Nitrogen-Assisted CO2 Fracturing for Shale Oil Recovery
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Solution Overview
Problem
The development of shale oil reservoirs is hindered by extremely low permeability and water sensitivity, making conventional methods like water flooding ineffective, and carbon dioxide injection fracturing faces challenges in capture and transportation costs, limiting its economic efficiency.
Innovation Solution
An integrated method of nitrogen-assisted carbon dioxide fracturing, where carbon dioxide is initially injected to form fractures, followed by nitrogen to push carbon dioxide deeper into the reservoir, with shut-in and production cycles optimized to maximize gas usage and recovery efficiency, while maintaining reservoir pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carbon dioxide injection fracturing is used to develop shale oil reservoirs, then oil recovery efficiency is improved, but transportation cost and capture complexity increase
Solution Approach 1:
The patent introduces nitrogen as an intermediary gas to assist carbon dioxide injection. Nitrogen is first injected into the reservoir to create pressure and open fractures, then carbon dioxide is injected through these pre-opened fractures. This intermediary approach reduces the direct complexity of carbon dioxide capture and transportation by using nitrogen as a preparatory medium that facilitates subsequent carbon dioxide injection.
Solution Approach 2:
The fracturing process is segmented into two distinct stages: first nitrogen injection to create fractures and establish pressure pathways, then carbon dioxide injection to interact with crude oil. This segmentation allows each gas to perform its specific function optimally - nitrogen for fracture creation and carbon dioxide for oil recovery - thereby reducing the overall complexity of the carbon dioxide capture and injection system.
2Productivity
If carbon dioxide injection fracturing is used to develop shale oil reservoirs, then oil recovery efficiency is improved, but transportation cost increases
Solution Approach 1:
The patent applies partial action by using nitrogen for the initial fracture creation and pressure establishment, then following with carbon dioxide injection. This partial use of nitrogen (only for the preparatory phase) reduces the total quantity of carbon dioxide that needs to be transported and injected, thereby lowering transportation costs while still achieving effective oil recovery through the subsequent carbon dioxide injection.
3Productivity
If nitrogen is injected to push carbon dioxide deeper into the reservoir, then gas contact with crude oil is improved, but nitrogen consumption increases
Solution Approach 1:
The patent establishes continuity of useful action by injecting nitrogen and carbon dioxide in a continuous sequence rather than separately or intermittently. The nitrogen injection creates continuous pressure and opens fractures, followed immediately by continuous carbon dioxide injection through the same pathways. This continuous action ensures maximum gas-crude oil contact efficiency while optimizing the ratio of nitrogen to carbon dioxide consumption.
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 enhances oil recovery by fully contacting carbon dioxide with shale oil, reducing viscosity, and maintaining reservoir pressure, thereby improving the economic and operational efficiency of shale oil development.
Implementation Method 1
the injected carbon dioxide gas reacts with the formation water in the oil reservoir to generate carbonated water which corrodes the nearby formation and improves the formation permeability
Implementation Method 2
In well shut-in, the nitrogen diffuses to the deeper formations with the carbon dioxide. Due to the low solubility of nitrogen in crude oil, nitrogen can maintain the formation pressure, thereby increasing the elastic energy of the formation
Implementation Method 3
fracturing is applied in shale oil formation to generate fractures of different directions and lengths in the formation, so that the injected gas can pass along the fractures to the deeper reservoir
Data Source
AI summary
The invention discloses an integrated method for nitrogen-assisted carbon dioxide fracturing and development of shale oil reservoirs, comprising the following steps: fracture the target shale reservoir with nitrogen-assisted carbon dioxide; after fracturing, firstly inject carbon dioxide gas into the target shale oil reservoir, and then inject nitrogen gas to push the carbon dioxide gas into the further location of the oil reservoir; shut in the well in the target shale oil reservoir; after shut-in, open the well to implement depletion production; after the first cycle of production, the slug volume of the injected gas and the shut-in time are 1.5 times of those in the previous cycle in the subsequent production, and Steps 5 to 7 are repeated for each cycle. The present invention maximizes the recovery efficiency of shale oil reservoirs; in this way, carbon dioxide gas can be used most efficiently, making the development of shale reservoir more economical and efficient; the integrated fracturing and development design enables the field operation to be streamlined and standardized, and thus different departments to cooperate each other closer.