Characteristics of petroleum accumulation in syncline of the Songliao basin and discussion on its accumulation mechanism

The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and structural high spot, oil and water transitions are located in their middle. Stagnation is the key fact of oil-forming reservoir in the axis of a syncline based on the research of oil, gas and water migration manner, dynamics and non-Darcy flow in the Songliao basin. In low and ultra-low permeable reservoir, gas and water migrate easily through pore throats because their molecules are generally smaller than the pore throats; but the minimum diameter of oil droplets is larger than pore throats and they must be deformed to go through. Thus, gas and water migrate in advance of oil, and oil droplets remain behind. Pressure differential and the buoyancy force in a syncline reservoir are a main fluid driving force; and capillary force is the main resistance to flow. When the dynamics force is less than resistance, oil is immobile. When the buoyancy force is less than the capillary force, a gravitational separation of oil and water does not occur. The reservoir in the mature source rock of a syncline area with the low and ul- tra-low permeability belongs to an unconventional petroleum reservoir.     

低渗砂岩储层渗透率各向异性规律的实验研究

应用1摩尔/升的盐水作为孔隙介质,采用液体压力脉冲法对采自鄂尔多斯盆地某油田三叠系延长组低渗砂岩样品进行了渗透率随有效应力的变化规律实验研究.在围压0～100MPa,孔隙压力0～12MPa范围内,样品的渗透率变化范围在0～60×10-18 m2之间,实验结果表明样品的渗透率随有效应力的增加而减少.通过拟合实验结果,得到渗透率随有效应力的变化规律较好的符合幂函数关系,相关系数介于0.903～0.984之间.同时对同一样品的X,Y,Z相互垂直三个方向的渗透率随有效应力的变化进行了比较,结果表明渗透率的各向异性同样是压力的函数,且随着有效应力的增加,不同平面内的渗透率各向异性表现出了不同的变化规律.但在实验压力范围内,渗透率各向异性皆为正值,表明在有效应力为100MPa范围内孔隙内流体的流动方向未发生改变.研究结果为鄂尔多斯盆地低渗(超低渗)油气田开发,特别是对深部油气田开发过程中开发方式的选择与设计,充分利用渗透率各向异性的特点,提高采收率提供了新的岩石物性资料.     

泥质砂岩液相渗透率计算新方法

液相渗透率描述了岩石的渗流特性,是评价储层与预测油气产能的重要参数.液相渗透率是指盐水溶液在岩石孔隙中流动且与岩石孔隙表面黏土矿物发生物理化学作用时所测得的渗透率;液相渗透率的实验测量条件更加接近实际地层泥质砂岩的条件,使得液相渗透率更能反映地层条件下泥质砂岩的渗流特性;然而,现有的液相渗透率评价模型较少,且模型未能揭示液相渗透率与溶液矿化度之间的关系.基于此,开展了液相渗透模型推导与计算方法研究;文中首先将岩石等效为毛管束模型,推导建立了液相渗透率与比表面、喉道曲折度、总孔隙度、黏土束缚水孔隙度等参数之间的关系;其次,根据岩石物理体积模型,推导建立了黏土束缚水孔隙度与阳离子交换容量、溶液矿化度等参数的关系;最终,将黏土束缚水孔隙度引入液相渗透率计算公式,建立了基于总孔隙度、阳离子交换容量、溶液矿化度、比表面、喉道曲折度等参数的液相渗透率理论计算模型.液相渗透率计算模型与两组实验数据均表明,液相渗透率随阳离子交换容量的增大而降低,随溶液矿化度的增大而增大.然而,液相渗透率理论计算模型的实际应用中喉道曲折度、比表面等参数求取困难,直接利用理论模型计算液相渗透率受到限制.在分析液相渗透率与孔隙渗透率模型的基础上,建立了液相渗透率与空气渗透率之间的转换模型,形成了利用转化模型计算液相渗透率的新方法.为进一步验证液相渗透率与空气渗透率转化模型的准确性,基于两组实验数据,利用转换模型计算了液相渗透率;液相渗透率计算结果与岩心测量液相渗透率实验结果对比显示,液相渗透率计算结果与实际岩心测量结果吻合较好,文中建立的液相渗透率与空气渗透率转化模型合理可靠.     

Geologic characteristics,controlling factors and hydrocarbon accumulation mechanisms of China’s Large Gas Provinces of low porosity and permeability

Based on the analysis of the geological characteristics and controlling factors, we analyzed the formation mechanism of different types of gas reservoirs. The main characteristics of gas provinces with low porosity and permeability are mainly as follows: large area, low abundance, small gas pools and large gas provinces; widely distributed excellent hydrocarbon source rocks with closely contacted source-reservoir-cap association; development mainly in large continental depressions or in paralic shallow-river delta systems; many kinds of traps coexisting in large areas, dominantly para-layered lithologic, digenetic and capillary pressure traps; double fluid flow mechanisms of Darcy flow and non-Darcy flow; complicated gas and water relations; and having the resource distribution of highly productive “sweet spots”, banding concentration, and macroscopically large areas integrated. The main controlling factors of large sandstone gas provinces with low porosity and permeability are stable dynamic backgrounds and gentle structural frameworks which control the extensive distribution of alternate (interbedded) sandstones and mudstones; weak hydropower of large gentle lake basins controlling the formation of discontinuous, low porosity and permeability reservoirs in shallow-water deltas; regionally differential diagenesis and no homogeneous digenetic facies controlling the development of favorable reservoirs and digenetic traps; and weak and dispersive reservoir-forming dynamic forces leading to the widely distributed small traps with low abundance. Low porosity and permeability gas provinces with different trap types have different formation mechanisms which include fluid diversion pressure difference interactive mechanism of lithologic-trap gas accumulations, separated differential collection mechanism of digenetic-trap gas accumulations, and the Non-Darcy flow mechanism of capillary-pressure gas accumulations. Supported by PetroChina Science and Technology Project (Grant No. 07-01C-01-07) and Youth Innovation Fund Project (Grant Nos. 10100042KT96, 07-06D-01-04-01-03)     

用油田生产测井资料确定产层动态渗透率的方法研究

目前,我国处于开发中后期的油田平均产水率高达80%以上.因此对产层进行评价,确定地层动态渗透率等参数及剩余油的平面分布,由此研究其特点具有十分重要的意义.在储层径向流动方程分析的基础上,研究了储层渗透率与产液量/吸水量和油并内流压变化等生产测井资料之间的关系,提出了利用油田生产测井资料估算各产层的动态渗透率的方法.该方法不需关井,计算过程相对简单、可以节约成本,还可以避免常规压力恢复或压力降落试井造成低产井降产甚至停产的可能性.计算结果能较好地反映各小层的产液性质.     

The modified Reynolds equation for non-wetting fluid flow through a rough-walled rock fracture

The no-slip boundary condition has usually been assumed to hold for the Reynolds equations (local cubic law) for fluid flow through rough-walled fractures. However, its validity for non-wetting fluid flow, such as prevails in fractured oil reservoirs, has been questioned. A series of experiments with a rough-walled fracture with mean aperture of 760 μm finds a higher flow rate for non-wetting fluid than wetting fluid. A modified Reynolds equation with a slip boundary condition is derived for non-wetting fluid flow through rough-walled fractures. Comparison of the modified Reynolds equation predictions with experimental results confirms that slip was a plausible explanation for a higher flow rate. The amount by which the flow rate for non-wetting fluids exceeds that for wetting fluids is found to depend highly on, and increase with, the degree to which the flowing fluid was non-wetted to thin immobile films on the surfaces. Numerical studies using the modified Reynolds equation indicate that the flow rate of non-wetting fluid became higher than that of wetting fluid as the roughness of the fracture increases. As the aperture becomes smaller, the flow rate ratio of non-wetting fluid to wetting fluid becomes large, leading to the endpoint relative permeability for the non-wetting fluid to exceed 1. The experimental and numerical studies clearly show that as the aperture of the fracture became less than a few hundred microns, the modified Reynolds equation with slip boundary conditions provides a better model for flow of a non-wetting fluid through rough-walled fractures.     

鄂尔多斯盆地中东部长6复杂低渗储层测井评价

开展复杂低渗储层特征、测井响应及其控制因素分析,有助于储层评价与油水层识别.鄂尔多斯盆地中东部长6期沉积具多物源供给、沉积相带频繁变化的特点,来自不同物源的沉积砂体岩石碎屑成分存在明显差异.长7、长6沉积期盆地周边的火山作用,致使一些地区的长6砂体具有相对高放射性特征.长6储层孔隙类型多样,孔隙结构特征复杂多变,再加上地层水系统的变化,致使一些油区长6低电阻率油层与常规油层、高电阻率水层与常规水层共存.研究结果表明,成藏动力与阻力的对比关系决定了在同一砂体中除存在常规油水分布外,还可能存在油水倒置分布.因此,加强钴前预测、钻井过程监督与调整、钻后综合研究、生产实践检验、解释模型与参数调整、老井复查等,有利于识别油水层,整体把握油水分布规律.     

砾岩储层地震波传播方程:三重孔隙结构模型

针对砾岩储层的砂、砾、泥三重孔隙结构特征,本文分析砾岩孔隙区域、砂岩孔隙区域以及泥岩孔隙区域相互之间的孔隙流体流动机制,将静态的砾岩骨架本构方程与动态的孔隙流体运动方程联立,提出了复杂砾岩储层的弹性波传播理论方程.采用实测砾岩储层参数,在算例中与双重孔隙介质理论进行对比分析,验证了本文理论方程的合理性;基于三重孔隙介质模型,分析不同储层环境下纵波的传播特征,结果显示:随流体黏滞系数增大,在衰减-频率轴坐标系中,砾与砂、砂与泥孔隙区域间局域流导致的两个衰减峰向低频端移动,而Biot全局流导致的衰减峰向高频端移动;嵌入体尺寸及背景相介质渗透率的变化,主要影响纵波速度频散曲线沿频率轴左、右平移,不影响波速低频、高频极限幅值;嵌入体含量及孔隙度的变化改变了岩石干骨架的弹性、密度参数,不仅影响速度频散曲线沿频率轴平移,而且影响其上、下限幅值;砾包砂包泥三重孔隙介质模型所预测的衰减曲线中,低频段"第一个衰减峰"主要由砾岩孔隙区域与砂岩孔隙区域之间的局域流导致,中间频段"第二个衰减峰"主要由砂岩孔隙区域与泥岩孔隙区域之间的局域流导致,超声频段"第三个衰减峰"由Biot全局流导致.对慢纵波传播特征的分析显示,砂岩骨架(局部孔隙度较大)内部的宏观孔隙流体流动造成的耗散明显强于砾岩与泥岩骨架.     

Research on seismic fluid identification driven by rock physics

Seismic fluid identification works as an effective approach to characterize the fluid feature and distribution of the reservoir underground with seismic data. Rock physics which builds bridge between the elastic parameters and reservoir parameters sets the foundation of seismic fluid identification, which is also a hot topic on the study of quantitative characterization of oil/gas reservoirs. Study on seismic fluid identification driven by rock physics has proved to be rewarding in recognizing the fluid feature and distributed regularity of the oil/gas reservoirs. This paper summarizes the key scientific problems immersed in seismic fluid identification, and emphatically reviews the main progress of seismic fluid identification driven by rock physics domestic and overseas, as well as discusses the opportunities, challenges and future research direction related to seismic fluid identification. Theoretical study and practical application indicate that we should incorporate rock physics, numerical simulation, seismic data processing and seismic inversion together to enhance the precision of seismic fluid identification.     

Acoustic and petrophysical relationships in low-shale sandstone reservoir rocks

This paper describes the measurements of the acoustic and petrophysical properties of two suites of low‐shale sandstone samples from North Sea hydrocarbon reservoirs, under simulated reservoir conditions. The acoustic velocities and quality factors of the samples, saturated with different pore fluids (brine, dead oil and kerosene), were measured at a frequency of about 0.8 MHz and over a range of pressures from 5 MPa to 40 MPa. The compressional‐wave velocity is strongly correlated with the shear‐wave velocity in this suite of rocks. The ratio V_P/V_S varies significantly with change of both pore‐fluid type and differential pressure, confirming the usefulness of this parameter for seismic monitoring of producing reservoirs. The results of quality factor measurements were compared with predictions from Biot‐flow and squirt‐flow loss mechanisms. The results suggested that the dominating loss in these samples is due to squirt‐flow of fluid between the pores of various geometries. The contribution of the Biot‐flow loss mechanism to the total loss is negligible. The compressional‐wave quality factor was shown to be inversely correlated with rock permeability, suggesting the possibility of using attenuation as a permeability indicator tool in low‐shale, high‐porosity sandstone reservoirs.     

Influence of permeability on hydrothermal circulation in the sediment-buried oceanic crust

1 Introduction Hydrothermal circulation is the key process of hydrothermal activity. Modern seafloor hydrothermal circulation can be divided into three parts: convective cells in the oceanic curst, interface between seafloor and ocean and hydrothermal plume. Hydrothermal convection in the crust is the dominant part of the whole seafloor hydrothermal circulation. The distribu-tion and nature of hydrothermal system in the oceanic crust are controlled by crust thermal structures and permeability …     

中低孔渗储层岩石弹性参数的流体敏感性研究(英文)

本文从WXS凹陷中低孔渗储层岩石声波实验出发,以岩样的纵横波速度和密度为基础数据,求取出一系列的弹性参数,包括纵横波波速比、纵波波阻抗、横波波阻抗、泊松比、拉梅常数、剪切模量、体积模量、杨氏模量,等等。在前人的孔隙流体识别究基础上,综合相关理论和实验分析,构建了一个新的流体识别因子F。以饱和流体岩石弹性参数及其组合参数的相对变化量Ag/w和Ao/w为定量指标,评价各流体识别因子的流体识别效果,并采用交会图技术进行了验证。新流体敏感因子在传统较难分辨的孔隙流体"水"和"油"的区别上具有良好效果,有利于提高中低孔渗储层流体识别的成功率。     

多尺度CT成像技术识别超低渗透砂岩储层纳米级孔喉

以鄂尔多斯盆地X地区长6储层为研究对象,利用多尺度CT成像技术、聚焦离子束扫描电镜技术,结合Avizo软件的强大数据处理和数值模拟功能,对研究区目的层岩石样品进行不同尺度孔喉分维数重构,建立三维超低渗透砂岩储层纳米级孔隙结构模型.研究表明,微米尺度下,超低渗透砂岩储层孔喉形态呈点状、球状和条带状及管状.储集空间类型以溶蚀微孔为主且多孤立分布,局部孔隙为片状,连通性较差.纳米尺度下,超低渗透砂岩储层孔喉系统整体较发育,孔喉形态呈球状、短管状.远离裂隙处多为孤立状,连通性较差,仅具有储集能力.微裂缝、粒间缝发育部位多为短管状,有一定连通性,相当于喉道.微观非均质性较强,岩样整体较致密,局部相互连通,溶蚀孔及裂隙对储集能力、渗滤能力具有控制作用.数值计算求得目的层A、Y、C三个样品的孔隙度分别为6.95%、5.55%、4.44%,渗透率分别为0.828×10^-3μm^2、0.115×10^-3μm^2、0.00065×10^-3μm^2.聚焦离子束扫描电镜与多尺度CT成像技术相结合能够定量表征超低渗透砂岩储层微、纳米级孔隙结构.     

Numerical simulation of frequency-dependent seismic response and gas reservoir delineation in turbidites: A case study from China

To simulate the frequency-dependent response of turbidite reservoirs in the JZ Area, near the Bohai Sea, China, we apply a diffusive and viscous wave equation (DVWE), which takes into account diffusive and viscous attenuation and velocity dispersion in fluid-bearing poroelastic media. We use a seismic data-driven geological model building approach to produce physical parameter sections, which are then used to numerically synthesize the frequency-dependent seismic response in the DVWE-based simulation. The DVWE-based synthetic section shows the characteristic reflection and geometry of turbidites and delineates the phase delay, instantaneous dominant frequency decrease and magnitude attenuation related to the gas-bearing reservoir. The common frequency sections obtained by instantaneous spectral decomposition of the synthetic section show that a low-frequency shadow (LFS) lies immediately beneath the reservoir. Next, following the implications of the numerical simulation, we then apply LFS and fluid mobility to the data volume. Both hydrocarbon indicators clearly delineate the bright gas reservoir and its spatial distribution. The workflow and methodologies can be expected to be applicable to other frequency-dependent hydrocarbon indicators.     

Fluid identification based on P-wave anisotropy dispersion gradient inversion for fractured reservoirs

Fluid identification in fractured reservoirs is a challenging issue and has drawn increasing attentions. As aligned fractures in subsurface formations can induce anisotropy, we must choose parameters independent with azimuths to characterize fractures and fluid effects such as anisotropy parameters for fractured reservoirs. Anisotropy is often frequency dependent due to wave-induced fluid flow between pores and fractures. This property is conducive for identifying fluid type using azimuthal seismic data in fractured reservoirs. Through the numerical simulation based on Chapman model, we choose the P-wave anisotropy parameter dispersion gradient (PADG) as the new fluid factor. PADG is dependent both on average fracture radius and fluid type but independent on azimuths. When the aligned fractures in the reservoir are meter-scaled, gas-bearing layer could be accurately identified using PADG attribute. The reflection coefficient formula for horizontal transverse isotropy media by Rüger is reformulated and simplified according to frequency and the target function for inverting PADG based on frequency-dependent amplitude versus azimuth is derived. A spectral decomposition method combining Orthogonal Matching Pursuit and Wigner–Ville distribution is used to prepare the frequency-division data. Through application to synthetic data and real seismic data, the results suggest that the method is useful for gas identification in reservoirs with meter-scaled fractures using high-qualified seismic data.     

Porosity, permeability, and fluid flow in the Yellowstone geothermal system, Wyoming

Cores from two of 13 U.S. Geological Survey research holes at Yellowstone National Park (Y-5 and Y-8) were evaluated to characterize lithology, texture, alteration, and the degree and nature of fracturing and veining. Porosity and matrix permeability measurements and petrographic examination of the cores were used to evaluate the effects of lithology and hydrothermal alteration on porosity and permeability. The intervals studied in these two core holes span the conductive zone and the upper portion of the convective geothermal reservoir. Variations in porosity and matrix permeability observed in the Y-5 and Y-8 cores are primarily controlled by lithology. Y-8 intersects three distinct lithologies: volcaniclastic sandstone, perlitic rhyolitic lava, and non-welded pumiceous ash-flow tuff. The sandstone typically has high permeability and porosity, and the tuff has very high porosity and moderate permeability, while the perlitic lava has very low porosity and is essentially impermeable. Hydrothermal self-sealing appears to have generated localized permeability barriers within the reservoir. Changes in pressure and temperature in Y-8 correspond to a zone of silicification in the volcaniclastic sandstone just above the contact with the perlitic rhyolite; this silicification has significantly reduced porosity and permeability. In rocks with inherently low matrix permeability (such as densely welded ash-flow tuff), fluid flow is controlled by the fracture network. The Y-5 core hole penetrates a thick intracaldera section of the 0.6-Ma Lava Creek ash-flow tuff. In this core, the degree of welding appears to be responsible for most of the variations in porosity, matrix permeability, and the frequency of fractures and veins. Fractures are most abundant within the more densely welded sections of the tuff. However, the most prominent zones of fracturing and mineralization are associated with hydrothermal breccias within densely welded portions of the tuff. These breccia zones represent transient conduits of high fluid flow that formed by the explosive release of overpressure in the underlying geothermal reservoir and that were subsequently sealed by supersaturated geothermal fluids. In addition to this fracture sealing, hydrothermal alteration at Yellowstone appears generally to reduce matrix permeability and focus flow along fractures, where multiple pulses of fluid flow and self-sealing have occurred.     

The nonlinear oil–water two-phase flow behavior for a horizontal well in triple media carbonate reservoir

Carbonate reservoir is one of the important reservoirs in the world. Because of the characteristics of carbonate reservoir, horizontal well has become a key technology for efficiently developing carbonate reservoir. Establishing corresponding mathematical models and analyzing transient pressure behaviors of this type of well-reservoir configuration can provide a better understanding of fluid flow patterns in formation as well as estimations of important parameters. A mathematical model for a oil–water two-phase flow horizontal well in triple media carbonate reservoir by conceptualizing vugs as spherical shapes are presented in this article. A semi-analytical solution is obtained in the Laplace domain using source function theory, Laplace transformation, and superposition principle. Analysis of transient pressure responses indicates that seven characteristic flow periods of horizontal well in triple media carbonate reservoir can be identified. Parametric analysis shows that water saturation of matrix, vug and fracture system, horizontal section length, and horizontal well position can significantly influence the transient pressure responses of horizontal well in triple media carbonate reservoir. The model presented in this article can be applied to obtain important parameters pertinent to reservoir by type curve matching.     

Seismic Data Processing and Interpretation on the Loess Plateau, Part 2： Seismic Data Interpretation

The loess plateau covering the North Shaanxi slope and Tianhuan depression consists of a regional monocline, high in the east and low in the west, with dips of less than 1^0, Structural movement in this region was weak so that faults and local structures were not well developed. As a result, numerous wide and gentle noses and small traps with magnitudes less than 50 m were developed on the large westward-dipping monocline. Reservoirs, including Mesozoic oil reservoirs and Paleozoic gas reservoirs in the Ordos Basin, are dominantly lithologic with a small number of structural reservoirs. Single reservoirs are characterized as thin with large lateral variations, strong anisotropy, low porosity, low permeability, and low richness. A series of approaches for predicting reservoir thickness, physical properties, and hydrocarbon potential of subtle lithologic reservoirs was established based on the interpretation of erosion surfaces.     

裂缝-孔隙介质储层渗透率表征及其影响因素分析

含裂缝多孔介质渗透率预测是非常规油气资源勘探开发的一个紧迫问题.现有多孔介质岩石物理模型通常利用圆形孔管模拟宏观岩石孔隙空间,难以定量描述软孔隙/裂缝在压力作用下的闭合情况,缺乏裂缝/孔隙间流量交换的连通机制.本文提出含三维裂缝/软孔隙网络多孔介质模型,将储层岩石裂缝/软孔隙表示为椭圆截面微管,建立了周期性压力作用下微...     

鄂尔多斯盆地南部黄土塬区地震资料处理与解释 第二部分:地震资料解释

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