4D Seismic Analysis for Hard Rock Reservoirs
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Solution Overview
Problem
Current methods for interpreting 4D seismic data in hard rock formations face challenges in accurately predicting fluid saturation and pressure changes due to weak seismic signals, which complicates reservoir monitoring and hydrocarbon extraction planning.
Innovation Solution
The method involves analyzing seismic data from hard rock formations by defining intervals with specific permeability levels, applying different rock physics relationships based on permeability ranges, and inferring fluid saturation or pressure changes using 4D seismic attributes, which are then used to verify and modify reservoir simulation models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional rock physics relationships are applied to hard rock formations, then the method is simple to implement, but the prediction accuracy of fluid saturation and pressure changes deteriorates due to weak seismic signals
Solution Approach 1:
The patent applies different rock physics relationships based on permeability ranges. For high permeability formations, one set of relationships is used, while for low permeability formations, another set is used. This parameter change approach allows the method to adapt to different formation conditions, improving prediction accuracy without significantly increasing implementation complexity
Solution Approach 2:
The method dynamically selects which rock physics relationships to apply based on the permeability characteristics of the formation being analyzed. This dynamic adaptation allows the system to optimize its performance for different scenarios (high vs. low permeability) while maintaining a unified method framework
2Productivity
If 4D seismic data is used to monitor reservoir changes, then real-time reservoir surveillance is enabled, but the signal strength deteriorates in hard rock formations making detection difficult
Solution Approach 1:
The patent changes the approach by selecting different rock physics relationships based on permeability. For low permeability hard rock formations where seismic signals are weak, the method uses specific relationships that are more sensitive to fluid and pressure changes, thereby improving detection capability despite the weak signals
Solution Approach 2:
The patent uses permeability information as an intermediary to select appropriate rock physics relationships. This intermediary parameter allows the system to bridge the gap between weak seismic signals and accurate reservoir parameter estimation by choosing relationships that are most suitable for the given formation characteristics
3Adaptability or versatility
If fluid mixing patterns are modeled using conventional approaches, then the theory is well-established, but the applicability deteriorates for low permeability rocks where fluid movement is restricted
Solution Approach 1:
The patent changes the rock physics relationships based on permeability ranges. For low permeability formations, it uses relationships that account for restricted fluid movement and patchy saturation patterns, while for high permeability formations, it uses relationships assuming more uniform fluid mixing. This parameter change ensures reliable modeling across different permeability conditions
Solution Approach 2:
The patent applies different rock physics relationships to different permeability zones within the reservoir. By recognizing that low permeability and high permeability areas have different fluid mixing characteristics, the method locally optimizes the rock physics relationships for each zone, improving overall model reliability
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 optimally evaluates dynamic reservoir properties, improving the accuracy of fluid and pressure change predictions even under weak 4D signal scenarios, enhancing hydrocarbon extraction planning and reservoir management.
Implementation Method 1
The changes in reservoir fluid saturation, pressure and temperature that occur during production also induce changes in the reservoir acoustic properties of rocks that under favorable conditions may be detected by seismic methods
Implementation Method 2
Using different forms of approximations of the reflectivity equation and a rock physics model, a set of coefficients can be estimated to make a combination of near and far difference amplitudes
Implementation Method 3
The mixing pattern of the two fluids is in turn influenced by the permeability at a given frequency (e.g. seismic frequency) (Batzle et al. 2006). For low permeability rocks, fluids can not move easily as in the higher permeability rock
Data Source
AI summary
A method including analyzing seismic data relating to a producing hydrocarbon reservoir is disclosed. The seismic data includes first and second sets of seismic data obtained at different times. An interval composed substantially of hard rock is identified in the hydrocarbon reservoir. 4D seismic attributes for the region are calculated. Rock physics relationships are applied to seismic data related to the interval according to the permeability associated therewith. A fluid saturation change or a pressure change of the interval is inferred based on outputs of the first or second sets of rock physics relationships and the calculated 4D attributes for the interval. The inferred fluid saturation change or pressure change of the interval is outputted.