CO2geological sequestration modelling and injection induced fracturing analysis of the caprock

In geological sequestration, CO2is injected under high pressure into deep underground rock formations, including deep saline aquifers. This paper presents the invading supercritical CO2-brine two-phase numerical model to describe CO2flow and transport processes in deep saline aquifers. The effects of anisotropy and different kinds of heterogeneity like horizontal and vertical layers and also existence of barriers between layers on the CO2flow and transport in a saturated porous media with brine are investigated using the presented two-phase model. Following to simulation results, it can be obtained that the permeability of the rock formations and the permeability anisotropy should be considered as the most important parameters in CO2flow and transport processes and its distribution in the rock formations. Furthermore, the capillary pressure on the buoyancy-driven flow of CO2is analyzed, and the XFEM is adopted to simulate the injection induced fracturing process of the naturally fractured caprock. © 2013 Taylor & Francis Group

Alternative constitutive relation for momentum transport of extended Navier-Stokes equations*

The classical Navier-Stokes equation (NSE) is the fundamental partial differential equation that describes the flow of fluids, but in certain cases, like high local density and temperature gradient, it is inconsistent with the experimental results. Some extended Navier-Stokes equations with diffusion terms taken into consideration have been proposed. However, a consensus conclusion on the specific expression of the additional diffusion term has not been reached in the academic circle. The models adopt the form of the generalized Newtonian constitutive relation by substituting the convection velocity with a new term, or by using some analogy. In this study, a new constitutive relation for momentum transport and a momentum balance equation are obtained based on the molecular kinetic theory. The new constitutive relation preserves the symmetry of the deviation stress, and the momentum balance equation satisfies Galilean invariance. The results show that for Poiseuille flow in a circular micro-tube, self-diffusion in micro-flow needs considering even if the local density gradient is very low

Influence of Spacer Chain Length on the Rheological Properties of Gemini Surfactant

用毛细管振荡剪切流动法研究了联接基团为聚亚甲基链的阳离子 Gemini表面活性剂的流变性质。实验结果表明 ,无论是普通单链单头基或 Gemini表面活性剂 ,其流变性质主要由胶团的大小和形状所决定 ;随着联接基团长度的增加 ,胶团的轴比率变小 ,导致流动阻力减小 ,粘度降低。此外对于球形和棒状胶团溶液 ,其流变性质主要以粘性为主 ,弹性可忽略不计。在低剪切速率下 ,溶液属于牛顿型流体 ;而在高剪切速率下 ,则表现出准塑性流体性质。By the means of oscillatory shear flow in the capillary, rheological experiments are carried out on aqueous solutions of the cationic Gemini surfactant as a function of suffactant concentration. The results show that the rheological property is mostly determined by the size and shape of micelles. The axial ratio of micelles decreases with increasing the length of spacer chain, so the viscosity of solution decreases.国家自然科学基金资助项目 (2 99730 33

Micellar Growth of Quaternary Ammonium Gemini Surfactant in Aqueous Solutions Using Dynamic Light Scattering

用动态光散射技术在 10～ 70℃温度范围内 ,通过测定胶团的平均流体力学半径随温度、盐浓度和联接基团长度的变化情况 ,研究联接基团为聚亚甲基链的阳离子季铵盐Gemini表面活性剂胶团在无机盐介质中的长大规律 .实验结果表明 ,增加盐量、降低温度和减小联接基团的长度均使平均流体力学半径变大 ,Gemini表面活性剂胶团长大时是由球状转变为棒状 .从实验测定的平流体力学半径求算了支配球 -棒转变的平衡常数及热力学函数值 ,并用NNLS (non negativelyconstrainedleastsquare)算法对胶团的粒径分布情况进行了分析 .此外 ,对具有短联接基团的Gemini表面活性剂胶团长大所具有的独特性质进行了讨论 .The micellar growth of quaternary ammonium Gemini surfactants containing methylene group spacer (referred to as C 12-s-C 12, 2Br) in inorganic salt (NaBr) media was investigated by using dynamic light scattering. The size of micelles increases with increasing salt concentration or decreasing temperature or decreasing the length of spacer chain. The enlarged micelles have a shape of prolate ellipsoid or rod. Based on these mean hydrodynamic radius (R h) measurements, values of the thermodynamic parameter K governing the sphere to rod transition were determined. Numerical values of enthalpy and entropy change for this transition were deduced from the linear plot of ln K vs. 1/T. The novel micellar growth of C 12-2-C 12, 2Br was discussed. The distribution of micelle size was analyzed by using non-negatively constrained least square (NNLS) algorithm.国家自然科学基金 (No .2 99730 33)资助项

Investigation on the Interaction between Quaternary Ammonium Surfactants and Lecithin Vesicles

采用动态光散射、ζ电势等方法研究了季铵盐二聚表面活性剂(C12-8-C12?2Br)和十二烷基三甲基溴化铵(DTAB)在卵磷脂囊泡中的增溶作用.C12-8-C12?2Br使囊泡粒径增大,促进脂双层向胶团的转变,过程明显分为三个阶段;而DTAB与囊泡的作用则相对缓和,72h内未见明显变化.此外,用亲水头基总体积的大小,讨论了这两种表面活性剂在脂质体中的吸附行为,并对实验现象加以解释说明.The solubilization process of quaternary ammonium surfactants within lecithin vesicles has been studied by means of optical density monitoring, dynamic light scattering (DLS) and ζ-potential. To C12-8-C12?2Br-liposome system, the vesicle-to-micelle structure transition occurred within 6 h, and could be described by a simple three-stage model. While the DTAB-liposome system remained vesicle state even af- ter 48 h. The size of total volume of hydrophilic head group (Vhead) as the main influencing factor was investigated.国家自然科学基金(No.29973033)资助项目

不同卸载速率下受载煤体裂隙结构演化机制

针对受载煤体卸压过程裂隙发育数据难以捕捉的现状,设计了受载煤体伪三轴瓦斯渗流实验,完成了受载煤体加载和卸载过程的应力-应变-渗透率动态监测。同时基于能量守恒定理,开展了卸载过程中不同卸载速率下的能量分配比较,阐释了卸载速率对裂隙发育和渗透率变化的控制作用,并通过煤样裂隙监测数据对比予以验证。研究结果显示,卸载过程中的煤体裂隙结构受卸载速率影响,围压卸载速率越高,I类和II类裂隙越发育(所占比率增高),I类裂隙数量较原始数量增幅甚至超过1倍,II类裂隙数量提高74.13%;在卸载过程中渗透率曲线整体可分为3段:线性段、抛物线段和稳定段,而决定其3段曲线分布的关键因素是煤体弹性模量大小、加载强度和卸载速率;随着卸载速率的提高,煤体渗透率加大,线性段斜率和抛物线段曲率半径逐步增加,线性段斜率由0.054 8逐步升高至0.091 9,0.138 8和0.216 4,抛物线曲率半径逐步增大,顶点曲率半径分别达到1.232,1.334,1.863和2.014,渗透率稳定的应力临界点不断减小,由15.26 MPa降低至14.08,13.14和10.88 MPa;煤体渗透率的变化可以通过裂隙长度增量进行量化表征,相同实验条件下,渗透率增量与裂隙长度增量之间呈线性关系;统计数据显示,围压卸载速率越高,弹性能转化率越低,裂隙发育能耗越高,高速卸载(加卸比1∶8)可使煤体破裂能耗超过80%,而低速卸载(加卸比1∶1)的裂隙能耗仅有25.62%;比较研究发现,高速卸载过程中煤体能量释放的主体引发原有裂隙扩展,而不是导致新裂隙的萌生,裂隙发育能耗与卸载速率之间呈对数关系

Micellar growth of quaternary ammonium Gemini surfactant in aqueous solutions using dynamic light scattering

The micellar growth of quaternary ammonium Gemini surfactants containing methylene group spacer (referred to as C-12-s-C-12, 2Br) in inorganic salt (NaBr) media was investigated by using dynamic light scattering. The size of micelles increases with increasing salt concentration or decreasing temperature or decreasing the length of spacer chain. The enlarged micelles have a shape of prolate ellipsoid or rod. Based on these mean hydrodynamic radius ((R) over bar (h)) measurements, values of the thermodynamic parameter K governing the sphere to rod transition were determined. Numerical values of enthalpy and entropy change for this transition were deduced from the linear plot of ln K vs. 1/T. The novel micellar growth Of C-12-2-C-12, 2Br was discussed. The distribution of micelle size was analyzed by using non-negatively constrained least square (NNLS) algorithm

Investigation on the interaction between quaternary ammonium surfactants and lecithin vesicles

The solubilization process of quaternary ammonium surfactants within lecithin vesicles has been studied by means of optical density monitoring, dynamic light scattering (DLS) and zeta-potential. To C-12-8-C(12)center dot 2Br-liposome system, the vesicle-to-micelle structure transition occurred within 6 h, and could be described by a simple three-stage model. While the DTAB-liposome system remained vesicle state even after 48 h. The size of total volume of hydrophilic head group (V-head) as the main influencing factor was investigated

Flowing material balance method with adsorbed phase volumes for unconventional gas reservoirs

This paper presents an improved flowing material balance method for unconventional gas reservoirs. The flowing material balance method is widely used to estimate geological reserves. However, in the case of the unconventional gas reservoirs, such as coalbed methane reservoirs and shale gas reservoirs, the conventional method is inapplicable due to the gas adsorption on the organic pore surface. In this study, a material balance equation considering adsorption phase volume is presented and a new total compressibility is defined. A pseudo-gas reservoir is simulated and the results were compared with the existing formulations. The results show that the proposed formulation can accurately get the geological reserves of adsorbed gas reservoirs. Furthermore, the results also show that the volume of the adsorbed phase has a significant influence on the analysis, and it can only be ignored when the Langmuir volume is negligible

Investigation of Analysis Methods for Pulse Decay Tests Considering Gas Adsorption

The pulse decay test is the main method employed to determine permeability for tight rocks, and is widely used. The testing gas can be strongly adsorbed on the pore surface of unconventional reservoir cores, such as shale and coal rock. However, gas adsorption has not been well considered in analysis pulse decay tests. In this study, the conventional flow model of adsorbed gas in porous media was modified by considering the volume of the adsorbed phase. Then, pulse decay tests of equilibrium sorption, unsteady state and pseudo-steady-state non-equilibrium sorption models, were analyzed by simulations. For equilibrium sorption, it is found that the Cui-correction method is excessive when the adsorbed phase volume is considered. This method is good at very low pressure, and is worse than the non-correction method at high pressure. When the testing pressure and Langmuir volume are large and the vessel volumes are small, a non-negligible error exists when using the Cui-correction method. If the vessel volumes are very large, gas adsorption can be ignored. For non-equilibrium sorption, the pulse decay characteristics of unsteady state and pseudo-steady-state non-equilibrium sorption models are similar to those of unsteady state and pseudo-steady-state dual-porosity models, respectively. When the upstream and downstream pressures become equal, they continue to decay until all of the pressures reach equilibrium. The Langmuir volume and pressure, the testing pressure and the porosity, affect the pseudo-storativity ratio and the pseudo-interporosity flow coefficient. Their impacts on non-equilibrium sorption models are similar to those of the storativity ratio and the interporosity flow coefficient in dual-porosity models. Like dual-porosity models, the pseudo-pressure derivative can be used to identify equilibrium and non-equilibrium sorption models at the early stage, and also the unsteady state and pseudo-steady-state non-equilibrium sorption models at the late stage. To identify models using the pseudo-pressure derivative at the early stage, the suitable vessel volumes should be chosen according to the core adsorption property, porosity and the testing pressure. Finally, experimental data are analyzed using the method proposed in this study, and the results are sufficient