Equivalent Black Oil Model for Compositional Grading
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Solution Overview
Problem
Existing methods for estimating fluid properties in hydrocarbon reservoirs, such as black oil models, are computationally expensive and may not accurately account for compositional grading, leading to inaccuracies in reservoir performance predictions.
Innovation Solution
The development of a system and method to determine an equivalent black oil model by extracting properties from a fully compositional simulation model, converting them into a two-dimensional PVT table, and iteratively refining the black oil model to match the compositional model's results using an equivalency metric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fully compositional model is used to estimate reservoir fluid properties, then measurement precision and reliability are improved, but productivity deteriorates due to computational expense requiring ten hours or more to complete calculations
Solution Approach 1:
The patent creates a simplified black oil model that copies the essential PVT behavior of the complex compositional model. By extracting PVT properties from compositional model calculations and representing them in simplified black oil tables, the system replicates the accurate fluid behavior predictions while enabling much faster computational performance suitable for real-time or near-real-time reservoir evaluation.
Solution Approach 2:
The patent replaces the expensive, computationally intensive compositional model with a cheaper black oil model that uses simplified PVT tables. This substitution sacrifices some computational complexity but maintains sufficient accuracy for reservoir evaluation, enabling rapid calculations that can be performed repeatedly during production planning and optimization.
2Productivity
If a conventional black oil model with compositional gradient is used, then productivity is improved through faster calculations, but measurement precision deteriorates resulting in larger volume differences and inaccurate field performance predictions
Solution Approach 1:
The patent transforms the compositional model's three-dimensional PVT properties into two-dimensional black oil PVT tables by changing the parameter representation. This conversion involves extracting key PVT parameters from the compositional model and organizing them into depth versus saturation pressure or depth versus solution gas ratio relationships, enabling the black oil model to accurately represent compositional variation while maintaining computational efficiency.
Solution Approach 2:
The patent applies compositional grading locally within the black oil model by imposing depth-dependent PVT properties. Instead of using a single set of PVT parameters for the entire reservoir, the system assigns different PVT tables to different depth intervals, capturing the local compositional variations that affect fluid behavior while keeping the overall model structure simple and computationally efficient.
3Device complexity
If compositional variation with depth is imposed using depth versus saturation pressure or depth versus solution gas ratio, then device complexity is reduced, but manufacturing precision deteriorates in high compositional variation reservoirs leading to larger volume differences
Solution Approach 1:
The patent performs preliminary calculations using the compositional model to extract accurate PVT properties before initializing the black oil model. By pre-calculating the PVT tables from compositional model results and storing them for use in the black oil simulations, the system ensures that the simplified model starts with accurate, compositionally-graded PVT data, eliminating the need for complex runtime compositional calculations while maintaining precision.
Data Source
AI summary
Systems and methods of determining an equivalent black oil model are disclosed. In one embodiment, a method of determining an equivalent black oil model of a reservoir includes generating three-dimensional PVT properties using a compositional model, calculating original fluid in place and reservoir performance characteristics from the three-dimensional PVT properties, and converting the three-dimensional PVT properties to a two-dimensional PVT table. The method further includes, until an equivalency metric is satisfied, generating one or more grouped PVT property tables, initializing a black oil model with the one or more grouped PVT property tables, calculating estimated fluid in place and estimated reservoir performance characteristics using the black oil model, and comparing the estimated fluid in place and the estimated reservoir performance characteristics with the original fluid in place and the reservoir performance characteristics to determine whether the equivalency metric is satisfied.