Unstructured Grid Transmissibility Calculation
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Solution Overview
Problem
Current methods for determining transmissibility in numerical simulation of oil and gas reservoirs on unstructured grids are inadequate, as they lack a practical method to calculate transmissibility between adjacent grids, especially considering directional permeability and anisotropy, which is essential for simulating complex well trajectories and geological features.
Innovation Solution
A method is developed to calculate transmissibility between unstructured grids by determining centroid distances, seepage direction vectors, effective seepage areas, and directional permeability using core seepage experimental data and well logging data, employing a Scheidegger model to account for directional permeability, and then applying these parameters to a transmissibility model.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a generic mathematical expression for transmissibility is used, then the formulation is simple, but the method is difficult to apply due to lack of practical calculation guidance
Solution Approach 1:
The patent segments the transmissibility calculation into distinct, manageable components: determining centroid coordinates, calculating seepage direction vectors, computing effective seepage areas, and applying directional permeability through the Scheidegger model. This segmentation transforms the complex mathematical expression into a step-by-step practical guide for calculation.
Solution Approach 2:
The patent introduces intermediary concepts such as seepage direction vectors and effective seepage areas as mediators between the grid geometry and the permeability properties. These intermediaries bridge the gap between mathematical formulation and practical application, enabling systematic calculation of transmissibility in unstructured grids.
2Measurement precision
If isotropic permeability is used, then the calculation is simplified, but the simulation accuracy deteriorates due to inability to account for directional permeability and anisotropy
Solution Approach 1:
The patent applies local quality by introducing directional permeability that varies with orientation. Instead of using a single isotropic permeability value, the method calculates permeability in specific directions (x, y, z) using the Scheidegger model, allowing different permeability values for different flow directions at each grid location, thereby accurately representing anisotropic reservoir properties.
Solution Approach 2:
The patent changes the permeability parameter from a scalar isotropic value to a directional tensor that depends on the seepage direction vector. By using direction cosines and the Scheidegger model, the permeability parameters are transformed to reflect actual directional flow characteristics, improving simulation accuracy for complex well trajectories and geological features.
3Adaptability or versatility
If unstructured grids are used, then the grid flexibility and adaptability improve, but the transmissibility determination becomes unavailable or inaccurate
Solution Approach 1:
The patent achieves universality by developing a general method that works for any unstructured grid configuration. The approach uses centroid coordinates and seepage direction vectors that can be calculated for any grid topology, making the transmissibility determination method universally applicable to complex reservoir geometries while maintaining reliability through systematic calculation procedures.
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 accurate and reliable transmissibility values, verified by rectangular grid examples, enabling effective simulation of complex oil and gas reservoirs with improved accuracy and practicality for field applications.
Implementation Method 1
determining a directional permeability KL in the seepage direction between the adjacent unstructured grids with a Scheidegger model KL=Kx cosαL+Ky cosβL2+Kz cosrL2
Data Source
AI summary
The present invention relates to development research of oil and gas fields, and more particularly to a method for determining transmissibilty in numerical simulation of oil and gas reservoirs on unstructured grids. Based on the core seepage experimental data and well logging data of the drilled wells, the method takes into account the centroid distance of two adjacent grids as well as seepage direction vectors in the oil and gas reservoir simulation, and then adopts effective seepage area and directional permeability of the interface between the adjacent grids in seepage direction to calculate the transmissibilty. The present invention further verifies the reliability of the method by a rectangular grid example (rectangular grid is a special case of unstructured grids) whose accurate transmissibilty values can be obtained. The method of the present invention is simple, easy to understand and realize, operable, effective and practical.