|Alternative Title||Microscopic Seepage Mechanism of Water Flooding by Using Pore-Fracture dual Network Modeling|
|Place of Conferral||北京|
|Keyword||孔隙-裂隙双重网络模型 微观渗流机理 驱油效率 应力敏感性 动态裂缝|
Dual porous media is the reservoir with multi-scale of pore and fracture structure. The two-phase seepage in dual porous media is a typical problem in the exploitation of low-permeability, tight oil and gas. The existence of micro-fractures have many influences on the reservoir. On the one hand, it can increase the number of channels with low resistance in the reservoir and improves the permeability; on the other hand, it will lead to the fluids preferentially flow through the micro-fractures, resulting in the decrease of the sweep efficiency and the displacement efficiency. Therefore, the microscopic seepage characteristics of the fractured dual porous media are important in the microscopic seepage mechanics and oil/gas resource exploitation.
The purpose of pore-scale modeling based on percolation theory is to predict the properties which are difficult to measure laboratory experiments and in-situ tests, such as relative permeability, sweep efficiency, displacement efficiency, etc. according to the available core data (e.g. pore structure) and fluid parameters (e.g. fluid viscosity, density, etc.) .In addition, changes in flow characteristics can be easily predicted by the model when the pore structure and the fluid properties change.
In this dissertation, the research work of the pore-fracture dual network model was summarized first. A dual network model based on pore and fracture statistics data of cores was established considering the dynamic cracking of micro-fractures. A set of experimental methods were established to study the relationship between mechanical properties and the stress sensitivity of cores, and the effects of fractures generation on the stress sensitivity. The dynamic cracking in micro-fractured cores was also studied by experiments. By numerical simulation and physical experiments, the influences of the microscopic percolation characteristics of water flooding were obtained, such as the changes of the distribution of fluid pressure in the pores, the dominant flow channels, the oil utilization rate and the relatively permeability curves.
The main innovations achieved in this dissertation are as follows:
(1) The distribution of pore and fracture were obtained by using nuclear magnetic resonance and micrometer CT. Based on the statistics data of real cores pore and fracture and flow mechanism in throats and micro-fractures, a pore-fracture network model considering various micro-fracture parameters was established. The dimensionless parameters in the problem were proposed. A series of simulations were carried out and the influences of the dimensionless parameters on the percolation was obtained, which can be used for tight reservoirs with micro-fractured networks (Chapter 2).
(2) The influences of fracture factors (e.g. length, density, direction, position and gap, the fractal parameters of the micro-fracture length) on the absolute permeability and oil displacement efficiency were investigated. The reason for the occurrence of water channeling and dead oil zones in the reservoir due to the presence of fractures was found. (Chapter 3).
(3) A set of experimental methods for studing the stress sensitivity of porous media containing micro-fractures were proposed. The stress-strain relationship (elastic modulus and strength parameters) of the cores was measured by using a high-pressure triaxial apparatus. The dual porous media containing micro-fractures were prepared by this apparatus. Combining numerical simulation with experiments, the relationship between mechanical properties and stress sensitivity and the influence of fracture generation on rock stress sensitivity were studied, which can provide the analysis and interpretation for the production process of tight oil reservoir (Chapter 4).
(4) An experimental study was carried out on the micro-seepage mechanism of dynamic fractures. The rate-controlled water pressure was used to induce cracking and expansion of micro-fractures to obtain the critical pressure difference and steady pressure difference of dynamic fractures. A dual pore-fracture network model with dynamic cracking of micro-fractures was established, which can perform the influences of critical pressure difference, displacement pressure, steady pressure difference, etc. The micro-seepage characteristics of the dual porous media with dynamic cracking of micro-fractures had been investigated (Chapter 5).
|刘海娇. 基于孔隙-裂隙双重网络模型对水驱油微观渗流机理的研究[D]. 北京. 中国科学院大学,2018.|
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