基于等效Thomsen参数的P-SV波AVO属性研究

在等效Thomsen各向异性参数的P-SV波反射系数近似公式基础上研究了反射系数的多种AVO(振幅随炮检距变化)属性特征,针对不同的属性特征构建了多属性AVO交绘图;并利用反射系数公式对三类含气砂岩AVO的特征进行分析.结果表明P-SV波反射系数公式可以有效的区分第三类含气砂岩;岩石的孔隙度、流体饱和度等信息是影响地震波AVO的重要因素.利用Gassmann方程进行了对上层为HTI介质,下层为孔隙储层的介质模型进行了流体替换计算,分析了孔隙度、含气饱和度和各向异性参数变化对地层AVO的影响.     

Numerical simulation of seismic wave propagation in complex media by convolutional differentiator

We apply the forward modeling algorithm constituted by the convolutional Forsyte polynomial differentiator pro-posed by former worker to seismic wave simulation of complex heterogeneous media and compare the efficiency and accuracy between this method and other seismic simulation methods such as finite difference and pseudospec-tral method. Numerical experiments demonstrate that the algorithm constituted by convolutional Forsyte polyno-mial differentiator has high efficiency and accuracy and needs less computational resources, so it is a numerical modeling method with much potential.     

Nonequilibrium effects in models of three-phase flow in porous media

In this paper we extend to three-phase flow the nonequilibrium formalism proposed by Barenblatt and co-workers for two-phase porous media flow. The underlying idea is to include nonequilibrium effects by introducing a pair of effective water and gas saturations, which are linked to the actual saturations by a local evolution equation. We illustrate and analyze how nonequilibrium effects lead to qualitative and quantitative differences in the solution of the three-phase flow equations.     

Unsaturated water flow across soil aggregate contacts

Unsaturated water flow through soil aggregates is controlled by the contacts between aggregates. The contacts are highly conductive when wet and become bottle-necks for flow when drained. We postulate that the hydraulic conductivity of the contacts is in first place determined by the water-filled contact area. The objective of this study was to measure and model the water-filled contact area and to relate it to the conductivity of a series of aggregates. We performed microscopic tomography of an aggregate pair equilibrated at different water potentials. By means of image analysis and a morphological pore network model, the water-filled contact area was calculated. We found that the aggregate surface is rough and the contact region contains macropores which are rapidly drained. As a consequence the water-filled contact area dramatically decreases as the water potential is diminished. We modeled this process by describing the aggregates as spheres covered by much smaller spheres representing the roughness. The water-filled contact was analytically calculated from this model. Knowing the water-filled contact area we up-scale the hydraulic conductivity of a series of aggregates. This is calculated as the harmonic mean of the contact and aggregate conductivities. The contact conductivity is calculated from the water-filled contact area. Near saturation the conductivity of a series of aggregates is close to the conductivity of a single aggregate, and, when further drained, it rapidly decreases as the water-filled contact area. The model matches the experimental data well.     

Application of implicit sub-time stepping to simulate flow and transport in fractured porous media

In general, the accuracy of numerical simulations is determined by spatial and temporal discretization levels. In fractured porous media, the time step size is a key factor in controlling the solution accuracy for a given spatial discretization. If the time step size is restricted by the relatively rapid responses in the fracture domain to maintain an acceptable level of accuracy in the entire simulation domain, the matrix tends to be temporally over-discretized. Implicit sub-time stepping applies smaller sub-time steps only to the sub-domain where the accuracy requirements are less tolerant and is most suitable for problems where the response is high in only a small portion of the domain, such as within and near the fractures in fractured porous media. It is demonstrated with illustrative examples that implicit sub-time stepping can significantly improve the simulation efficiency with minimal loss in accuracy when simulating flow and transport in fractured porous media. The methodology is successfully applied to density-dependent flow and transport simulations in a Canadian Shield environment, where the flow and transport is dominated by discrete, highly conductive fracture zones.     

Numerical modeling of two-phase flow in heterogeneous permeable media with different capillarity pressures

Contrast in capillary pressure of heterogeneous permeable media can have a significant effect on the flow path in two-phase immiscible flow. Very little work has appeared on the subject of capillary heterogeneity despite the fact that in certain cases it may be as important as permeability heterogeneity. The discontinuity in saturation as a result of capillary continuity, and in some cases capillary discontinuity may arise from contrast in capillary pressure functions in heterogeneous permeable media leading to complications in numerical modeling. There are also other challenges for accurate numerical modeling due to distorted unstructured grids because of the grid orientation and numerical dispersion effects. Limited attempts have been made in the literature to assess the accuracy of fluid flow modeling in heterogeneous permeable media with capillarity heterogeneity. The basic mixed finite element (MFE) framework is a superior method for accurate flux calculation in heterogeneous media in comparison to the conventional finite difference and finite volume approaches. However, a deficiency in the MFE from the direct use of fractional flow formulation has been recognized lately in application to flow in permeable media with capillary heterogeneity. In this work, we propose a new consistent formulation in 3D in which the total velocity is expressed in terms of the wetting-phase potential gradient and the capillary potential gradient. In our formulation, the coefficient of the wetting potential gradient is in terms of the total mobility which is smoother than the wetting mobility. We combine the MFE and discontinuous Galerkin (DG) methods to solve the pressure equation and the saturation equation, respectively. Our numerical model is verified with 1D analytical solutions in homogeneous and heterogeneous media. We also present 2D examples to demonstrate the significance of capillary heterogeneity in flow, and a 3D example to demonstrate the negligible effect of distorted meshes on the numerical solution in our proposed algorithm.     

基于随机介质模型的储层非均质性分析

本文利用随机介质模型对复杂岩性储层进行了非均质性描述.利用模型特征量即非均质纵横比、纵向谱指数、横向谱指数以及扰动标准差等来模拟不同的随机介质.在前人工作的基础上,由某油气田的两口井资料估计储层非均质性能谱,从能谱曲线上提取储层纵向大小尺度非均质谱指数.通过将二维随机介质模拟的合成井记录互相关系数与实际井记录互相关系数进行分析比较,分别得到大小尺度非均质情况下最佳拟合时的横向谱指数和非均质性纵横比.以上求得的各种特征量从不同角度定量分析了储层非均质性的纵横向变化,为储层横向预测提供了依据.     

Numerical experiments for the conductive properties of saturated rock

The reservoir evaluation as a key technology in oil exploration and production is based on the electrical transport property (ETP) of saturated rock that is described in a mathematical form with Arhcie’s equa-tion. But there have been increasing cases observed in many researches indicating that the ETP is non-Archie especially for the complex reservoir with low porosity and permeability. In this paper,the numerical experiments based on the Lattice Boltzmann method (LBM) have been employed to study the effect of porous structure and fluids on the ETP for revealing the nature of non-Archie phenomenon in micro-scale. The results of numerical experiments have proved that the saturation exponent n is a function of water saturation and porosity instead of being a constant in Archie’s equation. And then,a new formula has been developed for the EPT through combining the result of numerical simulation with that of laboratory measurements. The calculations from the new formula show very good agreement with laboratory measurements to demonstrate the efficiency of the new formula over the conventional methods in non-Archie rock.     

Calculation of reflection and transmission coefficients for qP waves incident on a planar interface between isotropic and triclinic media

In the paper by Chattopadhyay and Rajneesh (2006, “Reflection and refraction of waves at the interface of an isotropic medium over a highly anisotropic medium’, Acta Geophysica, vol. 54, no. 3, pp. 239–249), the authors proposed a process to calculate R/T (reflection and transmission) coefficients at the interface between isotropic and triclinic half-spaces, with incident qP waves in triclinic media. Unfortunately, besides several misprints, the authors made a fatal assumption that there is no transmitted SH wave generated in isotropic media, which led the successive analytical derivations and numerical calculations thoroughly wrong. In this paper, the errors are analyzed at length and corrections are given. Then an alternative approach to solve the problem is proposed and numerical results are shown and discussed.     

流体饱和两相多孔介质动力反应计算分析

基于流体饱和两相多孔介质的弹性波动方程组,运用显式逐步积分格式与局部透射人工边界相结合的时域显式有限元方法对该波动方程组进行求解,对两相介质在输入地震波作用下的弹性动力反应进行计算和分析;对在是否考虑孔隙流体渗流的两种情况下计算得到的两相介质弹性动力反应结果的差异进行对比研究,从而揭示孔隙流体渗流对两相介质动力反应性质的影响。计算结果表明：两相介质弹性动力反应时程的波形与入射地震波的波形相同,且弹性动力反应的峰值出现的时刻对应于入射地震波的峰值出现的时刻;孔隙流体的渗流将对两相介质的弹性动力反应性质产生显著的影响。数值计算同时表明,时域显式有限元方法是进行流体饱和两相多孔介质弹性动力反应计算分析的一种有效的方法。