连通域标识法在FMI图像溶洞信息定量拾取中的应用

溶蚀孔洞在碳酸盐岩储层中是重要的流体储集空间,研究成像测井(FMI)图像孔洞连通域标记及信息定量拾取很有意义.全井眼微电阻率成像测井(FMI)经数据处理后可得到全井壁高分辨率的彩色图像,经图像灰度化、中值滤波处理后,通过阈值分割得到能够反映井壁溶蚀孔洞特征的二值图像,孔洞表现为黑色暗斑.基于等价对处理的图像连通域标记算法具有快速、不重复标记的优点,利用该算法,可准确地从二值图像中标记溶蚀孔洞连通域,进而可对每个连通域进行目标信息拾取,包括孔洞尺寸、连通域面积、圆度等.利用反映溶蚀孔洞发育程度的面孔率曲线对图像进行分层,在此基础上可拾取每一层段溶蚀孔洞面孔率、分选系数及溶洞密度值的分布等非均质信息,能够定量地评价溶蚀孔洞发育、非均质性强的碳酸盐岩储层,也是FMI图像应用于岩石孔洞结构信息定量表征新的尝试.     

应用最小二乘法求解平面P波在孔洞上的散射

弹性波在孔洞上的散射问题可采用复变函数方法求解,用含有待定系数的"域函数"表示散射波的位移势函数,如何准确地求解该待定系数是获得问题解答的关键。本文根据孔洞边缘的径向和切向应力为零的边界条件用最小二乘法建立求解待定系数的线性方程组,得到有限项系数的近似解。通过圆孔、椭圆孔和方孔的数值算例,分析了P波作用下不同形状孔洞边缘的动应力集中系数的特征,讨论了孔边的径向和切向应力计算误差与待定系数项数的关系。计算结果表明,采用最小二乘法求解散射波的待定系数,能够获得满足一定精度要求的孔附近动应力集中系数的解答。     

各向异性半空间中浅埋孔洞对地表 反平面运动的影响

本文采用复变函数方法研究了稳态水平剪切波(SH波)在各向异性弹性半空间中任意形状孔洞上的散射及其对地面运动的影响.在变换空间中构造出自动满足各向异性半空间水平表面上应力为零的散射波函数,并根据孔洞表面应力为零的边界条件,采用最小二乘法求解散射波函数的系数.用介质的各向异性性质来模拟地质条件,给出了SH波作用下含圆孔、椭圆孔和方孔的各向异性半空间表面位移幅值的数值结果,并分析了介质特性、孔洞的形状、埋深、入射波波数及入射角度等因素对地面运动的影响规律.数值结果表明:介质的各向异性对含有孔洞的半空间表面的地表位移具有显著的影响;沿一定角度的入射波在某一频段内所引起的地表位移幅值比各向同性介质的可能要大,且随着孔洞埋深的增加,地表位移的幅值逐渐减小.      

基于小波变换图像分割技术的电成像测井资料裂缝、孔洞面孔率提取方法

对于裂缝、溶蚀孔洞发育的碳酸盐岩缝洞储层,如何从测井资料中提取裂缝、溶蚀孔洞信息是评价储层有效性的关键问题.为了从电成像测井静态图像上准确地分割出清晰的裂缝、溶蚀孔洞子图像进而提取其参数信息,本文提出了一种基于小波变换模极大值图像分割技术的电成像测井资料缝洞面孔率提取方法.以钮扣电极电导率曲线为对象,先消除井壁凹凸不平导致的地层背景噪声的影响,利用小波变换模极大值图像分割方法得到包含裂缝和溶蚀孔洞目标的子图像,根据子图像提取裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率等信息.本文利用塔里木盆地奥陶系碳酸盐岩地层的电成像测井数据提取了缝洞面孔率参数,还利用同井岩心CT扫描图像计算的平均缝洞面孔率、双侧向电阻率、常规测井资料三孔隙度模型计算的相对连通缝洞孔隙度进行了对比,并进行了试油验证.对比表明,电成像测井裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率与岩心CT扫描图像平均缝洞面孔率、双侧向电阻率、相对连通缝洞孔隙度、试油结果均有较好的一致性.这一方面验证了采用本文方法提取的裂缝-孔洞总面孔率、裂缝面孔率、孔洞面孔率的合理性,另一方面表明所提取参数可用于指示缝洞型碳酸盐岩储层的渗透性和有效性.     

碳酸盐岩储层孔隙度超声波评价数值模拟

孔隙度是地质勘探、储层评价及产能预测的重要基础参数.本文利用理想岩心和对实际岩样图像进行数字图像处理建立数字岩心,在此基础上进行二雏超声波数值模拟计算,开展孔洞型储层孔隙度预测研究.研究表明:wyllie平均时间公式在孔洞型地层中并非完全不适用,其适用性由孔洞尺寸及孔洞密度共同控制;当孔密度为0.08~0.064(个/mm~2)时实测孔隙度-波速关系背离wyllie理论计算值,当孔密度大于0.096(个/mm~2)时实测孔隙度-波速的关系趋近wyllie计算值;定孔隙度时,孔隙密度-品质因数呈Q~(-1)=aln(ρ)+b对数规律变化;定孔隙密度时,孔隙度-品质因数呈φ=aQ~(-1)+b线性规律变化,预测模型的系数直接受到孔隙密度的影响,孔隙密度越大则b值越大.     

孔洞型储层测井饱和度解释方程的确定及应用(英文)

孔洞型储层是国内非均质碳酸盐岩油气藏中最常见的一类重要储层。但关于用测井方法计算这类储层油气饱和度的研究却十分薄弱,多数情况仍沿用传统方法。本文首先从理论上分析了孔洞型储层岩电关系,得出了其岩电关系曲线存在特殊的"平台"现象,通过一系列具有特定孔洞特征的岩心的单因素数值模拟和岩电实验,详细研究了不同孔洞大小、数量及分布对岩电关系的影响。在此基础上,基于饱和度通解方程理论确定了孔洞型储层测井饱和度解释方程的具体形式,从水电相似原理出发推导得出方程参数是与孔洞和基质孔隙的大小分布等孔隙结构有关的物理量。基于此,提出了一种利用核磁测井资料构造核磁毛管压力曲线、求取孔隙结构参数、进而确定方程待定参数的方法。现场应用证明,新方程的饱和度计算结果与取心分析结果符合良好,平均绝对误差为5.8%。。     

P波入射时含圆柱形空腔板弹性波散射与动应力集中

采用波函数展开法给出了板的横截面处孔洞在平面P波入射下动应力集中问题的解。本文使用大圆弧假定法来满足板中的自由表面的边界条件。数值结果表明,上表面和孔洞间的距离与下表面和孔洞间的距离都对结果有影响。如果孔洞半径相对板的厚度很小,解近似等于孔洞全空间解。所给出的解是半解析解。因此能被用来验证诸如BEM,FEM,FDM等数值法。     

应用三重孔隙模型评价火成岩储层

火成岩岩性特殊,储层非均质性非常严重,裂缝、孔洞发育,属于典型的多重孔隙介质储层,定量计算火成岩储层基质和裂缝的孔隙度和饱和度是评价火成岩油气层的关键。由基质、天然裂缝和非连通孔洞组成的储层可以模拟成基质和裂缝的并联导电网络,非连通孔洞和基质／裂缝的组合的串联导电网络。采用密度测井资料求取总孔隙度,用深浅双侧向电阻率计算裂缝孔隙度,采用密闭取心分析的孔隙度作为基质孔隙度。通过建立以基质、天然裂缝和非连通孔洞组成的储层的三重孔隙解释模型,找到适合于火成岩缝洞型复杂储层的饱和度方程。将三重孔隙解释模型应用于松辽盆地北部火成岩储层,计算的含水饱和度平均相对误差由16．85％降低至12．42％,精度明显提高,为火成岩储层评价、储量计算与地质建模提供了定量参数。     

冲击载荷下孔洞附近的动应力集中

本文用微闪系统研究了冲击载荷作用下,半无限弹性平面中五种型式孔洞附近的动应力分布和动应力集中问题。文中分析了弹性波对孔洞的绕射过程,并测定了几种型式孔洞周边的动应力分布和动应力集中系数随时间的变化规律。     

SH波入射时多个半圆形沉积谷地附近浅埋圆形孔洞的动力分析

本文采用辅助函数的思想,利用复变函数和多级坐标的方法给出了SH波入射条件下多个半圆形沉积谷地附近浅埋圆形孔洞动力分析问题的解答。将整个求解区域分割成两部分来处理,区域I为多个半圆形沉积谷地,区域II为浅埋圆形孔洞附近带半圆形凹陷的半无限弹性空间。在区域I和II中分别构造位移解,并在二个区域的“公共边界”上实施位移应力的连续条件,建立求解该问题的无穷代数方程组。最后,本文给出了算例和数值结果,并对其进行了讨论。     

Large-scale floodplain modelling

A two-dimensional horizontal finite element numerical model (RMA-2) was applied to a 24 km river channel-floodplain reach in West Germany. Initial results indicate that finite element schemes may successfully estimate inundation in large-scale floodplain applications. Potentially, the resulting detailed velocity vector distributions and identification of inundation zones throughout storm events could provide an insight into the present day sedimentary environment on the floodplain.     

Uncertainty in sewer sediment deposit modelling: Detailed vs simplified modelling approaches

The paper presents the results of a study in which the uncertainty levels associated with a detailed and a simplified/parsimonious sewer sediment modelling approach have been compared. The detailed approach used an Infoworks CS sewer network model combined with a user developed sediment transport code and the simplified approach used a conceptual sewer flow and quality model. The two approaches have been applied to a single case study sewer network and the simulation results compared. The case study was selected as moderate storm events had occurred during a 2 year rainfall and sewer flow monitoring period. Flooding had been observed and this was thought to be caused by significant solids accumulation in the sewer network. As a result sediment deposit measurements were carried out over a 6 month period. Model simulations were made of this period and predictions obtained of sediment deposit location and depth. The uncertainty analysis of both modelling approaches was carried out using Monte Carlo based computational methods. This was a limitation for the detailed approach with regards to computational time. Use of the simplified model was not constrained by this issue and so a more conventional assessment of the uncertainty was possible. The simplified approach, due to its structure, only provided a temporal estimate of uncertainty at the final section of the catchment. The detailed approach enabled an assessment of uncertainty at an individual pipe scale but only at the end of the simulation period. A comparison of the uncertainty estimations from both methods at the final section of the catchment and the end of the simulation period indicated comparable values of predicted uncertainty. Therefore a complementary use of both approaches would allow reasonably comparable estimations of levels of uncertainty at both a spatial and temporal scale. The use of such modelling approaches may provide a useful decision-making tool for sewer system management.     

Pore-scale imaging and modelling

Pore-scale imaging and modelling – digital core analysis – is becoming a routine service in the oil and gas industry, and has potential applications in contaminant transport and carbon dioxide storage. This paper briefly describes the underlying technology, namely imaging of the pore space of rocks from the nanometre scale upwards, coupled with a suite of different numerical techniques for simulating single and multiphase flow and transport through these images. Three example applications are then described, illustrating the range of scientific problems that can be tackled: dispersion in different rock samples that predicts the anomalous transport behaviour characteristic of highly heterogeneous carbonates; imaging of super-critical carbon dioxide in sandstone to demonstrate the possibility of capillary trapping in geological carbon storage; and the computation of relative permeability for mixed-wet carbonates and implications for oilfield waterflood recovery. The paper concludes by discussing limitations and challenges, including finding representative samples, imaging and simulating flow and transport in pore spaces over many orders of magnitude in size, the determination of wettability, and upscaling to the field scale. We conclude that pore-scale modelling is likely to become more widely applied in the oil industry including assessment of unconventional oil and gas resources. It has the potential to transform our understanding of multiphase flow processes, facilitating more efficient oil and gas recovery, effective contaminant removal and safe carbon dioxide storage.     

One-dimensional modelling of mantle flow

A one-dimensional model of flow between a fixed boundary at the bottom and a moving one on top with no net flow through vertical sections is tested for geophysically interesting mantle viscosity-depth functions. Such a model, although simplistic, may help in answering the question to what depth the return flow extends, at least in the case of moving plates measuring many thousand kilometers across, such as the Pacific plate.It the viscosity in the asthenosphere is less than three orders of magnitude smaller than that of the mantle below, the return flow extends to great depth and the asthenosphere is a zone of concentrated shear. If the viscosity contrast is greater, the return flow is concentrated in the asthenosphere. For a wide range of model parameters typical flow velocities below the asthenosphere are about one-tenth of the plate velocity. The pressure gradient required by the mantle flow may be manifest in gravity trends across moving plates, but no excessive gravity anomalies are required by the model if the absolute viscosity values conform to those inferred from post-glacial rebound data. A thinner and lower-viscosity layer is favored over a thicker and more viscous layer if both fit glacial rebound evidence. The present model may not be applicable if down to the core the viscosity is as low as about 10²¹ N s m^–2 with a free-slip bottom boundary.     

Realistic modelling of shelf-estuary regions

A very high-resolution modelling configuration was created for the estuary of Baía de Todos os Santos – BTS, Brazil (300 to 400 m), and adjacent coastal waters (600 to 1200 m). The adoption of a multi-corner domain approach allowed the variable spatial resolution required to resolve the shelf, the bay and their interactions. Seven years were simulated using realistic oceanic, atmospheric and riverine forcing. Model validation was done against observations showing the model skill to reproduce the thermohaline field, the tidal currents, as well as the variability of the free surface at tidal and sub-tidal time scales. The results provide the first representation of the tidal wave propagation along the bay, in terms of maps of amplitudes, phases and ellipses of the barotropic currents for the main tidal constituents. By analysing the residual currents at different depths, in terms of averages over the simulation period, several prominent structures were identified and named: (i) Salvador eddy (up to 0.2 m s⁻¹); (ii) St Antonio current (up to 0.45 m s⁻¹); (iii) Salvador current (up to 0.5 m s⁻¹); (iv) Itaparica eddy (up to 0.2 m s⁻¹); (v) Ilha dos Frades southern eddy (up to 0.1 m s⁻¹); and (vi) Ilha dos Frades northern eddy (up to 0.2 m s⁻¹). The model set-up proved to be highly efficient and robust simulating the BTS shelf-estuary region and such an approach may be suitable to other estuarine systems.

     

Electrochemical modelling of self-potential anomalies

An electrochemical model is proposed, which considers the redox conditions and the electrode kinetics at the mineral surface. Advanced modelling of self-potential (SP) anomalies over ore deposits takes into account the course of the redox potential distribution with depth and the oxidation-reduction processes acting at the mineral-electrolyte interface. The application of this model to a SP anomaly in the vicinity of the German Continental Deep Drilling Program (KTB) can explain the surface and borehole data and gives an estimation of the prevailing thermodynamical conditions in the ground.Exclusively, this paper deals with SP anomalies, which are associated with high conductive graphitic layers. It can be concluded that SP-anomalies give an important hint to electronical conducting structures in the earth's crust.