Subsurface Gas Desorption Modeling with 3D TOC Mapping
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Solution Overview
Problem
Existing methods fail to accurately model gas desorption in subterranean reservoirs, particularly in unconventional resources like coal and organic-rich shale, which is crucial for estimating the economic viability and production forecasting of these resources.
Innovation Solution
A method involving measuring gas sorption parameters, generating a 3D distribution of total organic carbon (TOC), estimating the original adsorbed gas in place (OAGIP) using a Langmuir isotherm, and predicting gas desorption based on a defined desorption pressure, allowing for both saturated and under saturated mechanisms to be modeled.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional gas storage modeling methods are used, then the modeling process is simple, but the accuracy of gas desorption estimation is insufficient for unconventional resources
Solution Approach 1:
The patent applies preliminary action by pre-defining desorption pressure thresholds and pre-calculating Langmuir isotherm parameters before actual production forecasting. This allows the model to be ready with pre-computed sorption characteristics, enabling accurate gas desorption estimation without complex real-time calculations during production analysis.
Solution Approach 2:
The patent utilizes parameter changes by incorporating pressure-dependent sorption parameters and transitioning between different desorption mechanisms (saturated vs. under-saturated) based on reservoir pressure conditions. The model dynamically adjusts gas storage capacity parameters as pressure changes, enabling accurate representation of gas desorption behavior in unconventional resources.
2Reliability
If a comprehensive 3D distribution model is created, then the reliability of reservoir engineering analyses is improved, but the computational requirements and data processing complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the reservoir into discrete 3D grid cells, each with its own TOC value and gas storage characteristics. This segmentation allows the model to handle complex spatial variations in organic content while maintaining computational tractability through cell-by-cell calculations rather than continuous mathematical modeling.
Solution Approach 2:
The patent uses copying by creating a digital 3D representation of the reservoir's TOC distribution from well log data and core samples. This digital copy enables repeated analysis and forecasting without requiring physical reservoir modification, and allows the same spatial distribution data to be used across multiple engineering analyses (production forecasting, history matching, EUR estimation).
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
Enables accurate estimation of original gas in place (OGIP), enhancing the reliability of reservoir engineering analyses such as history matching and production forecasting, and improving the assessment of organic-rich reservoirs.
Implementation Method 1
Adsorption at a gas/solid interface can be referred to as the enrichment of one or more components in an interfacial layer. For example, the organic matter in a shale has a strong adsorption potential due to large surface area and an affinity to methane.
Implementation Method 2
predicting the amount of gas desorbed from the subterranean reservoir as the reservoir is depleted
Data Source
AI summary
Systems and methods for modeling gas desorption in a subterranean reservoir include measuring a gas sorption parameter using a crushed core sample from the subterranean reservoir; computing a gas storage capacity of the subterranean reservoir at an initial reservoir pressure based on the gas sorption parameter; generating a three-dimensional (3D) distribution of total organic carbon (TOC) in the subterranean reservoir; estimating a 3D distribution of original adsorbed gas in place of the subterranean reservoir by correlating the gas storage capacity with the 3D distribution of TOC; and predicting the amount of gas desorbed from the subterranean reservoir as the reservoir is depleted.