Sequential Implicit Reservoir Model for Heterogeneous Horizontal Wells
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Solution Overview
Problem
Existing well models, such as explicit or semi-implicit models, fail to produce accurate flow profiles in highly heterogeneous reservoirs with vertically non-communicating layers, leading to incorrect flow profiles and simulator convergence issues, especially when dealing with hundreds of vertical layers and multiple wells.
Innovation Solution
A reduced well model system is formed by combining vertically communicating layers into single layers, allowing for matrix computation using a direct sparse solver to determine bottom hole pressure and completion rates, which are then used to solve the full reservoir model, thereby improving computational efficiency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If simple explicit or semi-implicit well models are used, then computational simplicity and low cost are achieved, but accuracy of flow profiles is lost in highly heterogeneous reservoirs with vertically non-communicating layers
Solution Approach 1:
The patent segments the reservoir into communicating and non-communicating layers, applying different modeling approaches to each segment. Communicating layers use simple explicit models while non-communicating layers use fully implicit models, resolving the contradiction by localizing complexity only where needed.
Solution Approach 2:
The patent applies different model complexities to different spatial locations within the reservoir. Simple models are used in homogeneous regions while fully implicit models are used in heterogeneous regions with flow barriers, achieving accuracy where needed without unnecessary complexity elsewhere.
2Measurement precision
If fully implicit fully coupled well models with simultaneous solution are used, then accuracy and numerical stability are improved, but computational expense increases significantly
Solution Approach 1:
The patent divides the reservoir into zones requiring different levels of modeling complexity. Only zones with vertically non-communicating layers use the computationally expensive fully implicit models, while other zones use simpler models, dramatically reducing overall computational expense while maintaining accuracy where needed.
Solution Approach 2:
The patent applies the full complexity of fully implicit modeling only partially - specifically to the extent necessary for handling non-communicating layers - rather than applying it universally throughout the entire reservoir model, thus avoiding excessive computational expense.
3Measurement precision
If the number of vertical layers is increased to represent reservoir heterogeneity, then modeling accuracy is improved, but device complexity and computational burden increase
Solution Approach 1:
The patent segments the large number of vertical layers into groups based on vertical communication characteristics. By treating layers within each segment collectively rather than individually, the model maintains the ability to represent heterogeneity while reducing the effective complexity of the system.
Solution Approach 2:
The patent merges multiple vertically communicating layers into single equivalent layers in regions without flow barriers. This combining reduces the total number of layers and model complexity while preserving the essential heterogeneity characteristics through aggregated properties.
Data Source
AI summary
A subsurface hydrocarbon reservoir with horizontal wells is simulated by sequential solution of reservoir and well equations to simulate fluid flow inside the reservoir and well production rates. Sequential solution of reservoir and well equations treats wells as specified bottom hole pressure wells. This avoids solving large matrices resulting from the simultaneous solution of the reservoir and well equations which can be computationally very expensive for large number of unknowns and require special sparse matrix solvers. Such sequential solution involves regular reservoir system solvers complemented by a small matrix for the numerical solution of the well bottom hole pressures.