Research advances,geological implication and application in Ordos Basin of the “pore-size controlled precipitation” in diagenesis of carbonate rock reservoir

Based on the discovery of pore-size controlled mineral precipitation and cementation heterogeneity in carbonate rock reservoirs,the state of art and the geological implications are summarized,referring to the fluid-rock interaction and chemical hydrodynamics in porous media. (1)The pore-size controlled precipitation phenomenon is common in geological environments,as shown by the heterogeneous cementation and eventual features that the large pores are filled while small pores can be preserved. Related studies are mainly divided into three aspects,including pore structure observations at different scales,numerical simulation of fluid-rock interaction and mineral precipitation experiment. (2)The kinetic models related to surface chemistry can be used to explain the heterogeneous precipitation affected by pore-size distribution. The larger interfacial tension and mineral crystal curvature in the micropores result in the much higher effective solubility.Thus the fluids in micropores can maintain a higher supersaturation with no minerals precipitation. (3)The pore-size controlled precipitation leads to the selective preservation of micropores. It means that the much larger pores tend to be cement-filled while the smaller pores are preserved in the case of coexistence of pores at different scales. The impacts of cementation types on the overall permeability of rock are different. The pore-size controlled precipitation phenomenon is also worthy of attention in the research of geothermal development and geologic sequestration of carbon dioxide. In the last part, based on the heterogeneous cementation and porosity distribution of the Majiagou Formation in the Ordos Basin,we study the impacts of diagenetic fluids properties,origin and cementation patterns on the evolution of pore structure and high-quality reservoir distribution.The discovery and emphasis of pore-size controlled precipitation is of great theoretical significance to our understanding of the complex fluid-rock interaction process,which provides a new perspective for reservoir diagenesis and pore preservation.     

碳酸盐岩储集层成岩作用中“孔隙尺寸控制沉淀”研究进展、地质意义及鄂尔多斯盆地实例*

基于碳酸盐岩储集层成岩作用中受孔隙尺寸控制的矿物沉淀和胶结非均质特征的发现与思考,结合当今国内外有关多孔介质中流体—岩石相互作用及化学流体动力学研究进展的调研,对相关研究进展及其地质意义进行了简单的梳理和归纳。(1)地质环境中“孔隙尺寸控制沉淀”现象广泛存在,表现为储集层孔隙的胶结非均质性及其最终形成的“大孔充填而小孔保存”特征。现今研究主要从不同尺度孔隙结构观察、流体—孔隙介质相互作用的数值模拟、矿物沉淀实验3个方面开展。(2)受孔隙尺寸控制的非均质沉淀特征可以利用与表面化学相关的动力学模型进行解释,即微孔隙中更大的界面张力和矿物晶体曲率导致矿物的有效溶解度更高,因而更容易保持过饱和状态而不发生沉淀。(3)“孔隙尺寸控制沉淀”现象可使油气储集层发生微孔的选择性保存,在不同尺度孔隙共生的情况下,较大孔隙更倾向于被胶结充填而小孔则更易于被保存,不同的胶结模式对岩石整体渗透率的影响略有不同;该现象在地热储集层开发和二氧化碳地质封存研究中也值得重视。最后,结合鄂尔多斯盆地马家沟组碳酸盐岩储集层的非均质胶结特征和孔隙分布,分析总结成岩流体性质、来源及胶结模式差异对孔隙结构演化和优质储集层分布的影响。“孔隙尺寸控制沉淀”现象的发现和重视对于理解流体—岩石复杂作用过程具有重要理论意义,也为储集层成岩作用和孔隙保存研究提供了新的视点和思考角度。     

The mechanics of hydrothermal systems: II. Fluid mixing and chemical reactions

In the accompanying paper, Part I, hydrothermal mineralising systems are considered as open chemical reactors that operate far from equilibrium to develop an exothermal alteration system with veining and brecciation, followed by competition between endothermic mineralisation and exothermic mineral reactions. In this sequel paper, we examine the interplay of these processes with fluid transport and the impact upon mineral deposition. Chemical reaction and flow in porous media admit two distinct mechanisms which result in significantly accelerated mixing. First, gradients in physical parameters such as chemical potential, fluid density and surface tension generate flow instabilities which form fluid/chemical mixing machines that propagate with the reaction front. Second, so-called chaotic advection, a behaviour in which fluid particles follow chaotic trajectories, arises inherently from Stokes flow in open porous networks as a result of the complexity of the pore geometry. For pore length-scales greater than ~ 1 mm, these mechanisms significantly enhance mixing and hence metal/sulphide deposition. Furthermore, chaotic advection can also alter qualitative characteristics such as stability or speciation of non-equilibrium chemical reactions, with significant implications for enhanced mineralisation rates. Such interactions between chemical reaction and fluid advection generate mineral deposits with multifractal spatial signatures similar to those observed in the field. Such multifractal signatures render the spatial distributions non-ergodic, a fact which process based geostatistics must take into account.     

基于扫描电镜和CT成像技术的碳酸盐岩溶蚀作用微观结构和变化规律研究

为研究溶蚀作用下碳酸盐岩孔隙的演变规律及控制作用,文章选取三峡地区4种类型碳酸盐岩开展溶蚀实验。同时结合扫描电镜、CT成像对实验前后岩石的溶蚀特征及孔隙结构进行测试。结果表明:溶蚀总发生在低晶格能的矿物处且沿矿物晶体的菱形解理面以及薄弱部位发育,表现为对矿物和孔隙等结构的选择性溶解;碳酸盐岩的孔隙度对溶蚀过程影响较小,岩石的孔径大小是影响碳酸盐岩溶蚀速率的重要因素;小孔径岩石的溶蚀多在样品表面发育小型溶孔,大孔径岩石的溶蚀主要发生在孔隙隙壁且有向岩石内部溶蚀的痕迹;经溶蚀改造,孔喉半径和连通性均呈现出增长趋势。本研究对碳酸盐岩差异性岩溶作用机理及岩溶发育规律的认识有一定指导意义。      

离散介质中地震波传播的本构问题

实际地球介质是相当复杂的.基于均匀的、连续介质模型建立的弹性波动理论可能导致对地球结构地震响应的不当解释, 有时可能是错误解释.由于没有更接近实际地球介质模型的波动理论, 许多有用的地震信息因得不到合理解释, 被作为噪音处理了.从等效介质角度来看, 储层介质可以划分为弹性区、粘性区、空白区(空白区是由孔隙、裂隙、结构面产生的介质性质弱化区) 组成的离散介质.在局部平均思想的指导下, 利用区间内聚定理建立起离散(储层) 介质的本构关系, 为建立更接近实际地球介质模型的波动理论提供了力学基础.      

NMR relaxation measurements of biofouling in model and geological porous media

Recently 2D nuclear magnetic resonance (NMR) relaxation techniques have been able to access changes in pore structures through surface and diffusion based relaxation measurements. This research investigates the applicability of these methods for measuring pore and surface changes due to biofilm growth in various model porous systems and natural geological media. Model bead packs of various construction containing 100 μm borosilicate and soda lime glass beads were used to demonstrate how changes in the measured relaxation rates can be used to non-invasively verify and quantify biofilm growth in porous media. However significant challenges are shown to arise when trying to implement the same techniques to verify biofilm growth in a natural geological media.     

Pore Structure Heterogeneity of the Xiamaling Formation Shale Gas Reservoir in the Yanshan Area of China: Evaluation of Geological Controlling Factors

Micro-heterogeneity is an integral parameter of the pore structure of shale gas reservoir and it forms an essential basis for setting and adjusting development parameters. In this study, scanning electron microscopy, high-pressure mercury intrusion and low-temperature nitrogen adsorption experiments were used to qualitatively and quantitatively characterize the pore structure of black shale from the third member of the Xiamaling Formation in the Yanshan area. The pore heterogeneity was studied using fractal theory, and the controlling factors of pore development and heterogeneity were evaluated in combination with geochemical parameters, mineral composition, and geological evolution history. The results show that the pore structure of the reservoir was intricate and complicated. Moreover, various types of micro-nano scale pores such as dissolution pores, intergranular pores, interlayer pores, and micro-cracks are well developed in member 3 of the Xiamaling Formation. The average porosity was found to be 6.30%, and the mean value of the average pore size was 4.78 nm. Micropores and transition pores provided most of the storage space. Pore development was significantly affected by the region and was mainly related to the total organic carbon content, vitrinite reflectance and mineral composition. The fractal dimension, which characterizes the heterogeneity, is 2.66 on average, indicating that the pore structure is highly heterogeneous. Fractal dimension is positively correlated with maturity and clay mineral content, while it is negatively correlated with brittle mineral content and average pore size. These results indicate that pore heterogeneity is closely related to thermal history and material composition. Combined with the geological background of this area, it was found that the pore heterogeneity was mainly controlled by the Jurassic magmatism. The more intense the magma intrusion, the stronger the pore heterogeneity. The pore structure and its heterogeneity characteristics present today are a general reflection of the superimposed geological processes of sedimentary-diagenetic-late transformation. The influence of magmatic intrusion on the reservoir is the main geological factor that should be considered for detailed evaluation of the Xiamaling Formation shale gas reservoir in the Yanshan area.     

珊瑚砂三维孔隙微观特性研究

孔隙是多孔介质内渗流的发生场所,与介质渗透性存在必然的联系。珊瑚砂因其特殊的物质来源和形成过程,较陆源砂具有截然不同的孔隙特性。通过一系列微观研究手段,从本质上揭示了珊瑚砂特殊孔隙性质的原因。研究发现,从孔隙形状、孔喉尺寸和整体连通性3个角度描述孔隙性质较为合理。其中,孔隙形状用形状因子度量,孔喉尺寸包括孔隙半径和喉道半径,珊瑚砂多孔介质整体连通性利用配位数进行描述。而影响孔隙形状、孔喉尺寸和整体连通性的主导因素包括颗粒形状和颗粒表面粗糙度两方面。其中颗粒形状主要影响孔隙形状、喉道尺寸、孔喉尺寸离散性和介质内部连通性的均匀分布情况。颗粒表面粗糙度主要影响孔隙形状、孔隙形状离散性、孔隙尺寸和介质整体连通性。     

鄂尔多斯盆地延长探区延长组页岩气储层孔隙结构特征

为了评价陆相页岩气储层的储集空间和储气能力,以鄂尔多斯盆地延长探区上三叠统延长组长7段、长9段页岩为研究对象,运用电子扫描显微镜、高压压汞、低温CO2和N2气体吸附等实验方法,对陆相页岩气储层孔隙类型特征、孔隙结构及其影响因素进行研究。结果表明：(1)延长探区上三叠统延长组陆相页岩发育多种类型微观孔隙,以粒间孔和粒内孔为主,少量晶间孔和溶蚀孔,有机质孔发育较少,为陆相页岩气赋存提供了储集空间;(2)延长组页岩中介孔(2～50 nm)贡献了其主要的孔容和比表面积,占总孔容的7437%,占总比表面积的6440%,且长9段页岩的总孔容和总比表面积均大于长7段页岩;(3)延长组页岩孔隙结构以狭缝型孔和板状孔为主,孔径主要分布在04～09 nm、3～25 nm和5～200 μm区间段内,延长组页岩平均孔径为853 nm,且长7段页岩平均孔径大于长9段页岩;(4)页岩有机碳含量、有机质成熟度及矿物成分含量共同影响着延长组页岩孔隙的发育,其中矿物成分含量是以介孔孔隙为主的延长组页岩孔隙发育的主控因素,有机碳含量及成熟度的增加主要对页岩中微孔孔隙的发育起到积极作用。     

Organic matter in small mesopores in sediments and soils

The three-way correlation among organic matter concentrations, specific surface area and small mesopores observed for many soils and sediments led to the hypothesis that enclosure within the pores might explain the apparent protection of organic matter by minerals. We test this hypothesis by examining whether the bulk of organic matter resides within small mesopores. Pore volumes as a function of pore width were measured before and after organic matter removal, and the volume differences ascribed to organic matter filling of pores. Minor changes in small mesopore size distributions upon treatments such as centrifugation and muffling indicate the robustness of the mineral matrices that form these pores. We developed an additional method to assess organic matter densities using high-resolution pycnometry, and used these densities to convert pore volumes to organic matter contents. Although smaller mesopores are shown to have sufficient volumes to contain significant fractions of the total organic matter, only small fractions of total organic matter were found to reside in them. These results are consistent with preferential association between organic matter and aluminous clay particle edges, rather than the largely siliceous clay faces that contribute most surface area and form pore walls. While simple enclosure within smaller mesopores cannot, therefore, explain protection, network effects working at larger size scales may account for exclusion of digestive agents and hence organic matter protection.     

Modelling of rock alteration due to coupled heat and mass transport

 A three-dimensional computer model is presented for studying the interaction of heat and mass transport regarding the temporal and spatial evolution of sandstones. The model simulates coupled heat and reactive mass transport in porous rocks. In general, mineral solubilities in water are low. Therefore, large fluid volumes are required to flow through the rock to explain observed mineral cements in sandstones. Besides mass transport, pore fluids transport heat which modifies rock temperatures. Very high flow rates result in strong temperature modifications and, therefore, enhance diagenesis. Low flow rates often cannot account for observed cementation. The model results show the effect of advective, convective and conductive heat transport on temperature and diagenetic evolution of sandstones for two different flow systems in a simple geological environment. Received: 6 August 1996/Accepted: 18 December 1996     

Some effects of compaction and geological time on the pore parameters of argillaceous rocks

Graphical statistics have been applied to the pore-size distribution curves of argillaceous rocks to characterize the changes in pore parameters that result from compaction and geological time. The most striking characteristic of recently deposited sediment is the high variability in mean pore size and in the sorting and skewness of the pore system. The mean pore size ranges from 15 to 980 nm, sorting ranges from very well sorted to poorly sorted, and skewness varies from systems in which small pores predominate over large ones to systems in which large pores predominate. This high variability in pore structure represents the many environmental and mineral-related variables that affect the pore system of newly deposited sediment. The mean pore size of shales decreases with increasing compaction and approaches a limiting value of about 3·5 nm at depth. Within a geological time span of 50 m.y. and/or depth of burial of about 1200 m, most sediments have reached an irreversible, well sorted pore-size distribution. Early diagenetic processes apparently affect the skewness of pore systems more than compaction, such that within about 50 m.y. the pore system is negatively skewed, with small pores predominating over large. Sediments buried to a depth of 500 m or less exhibit a porosity range of 40--85%; below 500 m, porosity decreases linearly with burial depth. No correlation exists between the surface area of shale pore systems and depth of burial, geological age, and the pore parameters mean pore size, sorting, and skewness.     

皖南地区古生界页岩孔隙特征及影响因素

为了评估下扬子皖南地区古生界页岩气储层性质,应用扫描电子显微镜、高压压汞法、N₂和CO₂气体吸附法,对皖南地区古生界页岩孔隙特征和孔隙结构进行研究,并探讨页岩孔隙发育的主要影响因素。结果表明,皖南地区古生界页岩孔隙度和渗透率低,页岩样品中常见粒间孔、凝絮孔、溶蚀孔、基质晶间孔和有机质孔,并且发育微米-纳米级孔隙。古生界页岩孔隙中50%以上为微孔和介孔;孔隙结构主要为圆柱孔、狭缝型孔和混合型孔,平均孔径范围为4.17~12.06 nm。页岩孔容和比表面积随着有机碳(TOC)含量的增大而增大;页岩孔隙度随着有机质成熟度(R_o)的增大而减小;页岩孔容随着黏土矿物含量的增加而增大,随着脆性矿物含量的增加而减小。     

Visualizing complex pore structure and fluid flow in porous media using 3D printing technology and LBM simulation

Pore structures of porous media and properties of fluid flow are key factors for the study of non-Darcy groundwater flow. However, it is difficult to directly observe pore structures and flow properties, resulting in a “black box” problem of porous media. This problem has hindered the in-depth study of the groundwater flow mechanism at the pore scale. In recent years, 3D rapid prototyping technology has seen tremendous development. 3D printing provides digital models and printing models of porous media with clear internal structure. Thus, Lattice Boltzmann Method can be used to simulate the flow processes at the pore scale based on real pore structures. In this study, 3D printing cores and Lattice Boltzmann Method were coupled to conduct both laboratory and numerical experiments in spherical porous media with different sphere diameters and periodic arrays. The LBM simulation results show a good agreement with laboratory experimental results. With the advantages of LBM and 3D printing, this approach provides a visualization of the complex pore structure and fluid flow in pores, which is a promising method for studies of non-Darcy groundwater flow at the pore scale.     

多孔介质中气泡尺寸对流动阻力的影响

多孔介质中的泡沫能够封堵某些孔道,降低气体流动性。由于直接观察多孔介质中的泡沫流动比较困难,所以关于泡沫流动性与气泡尺寸之间的关系研究较少。利用Navier-Stokes方程与守恒的水平集方法耦合模拟孔隙介质中气泡尺寸对流动阻力的影响,结果证实,气泡尺寸是影响流体阻力的重要因素。当气泡半径小于孔喉半径时,气泡不受孔道约束,气泡流动过程中流动阻力较稳定,此时含气泡流体流动阻力与纯液态流体流动阻力相等,所以小于孔喉尺寸的气泡对孔道无封堵作用。当气泡半径大于孔喉半径时,孔道影响气泡变形,其流动阻力存在波动性,最大流动阻力随气泡体积变大呈线性增加。当气泡体积增加到使最大流动阻力达极大值时,继续增大气泡体积,最大流动阻力随气泡体积增大而线性降低。最大流动阻力随气泡体积增大而线性增大与减小变化具有周期性,周期为单位孔体体积。     

临兴区块上古生界煤系页岩孔隙结构多尺度定性–定量综合表征

为了揭示鄂尔多斯盆地东缘海陆过渡相页岩微观孔隙结构特征及其主控因素,丰富对该区块海陆过渡相煤系页岩孔隙发育特征与孔隙结构的认识,对临兴地区页岩进行扫描电镜、高压压汞和液氮吸附分析以表征微观孔隙结构特征,同时结合孔隙率、TOC含量、岩石矿物含量、黏土相对含量、有机质成熟度测试结果对页岩孔隙结构发育主控因素进行研究。结果表明:研究区页岩发育粒内孔、粒间孔、溶蚀孔和微裂缝,有机质内部偶见孔隙、可见微裂隙,与矿物伴生时周边发育微裂隙;页岩总孔容介于0.001 46~0.010 81 mL/g,介孔占比81.9%,比表面积介于0.35~ 3.65 m2/g,孔径分布以单峰型为主,分布范围主要在200 nm以内,主峰孔径在45 nm左右,本溪组、太原组页岩孔隙连通性优于山西组,太原组宏孔占比优于本溪组、山西组;页岩总有机碳含量对页岩孔隙发育的影响复杂,对宏孔发育具有一定的积极作用,脆性矿物含量对总孔、介孔发育有积极作用,黏土矿物含量对总孔和介孔发育起消极作用,其中,脆性矿物和黏土矿物通过影响介孔的发育来控制页岩中孔隙的发育程度。基于页岩孔隙结构多尺度定性–定量表征及其控制因素研究对临兴区块海陆过渡相页岩气资源量评价、甜点优选与开发具有重要指导意义,丰富了对海陆过渡相页岩储层的地质认识。      

黔西上二叠统煤的孔隙特征及其控制因素

作为一种多孔介质,煤的孔隙性质直接影响煤层气的富集和扩散,因而对煤孔隙特征的研究至关重要。通过压汞测试和低温氮吸附测试数据,系统分析了黔西上二叠统煤的孔隙形态、孔隙类型及孔径分布特征,并从煤岩显微组分及煤级方面探讨了该区煤储层孔隙发育的控制因素。研究结果表明:黔西煤样孔隙度为1.4%～9.5%,且由北至南有减小趋势;孔隙类型以吸附孔为主,其中高煤级煤孔隙以一端封闭型孔居多,与低煤级区相比,其渗透性和连通性较差,但黔西地区整体优于沁水盆地;煤级是影响煤储层孔隙变化的主控因素,随着煤级增加,孔隙度呈现由低到高的变化趋势。      

复杂储层多尺度数字岩石评价

复杂储层岩石矿物组成非均质性强,孔喉结构细小.储集空间有效性评价、岩石结构精细评价及流体赋存状态与运移规律评价是决定复杂储层油气勘探成效的关键.针对复杂储层的储集空间（孔喉、裂缝）、岩石结构（矿物、有机质）、流体特征3方面,建立了复杂储层多尺度数字岩石评价技术及工作流程.储集空间表征方面:二维大面积分析技术可建立跨越6~7个数量级的多尺度选取及非均质性评价;多尺度CT及FIB-SEM联用可精确刻画孔喉和裂缝的三维空间分布;电化学和显影剂技术可以有效地帮助分析微观孔隙连通性.固体组分分析方面:XRF及Qemscan联用可定量评价矿物组成与分布;三维FIB-SEM技术可以实现有机质形态和分布的定量分析.流体特性方面:荷电效应可用于微量残留有机流体的识别与表征;通过合成孔径、润湿性、表面微结构均可调控的纳米材料,开展地层条件下页岩油赋存及流动物理模拟研究,确定了单一因素对页岩油赋存及可动孔径下限的影响;利用分子模拟研究油气在无机、有机质纳米孔隙中的聚集机理与扩散潜力.复杂储层多尺度数字岩石评价技术体系和一系列具体应用可以有效地填补常规储层分析手段的不足,为页岩油气、致密砂岩油气储层以及深部油气储层等复杂储层有效性评价和含油气性定量评价提供技术支撑.      

Numerical simulation of fully saturated porous materials

Fully coupled, porous solid–fluid formulation, implementation and related modeling and simulation issues are presented in this work. To this end, coupled dynamic field equations with u?p?U formulation are used to simulate pore fluid and soil skeleton (elastic–plastic porous solid) responses. Present formulation allows, among other features, for water accelerations to be taken into account. This proves to be useful in modeling dynamic interaction of media of different stiffnesses (as in soil–foundation–structure interaction). Fluid compressibility is also explicitly taken into account, thus allowing excursions into modeling of limited cases of non‐saturated porous media. In addition to these features, present formulation and implementation models in a realistic way the physical damping, which dissipates energy. In particular, the velocity proportional damping is appropriately modeled and simulated by taking into account the interaction of pore fluid and solid skeleton. Similarly, the displacement proportional damping is physically modeled through elastic–plastic processes in soil skeleton. An advanced material model for sand is used in present work and is discussed at some length. Also explored in this paper are the verification and validation issues related to fully coupled modeling and simulations of porous media. Illustrative examples describing the dynamical behavior of porous media (saturated soils) are presented. The verified and validated methods and material models are used to predict the behavior of level and sloping grounds subjected to seismic shaking. Copyright © 2008 John Wiley & Sons, Ltd.     

碳酸盐岩中地开石的分布特征及其成因

塔里木盆地巴楚-麦盖提地区石炭系小海子组碳酸盐岩中存在大量地开石,利用X射线粉晶衍射对该矿物进行了鉴定,利用阴极发光显微镜和扫描电镜对地开石的形态与分布进行了研究。地开石晶体为短柱状,晶体大小约3~13 μm,分布在溶蚀孔、白云石晶间孔和缝合线的溶解段中。经岩石薄片和阴极发光观察,发现在地开石出现的岩样中存在萤石。地开石与萤石组合的出现,表明该地区小海子组存在着热液活动。经统计,地开石和萤石通常富集于某一层,可追踪热液流体来源的深度。由于地层中未见地开石的前身矿物,并且在温度低于100℃的地层中也出现了地开石,推断该区地开石为热液成因。热液流体不仅为地开石形成创造了条件,还导致了小海子组碳酸盐岩产生大量溶蚀孔隙。热液与岩石间的水岩反应导致萤石交代白云石,溶孔壁白云石重结晶。通过对储层物性数据的分析,表明热液溶蚀能明显增加孔隙度,但萤石和地开石的形成对孔隙度起破坏作用。热液溶蚀是小海子组碳酸盐岩储层形成的重要机理,对指导该区油气勘探具有实际意义。