Fracture Mechanics in Petroleum Geomechanics

Study of the propagation of cracks in rocks and its application to petroleum geomechanics
Essential to understand the behavior of fractures in reservoirs and their impact on hydrocarbon production

Stress Intensity Factor (SIF): a measure of the stress at the tip of a crack
Fracture Toughness: the ability of a rock to resist fracture propagation
Critical Stress Intensity Factor (KIC): the minimum SIF required to initiate fracture propagation

Energy Release Rate (G): the energy available to drive fracture propagation
Fracture Propagation Criterion: a condition that must be met for fracture to propagate, e.g. G ≥ Gc (critical energy release rate)

Hydraulic Fracturing: fracture propagation induced by fluid injection to enhance hydrocarbon production
Fracture Network Analysis: study of fracture networks in reservoirs to understand their impact on fluid flow and hydrocarbon recovery
Wellbore Stability: analysis of fracture propagation around wellbores to prevent wellbore instability and ensure safe drilling operations

Fracture mechanics involves studying the propagation of cracks in rocks and its application to petroleum geomechanics to understand behavior of fractures in reservoirs and their impact on hydrocarbon production.

Stress Intensity Factor (SIF) measures the stress at the tip of a crack and is used to predict fracture propagation.
Fracture Toughness is the ability of a rock to resist fracture propagation and is a critical parameter in evaluating rock strength.
Critical Stress Intensity Factor (KIC) is the minimum SIF required to initiate fracture propagation and is a key parameter in evaluating fracture behavior.

Mode I fracture involves opening mode (tensile loading) and is the most common type of fracture.
Mode II fracture involves sliding mode (shear loading) and occurs when there is a shear stress acting parallel to the fracture plane.
Mode III fracture involves tearing mode (out-of-plane shear loading) and occurs when there is a shear stress acting perpendicular to the fracture plane.

Energy Release Rate (G) is the energy available to drive fracture propagation and is a critical parameter in evaluating fracture behavior.
Fracture propagation occurs when the energy release rate (G) meets or exceeds the critical energy release rate (Gc), which is the minimum energy required to initiate fracture propagation.

Hydraulic Fracturing is a process where fracture propagation is induced by fluid injection to enhance hydrocarbon production from low-permeability reservoirs.
Fracture Network Analysis is the study of fracture networks in reservoirs to understand their impact on fluid flow and hydrocarbon recovery.
Wellbore Stability involves analyzing fracture propagation around wellbores to prevent wellbore instability and ensure safe drilling operations.

Wellbore stability is the ability of a wellbore to maintain its shape and structure during drilling, completion, and production operations.
It is crucial for ensuring safe and efficient oil and gas production.
Wellbore instability can lead to costly repairs, lost production, and even catastrophic failures.

In-situ stresses: Three principal stresses (σv, σH, σh) can cause instability if not properly managed.
Rock properties: Mechanical properties such as Young's modulus, Poisson's ratio, and cohesion influence wellbore stability.
Pore pressure: Changes in pore pressure can alter the effective stress on the wellbore, leading to instability.
Drilling fluid properties: Type and properties of drilling fluids can affect wellbore stability, particularly in shale formations.
Wellbore trajectory: Direction and inclination of the wellbore can impact stability, with horizontal wells being more prone to instability than vertical wells.

Breakout: Formation of a cavity or void in the wellbore wall, often due to excessive stress concentrations.
Collapse: Inward collapse of the wellbore, typically caused by excessive compressive stress or low rock strength.
Sloughing: Shedding of rock fragments or cuttings from the wellbore wall, often due to drilling fluid-related issues.
Borehole oscillations: Unstable oscillations of the wellbore, which can lead to fatigue and failure.

Optimize drilling fluid properties: Selecting the right drilling fluid type and properties can help maintain wellbore stability.
Manage in-situ stresses: Understanding and managing the in-situ stress regime can help prevent wellbore instability.
Select suitable wellbore trajectory: Choosing an optimal wellbore trajectory can reduce the risk of instability.
Monitor and analyze wellbore data: Real-time monitoring and analysis of wellbore data can help identify potential instability issues before they become critical.
Implement wellbore strengthening techniques: Techniques such as casing and cementing can help strengthen the wellbore and prevent instability.