Fracture Height Prediction in Multi-Layer Formations
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Solution Overview
Problem
Existing methods for predicting fracture height during fracturing stimulation in multi-layer formations are inadequate, as they fail to account for factors like multi-layer formation, multiple fractures, tip plasticity, and formation stress, leading to inaccurate predictions and increased risks.
Innovation Solution
A method that calculates displacement discontinuity quantities and induced stress using the displacement discontinuity method, combined with the equilibrium height theory and stress intensity factor calculations, to accurately predict fracture height, considering the influence of adjacent fractures and rock mechanics parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear elastic fracture theory is used to predict fracture height, then the calculation is simple, but the prediction accuracy is poor because it does not account for tip plasticity and stress concentration effects
Solution Approach 1:
The patent transitions from linear elastic fracture theory parameters to elastoplastic fracture theory parameters, incorporating tip plasticity zone size and stress concentration factors. This changes the fundamental parameters of the prediction model to account for non-linear behavior at fracture tips, thereby improving accuracy while maintaining computational feasibility through established elastoplastic models.
2Device complexity
If the influence of adjacent artificial fractures is not considered, then the prediction model is simpler, but the prediction accuracy deteriorates due to ignoring stress interference between multiple fractures
Solution Approach 1:
The patent divides the multi-fracture system into individual fracture segments, each with its own stress field characteristics. By segmenting the complex multi-fracture interaction problem into manageable individual fracture analyses, the model can systematically account for stress interference between adjacent fractures while maintaining computational tractability through modular calculation approaches.
Solution Approach 2:
The patent introduces stress interference factors as intermediary parameters that mediate the interaction between adjacent artificial fractures. These stress interference factors serve as quantitative descriptors of the complex stress field interactions, allowing the model to account for multi-fracture influences without requiring direct simulation of all fracture interactions, thus balancing accuracy and complexity.
3Ease of operation
If conventional fracture height prediction methods are used that ignore multi-layer formation characteristics, then the calculation is straightforward, but the prediction accuracy is insufficient for complex multi-layer reservoirs
Solution Approach 1:
The patent incorporates the vertical dimension of multi-layer formation structures into the prediction model by considering fracture propagation across different geological layers with varying mechanical properties. This dimensional expansion from single-layer to multi-layer analysis allows the model to account for layer-specific stress fields, rock mechanics variations, and fracture propagation constraints imposed by different formation characteristics, thereby improving accuracy for complex multi-layer reservoirs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method provides a more accurate and efficient prediction of fracture height, applicable to multiple layers, accounting for stress concentration effects and rock plasticity, thereby reducing risks and improving the accuracy of fracture propagation analysis.
Implementation Method 1
A displacement discontinuity method (DDM) may be used to divide each fracture into m displacement discontinuity units, and a displacement discontinuity quantity of each unit of each fracture may be calculated
Implementation Method 2
due to a stress concentration effect, a plastic zone appears at fracture tips
Implementation Method 3
pref is a pressure at a depth of a middle portion of a perforation (Pa); dmid is a depth of a middle portion of the fracture (m)
Implementation Method 4
g is an acceleration of gravity (m/s2)
Implementation Method 5
a plastic zone appears at fracture tips. This results in that the linear elastic fracture theory is no longer applicable
Data Source
AI summary
The present invention discloses a method for predicting fracture height during fracturing stimulation in multi-layer formation, comprising specific steps of: (1) acquiring basic parameters; (2) calculating a displacement discontinuity quantity of an artificial fracture; (3) calculating induced stress generated by the fracture; (4) calculating stress intensity factors at a fracture tip without considering a fracture tip plasticity; (5) calculating sizes of a plastic zone; (6) calculating stress intensity factors at the fracture tip considering the plastic zone; and (7) judging a relationship between the stress intensity factors and a fracture toughness. The present invention is suitable for multiple stratums, and the influences of parameters of tip plasticity, induced stress, crustal stress, and rock mechanics are considered so that a calculation result is more accurate and calculation efficiency is higher.