Time-Lapse Gas Geochemistry and EoS Modeling for Reservoir Desorption
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Solution Overview
Problem
Existing methods struggle to accurately determine the quantity and behavior of desorbed gas in unconventional hydrocarbon reservoirs, such as shale rocks and coal beds, due to the equilibrium between free and adsorbed gas, making it difficult to estimate critical parameters and validate numerical models for gas desorption during pressure depletion.
Innovation Solution
A method involving fluid sampling, isotope analysis, and equation of state (EoS) calibration is employed to determine the desorption stage and quantity of desorbed gas by measuring isotope ratios and calibrating the EoS using fluid samples taken at different times, allowing for the prediction of gas components and critical pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fluid sampling and basic composition analysis are used, then the measurement process is simple, but the precision of desorbed gas quantity determination is insufficient
Solution Approach 1:
The patent segments the gas analysis into multiple components: free gas measurement, adsorbed gas measurement through desorption, and isotopic composition analysis. Each segment addresses a specific aspect of the desorbed gas determination, allowing precise measurement while managing system complexity through modular analysis approaches
Solution Approach 2:
The patent introduces an equation of state model as an intermediary between raw measurements and desorbed gas quantity determination. This model integrates fluid composition data, pressure depletion information, and isotopic ratios to calculate desorbed gas quantities, bridging the gap between simple measurements and complex reservoir characterization
2Measurement precision
If fluid samples are taken at multiple time points for EoS calibration, then the accuracy of gas component prediction improves, but the time required for analysis increases
Solution Approach 1:
The patent performs preliminary Equation of State calibration using initial fluid samples before production depletion occurs. This preliminary action establishes baseline parameters that can be used to predict gas composition changes over time, reducing the need for frequent re-sampling and analysis while maintaining prediction accuracy
Solution Approach 2:
The patent implements a feedback mechanism where measured gas compositions from production are compared against EoS predictions. Discrepancies provide feedback to refine the model parameters, improving prediction accuracy over time without requiring proportional increases in sampling frequency
3Measurement precision
If isotope ratios and multiple fluid properties are measured, then the ability to determine desorption stage improves, but the complexity of the measurement system increases
Solution Approach 1:
The patent employs a multi-functional analysis system that simultaneously measures isotopic ratios, gas composition, and fluid properties from the same sample. This universal approach determines desorption stage, characterizes gas composition, and validates reservoir models using a single integrated measurement platform, reducing overall system complexity despite the sophistication of individual measurements
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 precise estimation of desorbed gas quantities and critical pressures, improving reservoir property assessment and optimizing production strategies for unconventional reservoirs by enhancing the accuracy of gas-in-place and ultimate recovery calculations.
Implementation Method 1
determining an equation of state with the fluid property and the composition of the first fluid sample
Implementation Method 2
determining a measured relative volume of gas components and isotope ratios of gas components of the first fluid sample
Implementation Method 3
Gas adsorbed onto the surface of the grains is in equilibrium with free gas in the shale pores
Implementation Method 4
the gas is composed of free gas contained within pore space and adsorbed gas associated to the surface of grains
Data Source
AI summary
Methods and systems for determining an estimated reservoir property using a determined desorption stage are disclosed. The method includes determining a fluid property and composition of a first fluid sample obtained from a reservoir, determining a measured relative volume of gas components and isotope ratios of gas components of the sample, and determining an equation of state. The method also includes obtaining a second and third sample at two later times, determining a composition, a measured relative volume of gas components, and isotope ratios of gas components of the later samples, and calibrating the equation of state utilizing the fluid composition and measured relative volume of gas components. The method further includes predicting a relative volume of gas components from the equation of state, determining a desorption stage, determining a critical pressure, an extent of desorption and a quantity of produced desorbed gas and determining the estimated reservoir property.