Practical Aspects of Shale Gas Geomechanics

Introduction to shale gas geomechanics – business drivers …

Basics of Rock Mechanics includes - concept of stress/strain; definition of elastic properties, Young’s modulus, Poisson’s ratio, bulk modulus, shear modulus, bulk compressibility; rock strength – UCS, tensile strength and shear strength; yield, failure and failure criteria

Exercise 1

• shear and normal stress calculations,
• effect of pore pressure

Laboratory Rock Mechanics - testing geometries and interpretation of test results. Computation of mechanical properties; and strength parameters from logs; why difference between dynamic and static properties; converting dynamic to static, calibrating mechanical properties.

Exercise 2

• Compute mechanical properties from logs
• Interpret and analyze mechanical core tests
• Calibrate mechanical properties

Understanding Earth Stresses includes - concept of principal stresses; are principal stresses always vertical and horizontal?; in-situ stresses - overburden stress, minimum and maximum horizontal stresses: magnitude and orientation; stress regimes – is vertical stress always the maximum?; pore pressure and principle of effective stress; estimating stresses from wire line logs; calibration of in-situ stresses; borehole breakouts, drilling-induced tensile fractures, use of image logs in understanding stress orientation and anisotropy; how does stress help orient wellbore and completions; stress measurement using mini-frac/LOT/MDT; basic definitions of fracture gradient, break down pressure, fracture propagation pressure, closure pressure and other terminologies used in LOT/XLOT.

Exercise 3

• Compute stresses from logs and calibrate using mini-frac data

Pore pressure - Origins of pore pressure, methods for measurement, estimation of pore pressure in shales, equivalent depth methods, Eaton’s method, real-time approach for drilling

Wellbore Stability – Basics includes - state of stress around the wellbore; stress state & drilling hazard; what is wellbore failure and types of failures; failure criteria, and prediction of the mud weight window.

Exercise 4

• Estimation of pore pressure using equivalent depth
• Compute stresses around a borehole
• Estimate safe mud weight window

Mechanical Earth Modeling includes - recommended data acquisition program for an effective geomechanics analysis; introduction to building Mechanical Earth Model (MEM): why and how is it used?; types of MEM, input data, deformation mechanisms; integrating log data, core data and field stress measurements in MEM.

Shale Anisotropy and Heterogeneity includes - characterizing shale from geomechanics perspective; shale anisotropy – micro-scopic to core to field scale; how to evaluate it?; evaluating TIV anisotropy, scratch testing and variation in mechanical properties in vertical and horizontal directions;

Anisotropy and Stress in Shales – anisotropic stress models; acoustic anisotropy; estimating anisotropic parameters using acoustic azimuthal anisotropy (Sonicscanner).

Exercise 5

• Compute stresses using anisotropic mechanical properties
• Compare with isotropic stresses

Drilling through Shale includes -  effect of intrinsic anisotropy, bedding planes and natural fractures; transversely isotropic and anisotropic models in wellbore stability analysis; geomechanical considerations for drilling high angle and horizontal wells through laminated shale..

Hydraulic fracturing and Shale stimulation - theory of hydraulic fracturing, how fractures are created/initiated, fracture growth; fracture height and width, preferential direction, vertical and horizontal fracs, and frac barriers; parameters controlling frac geometry; fractured reservoirs: influence of natural fractures on fracturing; frac fluid and proppant properties.

Introduction to Microseismics - hydraulic fracture performance evaluation; introduction to microseismic and hydraulic fracture monitoring (HFM); field examples on hydraulic fracturing and horizontal completions in shale gas reservoirs.

Interaction between natural and induced fractures – the effect of natural fractured formations on hydraulic fracturing

Exercise 6

• Hydraulic fracture propagation in a naturally fractured formation