Volumetric Fracturing Simulation for Dual Medium Reservoirs
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Solution Overview
Problem
The high construction pressure in unconventional dual-medium reservoirs during volumetric fracturing leads to ineffective expansion of hydraulic fractures, and existing models treat these reservoirs as conventional single media, affecting calculation accuracy and fracture initiation behaviors due to neglect of natural fractures and complex fracture interactions.
Innovation Solution
A fracture viscoelastic-plastic damage model and grid units with explicit time integral are developed to simulate the stress, seepage, and flow fields, allowing for discrete natural fracture generation and embedding fracture units to model the complex expansion and interaction of hydraulic and natural fractures, optimizing perforation and construction parameters for effective fracture extension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional single-medium models are used to treat unconventional dual-medium reservoirs, then the model complexity is reduced, but the calculation accuracy of fluid pressure distribution and fracture initiation behavior deteriorates
Solution Approach 1:
The reservoir is segmented into two distinct media: the matrix medium and the fracture network medium. Each medium is modeled separately with its own governing equations and properties, allowing the complex dual-medium system to be divided into manageable components that can be solved independently and then coupled together.
Solution Approach 2:
The patent applies composite material modeling by treating the dual-medium reservoir as a composite system consisting of matrix blocks and fracture networks. Different constitutive models are assigned to each medium type, and their interactions are captured through interface conditions, enabling accurate representation of the heterogeneous reservoir structure.
2Strength
If high construction pressure is applied during volumetric fracturing, then the fracturing process can overcome reservoir strength, but the reservoir construction pressure exceeds the limit causing serious accidents and ineffective fracture expansion
Solution Approach 1:
The patent changes the approach from controlling only pressure magnitude to controlling multiple parameters including pressure, injection rate, and timing. By adjusting these parameters dynamically and optimizing the fracturing sequence, the system achieves effective fracture initiation and propagation without exceeding safe pressure limits.
Solution Approach 2:
The patent implements preliminary actions by creating access channels through matrix fracturing before attempting to propagate fractures through the full reservoir thickness. This preliminary fragmentation reduces the required pressure for subsequent main fracture propagation and prevents pressure buildup that could lead to accidents.
3Area of stationary object
If multi-cluster perforation is used for volumetric fracturing, then the fracture network coverage is increased, but the near-well zone fractures become complex causing sand blockage
Solution Approach 1:
The multi-cluster perforation system is segmented into distinct fracturing stages and zones. Each cluster is treated as an independent unit with controlled fracture propagation, preventing the development of complex interconnected fracture networks that lead to sand blockage while maintaining adequate coverage.
Solution Approach 2:
Different fracturing strategies and parameters are applied to different clusters and zones within the reservoir. Local geological conditions are considered, and fracturing parameters are optimized for each specific location, ensuring effective coverage without creating uniformly complex fracture patterns throughout the entire wellbore.
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 approach reveals the mechanisms of fracture rejection, attraction, bifurcation, and intersection, enabling the formation of dominant main fractures and optimizing the fracturing process to reduce near-well friction drag and enhance fracture connectivity, thereby improving the accuracy of fluid pressure distribution and fracture initiation.
Implementation Method 1
a fracture viscoelastic-plastic damage model and grid units of an explicit time integral are constructed
Implementation Method 2
a fracture viscoelastic-plastic damage model and grid units of an explicit time integral are constructed
Implementation Method 3
grid units of an explicit time integral are constructed
Implementation Method 4
the mechanism of influences of the natural fracture layout and parameters, perforation parameters, liquid type and displacement lifting methods on rejection, attraction, bifurcation and intersection of multiple hydraulic fractures and natural fractures in the cluster is revealed
Data Source
AI summary
A numerical simulation and parameter optimization method for volumetric fracturing of an unconventional dual medium reservoir includes the following steps: based on the theory of dual-medium pore elasticity, in consideration of the friction effect between fractures, developing a viscoelastic-plastic damage model of hydraulic fractures based on explicit time integral; simulating random intersection and bifurcation of hydraulic fractures encountering with natural fractures by adopting a method of embedding zero-thickness fracture units in the inner boundaries of computational model grids, and establishing a mathematical model of hydraulic fracture expansion of volumetric fracturing in the unconventional dual-medium reservoir; compiling a finite element program for complex multi-fracture fracturing and competitive expansion during volumetric fracturing of the unconventional reservoir, and establishing a hydraulic fracturing finite element model of a casing-cement ring-perforation hole in cluster-reservoir matrix containing natural fractures.