Shale Oil Alternating CO2–Nitrogen Displacement for Injection Control
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Solution Overview
Problem
Current research lacks effective methods for simulating and optimizing the injection volume of carbon dioxide and nitrogen for alternate displacement of shale oil, which affects oil displacement efficiency and porosity changes in shale reservoirs.
Innovation Solution
A simulation analysis method involving pretreatment of shale cores, sequential injection of carbon dioxide and nitrogen, and measurement of NMR T2 spectra to calculate oil displacement efficiency and porosity changes, ultimately building an expression for adjusting the injection volume based on these parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carbon dioxide injection volume is increased to improve oil displacement efficiency, then oil recovery increases, but carbon dioxide usage volume increases and cost increases
Solution Approach 1:
The patent implements alternate displacement cycles where carbon dioxide and nitrogen are injected in sequence rather than continuously. The injection process follows periodic cycles: CO2 injection phase, nitrogen injection phase, followed by production phase. This periodic action allows the system to maintain displacement efficiency while reducing overall CO2 consumption by using nitrogen to sustain pressure and continue driving oil toward production wells during non-CO2 injection periods.
Solution Approach 2:
The patent changes the physical parameters of the displacement system by introducing nitrogen gas with different properties compared to carbon dioxide. Nitrogen has lower solubility in oil and different viscosity characteristics. By alternating between these two gases with different parameters, the system optimizes displacement efficiency while controlling CO2 usage. The parameter change from pure CO2 displacement to alternate CO2-N2 displacement allows reduction of CO2 volume while maintaining or improving recovery.
2Productivity
If multiple alternate displacement cycles are performed to improve oil displacement efficiency, then oil recovery increases, but porosity changes occur in the shale core
Solution Approach 1:
The patent implements a feedback mechanism where porosity changes are monitored during alternate displacement cycles. NMR (nuclear magnetic resonance) technology is used to detect porosity variations in real-time. Based on the feedback from porosity measurements, the injection parameters such as pressure, temperature, and gas volumes are adjusted to maintain porosity stability while continuing to improve oil displacement efficiency. This closed-loop control prevents excessive porosity changes that could damage the shale structure.
Solution Approach 2:
The patent employs dynamic adjustment of injection parameters based on the evolving state of the shale core. As displacement cycles progress and porosity begins to change, the system dynamically modifies injection rates, pressures, and the ratio of CO2 to nitrogen volumes. This dynamic approach allows the system to adapt to porosity changes and maintain optimal displacement conditions throughout the extended multi-cycle process, balancing productivity improvement with structural stability.
3Quantity of substance
If nitrogen is introduced as an inert gas for alternate displacement, then carbon dioxide usage is reduced, but the complexity of the displacement process increases
Solution Approach 1:
The patent segments the displacement process into distinct phases: CO2 injection phase, nitrogen injection phase, and production phase. Each phase has specific operational parameters and objectives. This segmentation allows for systematic control and monitoring of each gas injection process separately, making the overall complex process more manageable. The clear phase division helps in optimizing each segment independently while maintaining overall system efficiency.
Solution Approach 2:
The patent maintains continuous useful action by ensuring that while CO2 injection is paused, nitrogen injection continues the displacement process. The nitrogen acts as a bridge between CO2 injection cycles, maintaining reservoir pressure and continuing to drive oil toward production wells. This continuity eliminates idle periods and ensures that the displacement process remains productive throughout, reducing the need for frequent restarts and simplifying overall process control despite the multi-gas system.
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 method improves the accuracy of real-time oil displacement efficiency monitoring and adjusts the injection volume to enhance oil recovery, reducing carbon dioxide usage and optimizing shale oil production.
Implementation Method 1
injecting carbon dioxide gases and nitrogen gases in sequence... calculating a curve area difference between the NMR T2 spectrum B and the NMR T2 spectrum A at a same coordinate
Implementation Method 2
the strong adsorption of CO2 in organic matter
Implementation Method 3
measuring an NMR (nuclear magnetic resonance) T2 spectrum A in an initial state... measuring an NMR T2 spectrum B when an air pressure is balanced
Implementation Method 4
heating to a set temperature, saturating the shale core with crude oil at the set temperature and the set pressure
Implementation Method 5
vacuumizing the pretreated shale core... vacuumizing a current shale core obtained by the step (4) again
Data Source
AI summary
A simulation analysis method for an injection volume of alternate displacement of shale oil by carbon dioxide and nitrogen includes steps of simulating the alternate displacement of shale oil by carbon dioxide and nitrogen for multiple times through the core displacement simulation experiment, measuring the oil displacement efficiency change for every time, obtaining the porosity change in the entire displacement process through the porosity change before and after alternate displacement, and building the injection volume adjustment expression of alternate displacement of shale oil by carbon dioxide and nitrogen as a reference of the injection volume of alternate displacement of shale oil by carbon dioxide and nitrogen, so that the total displacement efficiency in the actual mining process is improved, thus increasing the production rate of shale oil and reducing the usage amount of carbon dioxide. A simulation analysis device is used to carry out the simulation analysis method.