Yongfei Li

The Effect of the Absorbed Fluid Layer on Flow in a Capillary Tube

There exists an absorbed fluid layer (AFL) on solid surface for the interaction between fluid molecules and the solid surface. A simple capillary model considering absorbed fluid layer is developed to investigate the influence of AFL on the dynamic behavior of flow in micron scale capillary tubes. An empirical formula for calculating the thickness of AFL is presented. The correlation between the effective permeability, the driving pressure gradient and the thickness of AFL is studied. On this basis, the flow mechanism in low-permeability reservoirs is researched preliminarily. The results reveal that the thickness of AFL is not fixed, but a function of driving pressure gradient, which causes a modification of effective permeability of single tube in accordance with driving pressure gradient and the formation of threshold pressure gradient.

Study on Stability and Treatment of Surfactant/Polymer Flooding Waste Water

Surfactant is mainly responsible for the stability of oil droplets in surfactant/polymer flooding waste water compared with polymer, decreasing oil-water interfacial tension, and zeta potential on the surface of the oil droplets. Flocculation and demulsification were conducted to remove the stable oil droplets. Demulsifier reverse phase demulsifer-E (RPDE) together with flocculant cationic polyacrylamide is effective in accelerating the coalescence of small oil droplets in surfactant/polymer flooding waste water due to synergistic effect of demulsification and flocculation.

Synthesis and evaluation of properties of N,N-bis(perfluorooctyl)imine acetate sodium as a gas-wetting alteration agent

The wettability of a rock’s surface is a vital factor for gas flow and fracturing fluid backflow. As a result of this, novel and effective gas wetting alteration agents are required. In this work, a gas-wetting alteration agent, N,N-bis(perfluorooctyl)imine acetate sodium, was synthesized and characterized by different methods. The wettability of a rock’s surface was evaluated by contact angle and imbibition measurements, the Owens two-liquid method and glass capillary tube rise testing. The results showed that after treatment with 0.5 wt% N,N-bis(perfluorooctyl)imine acetate sodium the contact angles of water and n-hexadecane on the surface of the rock increased from 36° and 0° to 140° and 119°, respectively. The surface free energy rapidly reduced from primeval 72 mN m−1 to 3.4 mN m−1 after treatment with 0.3 wt% N,N-bis(perfluorooctyl)imine acetate sodium. These values agreed with the imbibition measurements and the results of the glass capillary tube rise testing. Moreover, analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that the roughness of the rock surface significantly increased. The above results fully proved that the wettability of the rock surface is altered from its original water-wetting or oil-wetting to gas-wetting. Furthermore, thermal analysis demonstrated that the gas-wetting alteration agent has good thermal stability, which indicates its great potential to be used as a gas-wetting alteration agent for unconventional gas reservoirs under high temperature conditions.

The effect of N-ethyl-N-hydroxyethyl perfluorooctanoamide on wettability alteration of shale reservoir

The wettability of the formation is critical for the flow back of the fracturing fluid and can further affect the gas production. So it is very necessary to study the wettability of shale reservoir. Here, a novel fluorocarbon surfactant, N-ethyl-N-hydroxyethyl perfluorooctanoamide, was synthesized and characterized by different methods. the contact angles of water and n-decane on the shale increased from 36° and 0° to 121° and 105°, respectively, after treated by N-ethyl-N-hydroxyethyl perfluorooctanoamide (0.5 wt.%). The surface free energy reduced from 72 mN/m to 7.4 mN/m. The results agreed with that of imbibition and capillary tube rise test. Additionally, the analysis of scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) showed that the roughness of shale surface remarkably increased. These results fully proved that the shale wettability is changed to super gas-wetting. Besides, the thermal analysis revealed that the novel fluorocarbon surfactant has good thermal stability. This indicates that it can be better applied to reservoir modifications at higher temperatures.

The effect of fluorocarbon surfactant on the gas-wetting alteration of reservoir

ABSTRACT Reservoir wettability plays a vital role in the production of shale gas. In this work, two fluorocarbon surfactants were synthesized and characterized. The wettability of shale surface was evaluated by different method. The results showed that the contact angles of water and oil increased significantly after treatment. The surface free energy rapidly reduced to 10.3 mN/m and 5.9 mN/m, respectively. The roughness of the shale surface remarkably increased. These results confirmed that the shale wettability is altered from liquid-wetting to gas-wetting. Besides, the thermal analysis exhibited that they have good thermal stability before 173°C and 201°C, respectively.

A Productivity Prediction Model for the Gravel-packed Horizontal Well

By rigorously coupling reservoir seepage and various mass flow in wellbore, the authors first present a new model to predict the productivity of a gravel-packed horizontal well. The fourth-order Runge-Kutta method is employed to solve the model, and it can be used to calculate pressure, flow rate distribution along the wellbore, and productivity. Compared with the existing mathematical models and field data, the new model has two advantages: (a) it is more accurate than other models, and (b) it is very easy to use.

Orthogonal Experiment Design of Numerical Simulation for Underground Oil Storage Caverns

Abstract An appropriate scheme is very important to the design of underground oil storage caverns. The layout and direction of caverns, the shape and dimension of section, the construction sequence, and excavation methods will have different effects on the optimum design and long-term stabilities of storage caverns. Considering these actual characters in the numerical simulation experiment for the design of underground oil storage caverns, the orthogonal experiment design is applied to the optimizing design of the caverns, and the optimum layout and directions of the caverns, the appropriate dimensions of the section, the optimum horizontal spacing between caverns, and construction sequence have been obtained. The corresponding calculation methods on the experiment parameters have been established.