4D Seismic Velocity Monitoring for Fracture Network Characterization
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Solution Overview
Problem
Characterizing the distribution of injected gas in hydraulically fractured laterals for enhanced oil recovery (EOR) is challenging due to poor seismic amplitude indicators, leading to inefficiencies and dry holes, as low gas saturations produce similar seismic responses to high gas saturations.
Innovation Solution
Employing time-lapse seismic surveys to track changes in seismic velocities and elastic properties associated with gas injection, enabling characterization of fracture networks and fluid saturation changes, thereby optimizing gas injection efficiency and hydrocarbon recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional seismic amplitude and AVO methods are used to detect gas presence, then gas presence can be identified, but measurement precision of gas saturation is poor because low and high gas saturations produce comparable seismic responses
Solution Approach 1:
The patent changes the measured parameter from seismic amplitude to seismic velocity. By monitoring velocity changes before and after gas injection, the method achieves precise gas saturation measurement because velocity is directly affected by gas presence in fractures, unlike amplitude which remains ambiguous at low saturations.
Solution Approach 2:
The patent replaces the traditional amplitude-based detection mechanism with a velocity-based detection mechanism. This substitution involves using 4D seismic velocity monitoring instead of amplitude analysis, enabling accurate characterization of gas distribution and fracture networks through velocity perturbations caused by gas injection.
2Productivity
If gas injection EOR is performed without accurate characterization, then enhanced oil recovery can be attempted, but productivity is reduced due to inefficient gas distribution and dry holes
Solution Approach 1:
The patent implements a feedback mechanism by conducting 4D seismic surveys at multiple time points (pre-injection, during injection, and post-injection). This temporal feedback allows real-time monitoring of gas distribution, enabling operators to optimize injection strategies and avoid dry holes by identifying areas where gas has not effectively reached fractures.
Solution Approach 2:
The patent performs preliminary 4D seismic characterization before gas injection to identify existing fracture networks and their properties. This preliminary action allows for better planning of injection strategies, ensuring that gas is injected into areas with effective fracture networks, thereby improving overall recovery productivity and reducing the risk of dry holes.
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 approach reduces uncertainty in determining effective stimulated rock volume and injection conformance, improving well spacing and production interventions, and enhancing hydrocarbon recovery by accurately mapping fracture networks and gas contact areas over time.
Implementation Method 1
seismic amplitudes and amplitude versus offset response (AVO) are strong indicators of the presence of gas in a reservoir system
Implementation Method 2
track changes in seismic velocities and elastic properties associated with gas injection
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
A method of characterizing a subterranean formation using a plurality of seismic acquisitions includes obtaining a first seismic acquisition of the subterranean formation, wherein the first seismic acquisition is a baseline survey. Injecting a gas fluid into the subterranean formation, wherein the gas fluid at least partially fills a portion of a fracture network of the subterranean formation. Obtaining a second seismic acquisition of the subterranean formation. Calculating a time-lapse difference in the plurality of seismic acquisitions.