Pore-Space Microstructure and Clay Content Effect on the Elastic Properties of Sandstones

Abstract

The elastic moduli of shaly sandstones and the effect of pore aspect ratios and clay content on the elastic properties of shaly sandstones are calculated using an isotropic dual porosity model. It is shown that the elastic moduli and velocities of shaly sandstones are affected by the clay content, pore aspect ratios, and the fluid. The bulk and shear moduli increase with an increase in the aspect ratios of sandstones related to pores whether the sandstones are saturated by water or dry. The P-wave and S-wave velocities of water-saturated shaly sandstones both increase with the increase of the pore aspect ratios. The bulk and shear moduli decrease with an increase in clay content. The relationships between the elastic moduli of the rocks and the clay content are linear, which is in agreement with the laboratory measurements by Han. The bulk modulus of shaly sandstone is sensitive to fluid change when the pore aspect ratio is small.     

ESTIMATION OF AN EQUIVALENT SHALINESS PARAMETER USING RESISTIVITY AND SPECTROSCOPY LOGS: A TOTAL EXPANSIBLE CLAY APPROACH

We develop a method for estimating the degree of saturation in shaly sand formations based on an equivalent shaliness parameter. In shaly sands, the measured electrical conductivity is influenced by the clay content because of the charge deficit associated with the clay particles. This deficit is offset by counter-ions in a double layer whose contribution to total charge transfer is dominated by the total expansible clays. We derive an approximation for clay content and cation exchange capacity (CEC) from a linear relationship between the CEC and the total expansible clay (TEC) content of a reservoir rock. By combining mineralogy from quantitative X-ray diffraction (XRD) with wet chemistry CEC data, an expression for the counter-ions in the double layer as a function of the total expansible clays is derived. The analytical expression obtained is coupled with well-log data and compared to existing models. For determining surface conductivity, the new methodology eliminates the need for performing core measurements, subjective selection of CEC values from existing data, or the use of log-based volume-porosity translations. We show that existing popular industry models, and effective medium and electrochemical models of rock electrical conductivity can be adapted to use the new methodology. The results demonstrate a strong correlation between the estimated and measured bulk conductivity, and also resolve the scatter in estimated bulk conductivity often observed under low pore-water salinity conditions, where the ratio of surface to electrolyte conductivity approaches unity. The methodology has been applied to water saturation estimation in two Australian petroleum wells, Yolla-4 and Cliff Head-4. The results demonstrate that this technique provides better estimates of water saturation in both low conductivity contrast pays and tight pays compared to existing approaches.     

地层水矿化度对泥质砂岩物理性质的影响

依据多矿化度岩石电性及核磁特性实验,研究不同矿化度下泥质砂岩的束缚水饱和度、岩石电性以及核磁共振的变化特征.研究表明,不同矿化度下的泥质砂岩束缚水饱和度不同,随饱和溶液矿化度的增大而减小;在地层水矿化度较低情况下,由于较高的束缚水含量和泥质附加导电性,岩石的电阻率也可能呈现低电阻率特征;T2受到饱和溶液矿化度的影响,矿化度的变化带来T2谱分布形态的变化,T2截止值随饱和溶液矿化度的增大而减小.     

基于实验的泥质砂岩含水饱和度计算方法

以泥质砂岩导电性实验和简化的岩石导电模型为基础,分析了泥质砂岩电阻率影响因素.确定了泥质附加导电的大小.淡水条件下的泥质附加导电性的大小不但与泥质体积有关,而且与地层水电阻率、孔隙度的大小有关,据此给出了一种简单的含水饱和度计算方法.实际应用表明,所给出的含水饱和度计算方法简便易行,泥质校正合理,所提供的含水饱和度比较准确,可以推广应用.     

岩石物理模型在横波速度估算中的应用

岩石物理模型是进行岩石物理研究、求取横波速度的重要基础。利用Xu-White砂泥岩混合模型,通过岩心测试数据、纵波和密度曲线、泥质百分含量及孔隙度测量得到岩石骨架的体积模量和剪切模量,然后计算不同流体及流体饱和度下岩石的有效弹性模量,进而计算出纵、横波速度。经过与实测密度、纵波资料的对比,调整参数循环迭代计算,得到最终横波速度。利用岩石物理模型估算横波速度,解决了平湖油气田放鹤亭构造常规测井缺乏横波资料的难题,为AVO正演模拟、叠前AVO/AVA同步反演提供了可靠的基础数据。     

混合泥质砂岩粘土包裹颗粒电阻率模型

砂岩油气层的低电阻率可能是由于富含分散粘土、层状泥质、高束缚水、高矿化度水、骨架导电等因素综合引起的，因此有必要建立一种适用于骨架导电且同时含分散粘土和层状泥质砂岩解释的通用电阻率模型，以提高复杂泥质砂岩储层含水饱和度的解释精度。基于层状泥质与分散粘土砂岩并联导电的观点，而分散粘土砂岩的导电可用粘土包裹颗粒电阻率模型进行描述,从而建立了考虑分散粘土和层状泥质同时存在的含油气泥质砂岩粘土包裹颗粒通用电阻率模型；通过2组分散泥质砂岩岩样实验测量数据和1组层状泥质砂岩测井资料的测试,表明该模型既适用于分散粘土砂岩地层解释又适用于层状泥质砂岩地层解释；利用建立的混合泥质砂岩粘土包裹颗粒电阻率模型，对海拉尔盆地高泥地区的苏1、苏3井进行处理，并将模型计算的含水饱和度与试油结果进行对比，结果表明模型计算的含水饱和度是合理的，故本模型适用于含油气复杂泥质砂岩地层解释。     

基于岩石物理实验的储层与孔隙流体敏感参数特征——以珠江口盆地东部中-深层碎屑岩储层为例

岩石物理实验是研究储层地震响应特征的重要手段,利用实验测试不同类型、含不同孔隙流体岩石样品的岩石物理参数,可为寻找优质储层及烃类流体的敏感性参数提供实验依据。根据珠江口盆地中-深层碎屑岩储层油气勘探的需要,选取珠一坳陷的惠州凹陷、陆丰凹陷和西江主洼,珠二坳陷的白云主洼、白云东洼和番禺低隆起等地区13口井的碎屑岩储层样品,开展了岩石物理参数的实验测试研究。通过地层压力条件下不同岩性、不同物性、不同孔隙流体饱和度的测试分析,得到样品的储层物性特征和岩石物理参数特征及岩样含不同孔隙流体饱和度时的地震响应特征。测试结果表明：岩样具有高孔中渗、中孔中低渗、低孔低渗、特低孔低渗等多种储层物性特征,物性具有明显的差异;岩样纵/横波速度、杨氏模量、剪切模量、体积模量、拉梅常数等岩石物理参数与孔隙度、渗透率、密度之间具有较高的相关度;岩样随着含水饱和度的提高,其拉梅常数、体积模量、泊松比、纵波波阻抗、纵波速度、纵/横波速度比随之增加,变化幅度大,表现出对含水/气、含水/油饱和度的变化比较敏感。岩样的横波速度、横波波阻抗、剪切模量变化较小,表现出对含水/气、含水/油饱和度的变化敏感性较弱。ρf、λρ、λρ ·μρ、σ、Z_p-Z_s等流体识别因子具有很强的气水识别能力,也具有一定的油水识别能力。不同流体识别因子的组合模板,具有较好的识别气、水、油的效果,且识别海相储层孔隙流体的效果明显好于陆相储层。     

Effective Approach for Fractured Carbonate Reservoir Petrophysical Logs Interpretation in an Iranian Offshore Oil Field

Abstract

Due to the lack of information about the porosity exponent (m) from core experiments, the impossibility of comparison between the results and the core data, and, finally, inattentiveness to fractured intervals, the correct determination of the porosity exponent value in the calculation of water saturation and also the core-log correlation have generally been neglected. In this article, an analysis of the Mishrif Unit was carried out in two wells in order to properly calculate the water saturation and determine the best producing intervals. Based on fractured zones detection and the results of petrophysical evaluation in the calculation of shale volume and true matrix properties for these zones, accurate values of the porosity (matched with core data) were used to determine the porosity exponent. Hence, one of the advantages of this study is applying the method introduced simply for the fractured parts of the reservoir unit, in order to obtain the correct value for water saturation. Detecting proper producing intervals in the Mishrif Unit was executed using integrated evaluation of petrophysical data, geological data, and core data using a new method of shaly carbonate formation interpretation based on petrophysical log results. In this method, a statistical parameter, P^½, was used. The results from the application of the method show better interpretation and water saturation calculation using petrophysical logs of fractured shaly carbonate formations in combination with other available methods in the petroleum community.     

煤系地层地震岩石物理建模及横波预测方法

煤系地层油气资源发育潜力较大,现有地震岩石物理建模方法欠缺对储层含煤后岩石物理性质的系统研究。为此,利用自洽(SCA)模型耦合煤的影响,将其以包含物的形式加入背景介质中,构建一种适用于含煤储层的地震岩石物理模型;通过分析煤层占比、泥质含量、含水饱和度及孔隙度等微观物性参数对岩石弹性模量的影响,优选表征储层物性特征的敏感弹性参数;推导出以纵波速度为约束的岩石物理反演目标泛函,利用模拟退火全局寻优算法实现了横波速度的预测。将该方法应用于实际测井数据,预测横波速度与实测数据吻合度较高,证明了该模型对煤系地层的适用性。     

泥质砂岩地层的粘土性质分析

地层中粘土的存在对测井解释结果起着十分重要的影响,是造成测井解释复杂性的重要原因之一.正确地分析地层中的粘土性质,有助于测井解释人员更加全面地进行泥质砂岩储层的油气评价.以粘土测井特征和中子-密度测井交会法为基础,对每个泥质砂岩资料点确定其粘土性质,按含水泥质砂岩模型计算地层粘土含量;用粘土的阳离子交换量与干粘土含氢指数的交会来识别粘土类型.实践证明,该方法对物性较差的低渗透储集层以及低电阻率油气层有优越性,但对含轻烃的地层不适用.     

Neural Network Identification of Hydrocarbon Potential of Shaly Sand Reservoirs

Abstract

Hydrocarbon potential evaluation of shaly sand layers requires the adoption of certain shaly water model and also the selection of suitable conventional logging suite. The main target is how to get the accurate porosity and how to convert the apparent water saturation to true water saturation for given shaly sand layer. In this paper neural network approach is presented to replace the conventional interpretation of well logging data to better determine formation porosity and water saturation and to well identify hydrocarbon potential of clean and shaly sand layers. Two neural networks were constructed, one for prediction of porosity using six well logging data inputs: GR, LLD, RHOB, NPHI, PEF, and Δt); and water saturation using five well logging data inputs: GR, LLD, RHOB, NPHI and PEF. Shale volume was defined from GR data. Each neural network is trained using available logging data and validated using the core data before applying it to the entire well log. Neural network predicted formation porosity and water saturation for tested sections of one well. Also using the cut off values of porosity, water saturation and shale volume, the neural network defined the possible pay zones in the well. Network outputs have shown good matching with core data and the reference calculated petrophysical parameters. The developed network approach has successfully deduced porosity, water saturation and defined pay zones in a new well that projects its application for new wells.     

混合泥质砂岩有效介质通用HB电阻率模型在高泥储层中的应用

基于Berg提出的层状泥质或分散泥质砂岩有效介质HB电阻率模型，并在总孔隙中考虑粘土结合水的体积，但不考虑粘土结合水与地层水导电性的差别，将粘土结合水与地层水的导电性差别归结到粘土颗粒导电中，建立了混合泥质砂岩有效介质通用HB电阻率模型。通过研究混合泥质砂岩有效介质通用HB电阻率模型的求解方法，表明模型导出的关于Swt的方程是一个一元二次方程，可用求根公式求解，解法非常简单。通过对混合泥质砂岩有效介质通用HB电阻率模型中各参数的确定方法进行研究，给出了有效的参数确定方法。利用建立的混合泥质砂岩有效介质通用HB电阻率模型，对海拉尔盆地高泥地区的苏1、苏3井进行处理，并将模型计算的含水饱和度与试油结果进行对比，结果表明模型计算的含水饱和度是合理的。该模型适用于高泥地区的泥质砂岩地层解释。     

混合泥质砂岩通用电阻率模型研究

基于层状泥质与分散泥质砂岩的并联导电,而分散泥质砂岩导电性等效于分散粘土和地层水为一种导电液体的纯砂岩,并考虑到在低地层水电导率(Gw)范围内分散粘土电导率(Ccl)随Gw增大而增大,建立了混合泥质砂岩通用电阻率模型.通过对该模型的影响因素分析,发现泥质分布形式对模型计算的含水饱和度有很大影响;只有Ccl变化时,地层电导率(G1)与有效含水饱和度(Sw)关系曲线的曲率相近;随Sw增大,胶结指数m对Ct与S关系曲线的影响增大,而饱和度指数n对Ct与Sw关系曲线的影响减小.通过2组分散泥质砂岩岩样实验测量数据和1组层状泥质砂岩测井资料的测试,表明该模型既适用于分散泥质砂岩地层解释又适用于层状泥质砂岩地层解释,给出的电阻率模型为通用电阻率模型.利用建立的混合泥质砂岩通用电阻率模型对海拉尔盆地高泥地区的苏1、苏3井进行处理,并将模型计算的含水饱和度与试油结果进行对比,结果表明模型计算的含水饱和度是合理的.本模型适用于高泥地区的泥质砂岩地层解释.     

多浓度下泥质砂岩电学性质实验研究

依据多浓度岩石电性实验，研究不同浓度下泥质砂岩的束缚水相对体积及其导电特性，可以揭示束缚水饱和度和地层水浓度的变化所引起的泥质砂岩导电特性的变化。研究表明，不同浓度下的泥质砂岩有不同的束缚水饱和度，而且随饱和溶液浓度的增大而减小。束缚水条件下岩石的电阻率受地层水电阻率、束缚水饱和度、泥质附加导电性影响，在地层水浓度较低情况下，由于较高的束缚水含量和泥质附加导电性，岩石的电阻率也可能呈现低电阻率特征。     

泥质砂岩含水饱和度方程理论模型推导

根据HB方程并考虑多种导电影响因素,得到了泥质砂岩的含水饱和度理论公式。该理论公式与已有公式相比,较全面地考虑了诸如泥质导电、岩石骨架导电、地层束缚水导电等因素对岩石整体导电性的贡献,为进一步研究泥质砂岩含水饱和度奠定了基础。     

The Behavior of Acoustic Wave Velocity in Some Paleozoic Sandstone Samples

Abstract

Seismic properties of reservoir fluids are of greater importance and the elastic inversion is fast becoming a commodity data product that oil companies understand and use for risk reduction. This study is an attempt to determine the effect of some petrophysical parameters (porosity, permeability dry density, saturated density, and water saturation) on the behavior of both P-wave (compression wave velocity) and S-wave (shear wave velocity) in sandstone rock samples. Acoustic wave velocity has been carried out for 46 sandstone samples. The measurements have been done for both dry and fully saturated rock samples.     

DEPOSITIONAL FACIES,PORE TYPES AND ELASTIC PROPERTIES OF DEEP‐WATER GRAVITY FLOW CARBONATES

Quantitative petrographic analyses of deep‐water resedimented carbonates from the Gargano Peninsula (SE Italy) were integrated with petrophysical laboratory measurements (porosity, P‐and S‐wave velocities) to assess the impact of sedimentary fabrics and pore space architecture on velocity‐porosity transforms. Samples of Upper Cretaceous carbonate came from the Monte Sant'Angelo, Nevarra and Caramanica Formations and can be classified into four depositional facies associations: F1, lithoclastic breccias; F2, bioclastic packtones to grainstones; F3, interbedded grainstones‐packstones and wackestones; and F4, (hemi‐) pelagic mudstones. Five pore type classes were distinguished: I and II, dominant intercrystalline microporosity; IIIa, dominant intergranular macroporosity; IIIb, dominant mouldic macroporosity; and IIIc, mixed intergranular and mouldic macroporosity. Pore type was found to strongly control velocity‐porosity transforms, unlike depositional facies associations. The equivalent pore aspect ratio (EPAR), derived from differential effective medium models, is proposed to identify pore types from elastic properties. The EPAR originates from the bulk modulus or shear modulus of the samples (K‐ and μ‐EPAR, respectively). Regardless of porosity values and depositional facies, microporous samples (type I) and samples with dominant intergranular porosity (type IIIa) are characterized by low values of K‐ and μ‐EPAR (<0.22) and by K‐EPAR > μ‐EPAR By contrast, samples with dominant mouldic porosity (type IIIb) display high values of K‐ and μ‐EPAR (>0.25 and 0.4 respectively) and K‐EPAR < μ‐EPAR. High permeability limestones with dominant intergranular porosity cannot be discriminated from low permeability microporous carbonates. The petrophysical classes derived from elastic properties are shown to be distinct from reservoir property‐driven rock types. In the present case, a seismic‐based poro‐elastic model does not match the reservoir property model. Hence, a sedimentary facies model for the studied carbonates cannot accurately represent the petrophysical properties, which are determined by pores types and pore network architecture.     

碳酸盐岩储层流体替换中混相流体体积模量的计算

流体替换是研究流体对储层岩石物理参数影响的重要手段。在流体替换过程中,通常使用Woods方程计算混相流体的体积模量,但对于碳酸盐岩储层,由于其基质孔隙度低,岩石内存在不均匀充填的情况,Woods方程不再适用,为此,对斑块充填(Patchy)条件下混相流体体积模量的计算方法进行了更为深入的研究。通过对Patchy模型极端情形的研究,得到了饱和斑块充填情况下混相流体的计算模型。混相流体均匀充填和饱和斑块充填模型分别对应于混相流体充填的两种极端情况,所计算的结果分别是实际混相流体体积模量的上限和下限。考虑实际储层中混相流体的复杂充填状态,将利用Woods方程和Patchy模型计算的流体体积模量取算术平均(VRH模型),所得结果作为近似的混相流体体积模量。南方某探区碳酸盐岩储层实际流体替换结果表明,利用Woods方程和Patchy模型计算的结果有明显差异,利用VRH模型计算的结果是较为可信的。     

泥质砂岩中束缚水的介电特性

泥质砂岩“双水模型”只讨论了束缚水和自由水在导电响应上的差异,本文对泥质砂岩介电响应机理进行分析,说明了粘土颗粒表面的束缚水和自由水在介电响应上的差异。另外,在大量实验测量的基础上,计算得到束缚水的复介电常数值,结果表明理论分析和实验测量是一致的。利用上述理论和实验研究结果修正了电磁波测井的解释模型,并将该模型用于实际测井资料解释,求得的冲洗带残余油饱和度(S_(or))和束缚水饱和度(S_(wirr))与取心分析值符合较好。依据上述理论和实验分析提出了电磁波测井资料解释应用的新领域。     

东濮凹陷岩石声学和弹性力学参数特性试验研究

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