale gas play: Petroleum Systems Modeling Modeled variability of the gas adsorption and saturation thresholds as a function of temperature, maturity, and kinetic scheme through space and time by means of a 3D numerical simulation of hydrocarbon generation and expulsion Based on these results it was possible to select sweet spot locations to be leased for this project, consequently minimizing the lease and exploration costs Mosca et al. (2010) 3D Petroleum Systems modeling applied to unconventional shale gas play: prediction of sweet spots based on areal and depth distribution of sorption capacity in shale gas. Abstract AAPG Annual Convention and Exhibition, New Orleans, April, 2010.

5 Understanding Reservoir & Completion Quality Reservoir Quality Maturity Organic Content Porosity Permeability Water Saturation Pressure Gas in Place Completion Quality Stress Anisotropy Fracture Containment Near & Far Field Stress Clay Content & Type Fabric Pattern Mineral Sensitivity Wellbore Placement

6 Shale Gas Reservoir Quality - Maturity Control Petrology Tectonic subsidence (burial depth timing) Diagenesis (cements, clay, organics)

7 Shale Gas Reservoir Quality Organic Content & Porosity Conventional sandstone Mineral framework Gas shale Kerogen 700 mm Pore system Free gas in pore space 100 mm Free gas in pore space Adsorbed gas on kerogen 7

8 Shale Gas Reservoir Quality Permeability E E+006 Well GAS Production Rate, Mscf/d Km = md Km = md 1.6E E E+006 1E Well GAS Cumulative Production, Mscf Cumulative Time

9 Shale Gas Reservoir Quality Saturation Perm (nd) R² = Sw

10 Shale Gas Reservoir Parameter Ranges Sample No A-R Bulk Density A-R Grain Density Dry Grain Density Porosity Water Saturation Gas Saturation Mobile Oil Saturation Gas- Filled Porosity Bound Hydrocarbon Saturation Bound Clay Water Pressure Decay Perm (g/cm 3 ) (g/cm 3 ) (g/cm 3 ) (% of BV) (% of PV) (% of PV) (% of PV) (% of BV) (% of BV) (% of BV) (md) (wt %) Effective phi: 4 to ~12 pu Saturations: S liquid < 45% Permeability: > 100 nd TOC: > 2 wt% TOC

11 Shale Gas Reservoir Pressure Measurement Wireline Pumpout module Pressure gage Inflate seal valve P Packer Interval seal valve P 1m 3ft 6000 Interval Pressure (psi) 0.50 Packer Pressure (psi) 0.45 Packer Sliding coupling Flow control module Sample chamber P Pressure, psi Injection Rate (gal/min) Rate, gpm Time, min

12 Shale Gas Reservoir Pressure Measurement Eight Hour Shut-in 35 psi Run Sensitivity during Closure Estimate pressure at psi/ft Gradient used to estimate Gas in Place, assuming Saturated System

13 Shale Gas Reservoir Gas in Place Gas in Place Calculated from CBM Standard BCF per Sq Mile TOC is considered Saturated for most cases as we are well over 1000 psi in most wells. Effective porosity is used with estimated pore pressure. Gas in Place is Integrated over total Shale bottom to top of interval. Examples: Core Barnett 139 BCF/ Sq Mile Marcellus 60 BCF/Sq Mile Haynesville 129 BCF/Sq Mile Adsorbed Gas Content, scf/ton Methane Adsorption Isotherms (as a function of Total Organic Carbon) ,000 1,200 Pressure, psia Total Organic Carbon= 16 % 14 % 12 % 10 % 8 % 6 % 4 %

14 Shale Gas Core Calibrated Reservoir Quality GR Resistivity Porosity RHOB RHOM ECS / XRD ELAN Sw Porosity TOC Perm GIP Gas-Phi

15 Shale Gas Completion Quality Mechanical Properties Shale can be very anisotropic due to laminations and bedding (especially expandable clays or organic) TIV Transverse Isotropic with Vertical axis of symmetry Shale, laminated sands Comp. Vertical Velocity Not the Same!! Comp. Horizontal Velocity

16 Shale Gas Completion Quality Anisotropic Properties Fast Strong 16 Slow Weak

17 Shale Gas Completion Quality Anisotropic Stress Overburden Argillaceous Shale Bed E h = 6 x 10 6 psi E v = 3 x 10 6 psi n h = 0.26 n v = 0.25 Siliceous Shale Bed E h = 8 x 10 6 psi E v = 6 x 10 6 psi n h = 0.16 n v = 0.13 Argillaceous Shale: Isotropic: σ h = 0.66 psi/ft Anisotropic: σ h = 0.87 psi/ft Siliceous Shale: Isotropic: σ h = 0.53 psi/ft Anisotropic: σ h = 0.57 psi/ft Anisotropic shale properties increases stress in argillaceous intervals

18 Shale Gas Completion Quality Fracture Containment GR Res. f D & f N Mineralogy Isotropic & Anisotropic Closure Stress Closure Stress Swelling Clays = High Closure Stress High Silica Volume = Low Closure Stress High Clay Volume = High Closure Stress Carbonates my be High or Low Closure Stress

19 Shale Gas Completion Quality Clay Volume - Good relationship between the clay volume and the difference between the Anisotropic and Isotropic closure stress models Total Clay Volume - Correlation is weakest at low clay volumes where the rocks are more isotropic - Increasing the clay volume increases the error in the isotropic stress model Difference in Anisotropic and Isotropic Stresses

20 Shale Gas Completion Quality Clay Type Swelling Clay Volume - Excellent relationship between the volume of swelling clay and the difference between the Anisotropic and Isotropic closure stress models - Small amounts of swelling clays dramatically increase closure stress -Not captured with Isotropic models Difference in Anisotropic and Isotropic Stresses

21 Shale Gas Completion Quality Role of Fabric Rock fabric can be very complex Fractures can be open, healed, drilling induced or reactivated Clay is usually found in layers Mud systems need to limit activation of healed systems All planes of weakness need to be mapped Regional stress needs to be understood

22 Shale Gas Completion Quality Creating Surface Area Creating Productive Surface Area 3D Stress Mapping Complex Hydraulic Fracture Simulations

23 Shale Gas Completion Quality Maintaining Surface Area 20/40 Resin Coated Sand Argillaceous Facies Post-Conductivity Testing Fracture Face Image 20/40 Sand Siliceous Facies

24 Shale Gas Completion Quality Maintaining Surface Area Key elements Improved fracture clean-up Low risk of screenout Results of Channel Fracturing Reductions in water of 25% and proppant of 42% Production: 20-50% increase Longer effective fracture halflengths Proppant placement rate: 99.96%

25 Shale Gas Completion Quality Well Placement 4100 Frac Half Length Propped Frac Half Length 4200 Upper Shale Lower Shale 4300 TVD - - ft ft 4400 Argillaceous Lower Shale Lower Boundary Stress - psi Width at Wellbore - min Fracture Half Length - min

26 Reservoir & Completion Quality - Summary Shale is heterogeneous at all scales Reservoir Quality and Completion Quality can be defined. Data integration is used to define and exploit the reservoir. Production improvements come from many things Well placement where conductivity to the developed fracture system can be developed and maintained. Large surface area contained in the reservoir. Propprant concentrations placed to maintain surface area and minimize pinch points in the reservoir. Water flowback program to minimize reservoir damage and fines production. Stimulation fluids program to limit Chemo-mechanical weathering.