TOPICS ADDRESSED
The following topics are covered during the course, although not necessarily in the
order given, or with equal weight. The content emphasis can be varied to suit the client,
and problem-solving sessions included.
INTRODUCTION TO PETROLEUM GEOMECHANICS
Introduction to rock mechanics issues in Exploration, Drilling, Completions, Reservoir
Engineering, Waste Management, Underground HC Fluids Storage.
Initial Definitions: Introduction to the concepts of stress and strain in rocks and how
they affect the performance of projects in petroleum engineering
Porosity and Density Calculations: Mineral and pore liquid densities and saturations.
Conversion from porosity to density to void ratio.
The Effective Stress Principle: Total stress, matrix stress, and pore pressure. Why
Petroleum Geomechanics calculations are based on effective stresses.
Design in Petroleum Geomechanics: The six basic design components: in situ state,
behavioral properties, project geometry, past and future history, design calculations,
and verification through monitoring. How the design procedure is implemented for
typical geomechanics problems (reservoir compaction, borehole stability, casing shear).
Uncertainty in geomechanics.
Introduction to Models: Conceptual, physics-based models of processes in Petroleum
Geomechanics. Models of rock behavior (example of elastic models versus others).
ROCK AS AN ENGINEERING MATERIAL: PROPERTIES AND BEHAVIOR
Rock Deformability: Deformation properties, stiffness, compressibility. Stress-strain
and compressibility testing in the laboratory and interpretation of lab data. Typical
deformation properties (Young’s modulus, Poisson’s ratio, compressibility) for shales
and reservoir rocks. Elastic behavior, non-elastic behavior, and plastic behavior.
Viscous behavior of salt, gypsum, and shales.
Rock Strength: Strength properties of shales and reservoir rocks. The concept of
failure and yield. Shear strength, compressive strength, and tensile strength. How to
test rocks for strength behavior. The Mohr-Coulomb yield criterion and its use in rock
mechanics. Brittle and ductile failure, and how rocks behave at various confining
stresses. The behavior of fractured rock.
Rock as a Material: differences between core behavior and rock as a massive body in
the ground. The role of systematic fractures and joints in rock behavior. Does rock
really have a tensile strength? Changes in rock porosity during deformation and failure.
Dilation or contraction during shear displacement?
Transport Processes and Rock Behavior: Pressure, heat, and chemical
concentrations in rock. The concept of a gradient, and how gradients drive flow.
Drained or undrained behavior in shales? Thermal conductivity and thermal expansion
of shales and reservoir rocks.
Rheology Models: Introduction to phenomenological models to analyze rock
response. The elastic spring, the plastic slider, the viscous dashpot, and the brittle
capacitor. Combing these into simple models: the Maxwell material, the Kelvin-Voight
material, the Bingham material. What type of model is best for what Petroleum
Geomechanics conditions?
STRESSES AND SEDIMENTARY BASINS
Stresses as a Basic Input to Rock Mechanics: The nature of stresses and stress
directions. Common assumptions in stress calculations.
Geological History: Burial and compaction of rocks. The effect of geological
diagenesis on rock properties. Burial depth - porosity relationships. Cementation and
density effects on rock strength and deformability. The concepts of overcompaction,
normal compaction and undercompaction.
Natural Stresses: Stresses and pore pressures at depth. Stresses in different
directions and the use of principal stress values. The three types of faults and related
stress regimes. The special growth fault and attendant stress directions.
Basins and Tectonics: Stress magnitudes and directions in various basin types. The
gravity-dominated basin (Gulf Coast, North Slope, North Sea Central Graben, many
continental margin basins). The thrust-dominated basin (Alberta, West Sumatra). The
wrench basin (West California, North Sea Tampen Spur). Mixed basins and stresses.
Stresses and Erosion: Uplifted basins. Development of a simple model for calculation
of stresses because of uplift. Application of the model to real problems in continental
basins.
Stress Measurements: Introduction to the use of hydraulic fracturing and Minifrac™
approaches for measurement of stresses. How reliable are estimates of stresses from
fracturing? Differential strain curve analysis, differential thermal expansion, and other
means of estimating stress directions from core. Use of breakouts, differential log
response, and formation micro-imaging technologies to obtain information on stress
orientation and relative stress magnitudes
Overpressured Zones: The origin and occurrence of overpressured zones. Smectite
transition, thermal pressuring, gypsum-anhydrite transition, undercompaction concept,
etc. Properties of rocks in overpressured zones. The consequences of overpressure
on drilling practices.
MEASURING AND USING ROCK PROPERTIES IN ENGINEERING MODELS
Unconsolidated Sandstone Behavior: The rock mechanics properties of high
porosity sandstones of various types under various stress conditions. Issues of dilation,
contraction, grain crushing, etc.
Fractured Rock Behavior: Mechanical behavior of fractured reservoir rocks, fractured
shales. The change of permeability in fractured systems under stress.
Rock Properties From Geophysical Logs: The uses and limitations of geophysical
logs (gamma, density, sonic, neutron porosity …) for the estimation of rock properties.
Relationships between wave velocities and elastic properties.
Modeling of Stresses and Deformation in Petroleum Geomechanics: Combining
stresses, in situ state, rock properties, geometry, and history into a design.
Approaches to Petroleum Geomechanics Modelling: Deterministic models,
stochastic models (Monte Carlo simulation), conceptual models, mathematical models.
Assumptions and limitations associated with various kinds of models.
Introduction to Mathematical Models: Analytical solutions, semi-analytical solutions,
numerical solutions. Finite Element Method for the solution of stress-strain problems.
Discrete element models for the study of granular materials.
Coupled Flow-Stress Models: Why reservoir simulation in many cases must account
for stress changes as well as pressure changes. How we couple stress-strain models
with reservoir models. Typical problems that coupled models address.
Introduction to Petroleum Geomechanics Monitoring: The limitations of PVT
monitoring through individual wells. The use of deformation monitoring (level surveys
and tiltmeters) to track processes. Microseismic monitoring for reservoir management.
Electrical monitoring using tomographic reconstruction. 3-D and 4-D seismic surveys.
Applications in Exploration: How petroleum gets out or low permeability shales
through induced fracturing. Hydraulic fracturing and the accumulation of gases.
Pressure increases and fault reactivation.
Applications in Drilling: A brief review of the application of rock engineering principles
to the area of well design and drilling engineering. The vital role of lateral stresses, pore
pressures, and shale stability in drilling programs.
Applications in Completions: How hydraulic fractures actually behave, and how
stresses and stress changes control matters. Cement-rock interaction. Perforating and
rock damage.
Applications in Reservoir Management: Sand control, compaction, shear of casing,
thermal processes, etc. all involve massive changes in stresses and sometimes
changes in rock properties. A brief review of these issues is given.
Applications in Waste Management: How to dispose of liquid and solid wastes safely
at great depth without causing induced earthquakes or reservoir impairment. Slurry
fracture injection and salt cavern design and operation for dense slurries of toxic
petroleum industry wastes.
TYPICAL DESIGN PROBLEMS IN PETROLEUM GEOMECHANICS
Calculating Stress Changes and Using a Mohr Diagram: Typical stress changes
near a borehole, in a compacting reservoir, during hydraulic fracture, during faulting.
Plotting stress changes and stress paths on various types of stress charts. What pore
pressure is needed to trigger a fault in various conditions? Comparing a calculated
stress to a rock yield condition.
Predicting Fracture Pressure in Depleted Reservoirs: Use of reservoir depletion
data and rock mechanics to predict depleted reservoir fracture pressure for drilling.
How to drill through depleted zones where circulation loss is a problem.
Reservoir Compaction; Calculations and Design: Introduction to compaction
mechanics. Computations of compaction potential. The use of laboratory and
geophysical data to address a rock mechanics calculation of reservoir behavior. The
change of lateral stress during reservoir compaction. Will the reservoir begin shearing
during compaction? Where can we expect casing shear and other problems around a
compacting reservoir? Pressure maintenance to reduce or eliminate compaction.
Heating or Cooling of a Reservoir: Introduction of heat into a reservoir. Overall
stress changes as the entire reservoir is heated. Cooling and the possibility of hydraulic
fracturing during cold water injection. Stress changes around a circular opening that is
being heated or cooled, and its effects on stability. Stress concentrations between the
reservoir and the overlying rocks, and how this can lead to casing shear or other issues.
ADVANCED STRESS-STRAIN-TRANSPORT AND GEOMECHANICS
Diffusion Mechanics: The four types of diffusive processes: Darcy processes for
advective fluid flow; Fourier processes for the transfer of heat by conduction; Fickian
processes for concentration-gradient processes; Ohmic processes in electrical diffusion.
Coupled Problems: Injection of hot water leads to both Darcy and Fourier transport
processes. Thermal effects can lead to changes in permeability. Other examples of
coupled processes vital to the petroleum industry.
Stresses and Transport: Coupling stress-strain processes (rock mechanics) and
transport processes (Fickian, Darcy, or Fourier processes). What happens if a pressure
change affects the permeability (fracture flow)? What happens if ionic concentration
reduces the strength (shales)?
Some Coupling Effects: A new well test equation accounting properly for the coupling
between stresses and pore pressures. The introduction of coupling into other important
Petroleum Geomechanics processes.
THE FUTURE OF PETROLEUM GEOMECHANICS
CLOSURE: A review of the design approach in Petroleum Geomechanics. How
problem avoidance leads to reduced costs. How to bring rock mechanics principles into
oil field practice. New directions in geomechanics and new areas of application of
geomechanics to improve oil recovery and avoid problems.