Averaging Effect on Elastic Wave Velocity in an Integrated Flow Model

Abstract

This article discusses the effect of averaging seismic attributes resulting from a petrophysical algorithm which is used in association with a traditional fluid flow simulator to form an integrated flow model (IFM). Few attempts have been made to evaluate an IFM called GEOFLO by comparison with experimental models. Arithmetic averaging was used to get a single value for a calculated parameter in each grid that is used for comparison with an experimentally measured average parameter, yet different averaging techniques have not been discussed. Therefore, in this research, four different averaging techniques were used to investigate the effect of reducing many values into a single representative value. The methods considered include arithmetic, harmonic, geometric, and root-mean-square averaging techniques. Comparisons were made for compressional and shear wave velocities as well as velocity ratios using core samples of different lithologies. Results show overlapped data from all averaging techniques used, which implies very little effect of the averaging process of the elastic wave velocities using the petrophysical algorithm. Therefore any averaging technique can be used for a one-dimensional reservoir divided into different grids, and that most likely it will yield an average calculated value that would be comparable to the measured elastic wave velocity.     

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.     

不同压力条件下部分饱和砂岩速度实验结果及理论解释

在实验高频条件下，对储层砂岩样品采用常规饱和方法得到的弹性波速度随饱和度的变化呈现出复杂的样式，不同于地震勘探中用有效流体模型给出的理论结果，这种差异在低围限压力下更为明显。本文在变压力条件下，对部分饱和储层砂岩的纵、横波速度变化规律进行了系统实验研究及定量分析。研究表明，在实验高频条件下，两种不同孔隙尺度上流体分布的不均匀性明显影响实验结果，也是实验结果与有效流体模型理论值存在差异的主要原因：孔隙尺度上纵横比较小的裂隙中的饱和流体在高频条件下非“弛豫”作用对弹性波速度存在影响；较大尺度上（包含多个孔隙）孔隙流体不均匀的斑块分布对纵波速度存在影响。因此不论在实验室条件下，或是在实际地震勘探中分析弹性波速度时，应考虑这些因素影响。     

考虑成岩固结作用的双重孔隙介质岩石物理模型及其应用

成岩固结作用和孔隙结构及类型是影响致密油气储层弹性性质的重要因素.然而,现有的岩石物理模型大多聚焦于单一孔隙类型或只考虑成岩作用,难以准确刻画致密油气储层低孔低渗、流体分布不均匀及孔隙结构和类型复杂等特征.为此,充分利用微分等效介质(DEM)理论和Pride模型导出考虑成岩固结作用的双重孔隙介质岩石物理模型,通过引入固...     

Investigation of Low Frequency Elastic Wave Application for Fluid Flow Percolation Enhancement in Fractured Porous Media

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) Iassonov, P. P. and Beresnev, I. A. 2003. A model for enhanced fluid percolation in porous media by application of low-frequency elastic waves. J. Geophys. Res., 108: 2138–2146. [Crossref], [Web of Science ®] , [Google Scholar] for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's “block and fracture” model assuming negligible vertical permeability in blocks is considered for modeling. In addition, two-phase flow behavior under elastic wave in fractured system is investigated. The results showed that, at higher pressure gradients, vibration amplitude cannot highly influence the fluid percolation, in contrast at lower pressure gradients, the fluid flow through the fractured porous media can considerably be improved by increasing vibration amplitude. Also, it has been found that in two-phase flow systems, wave can increase the produced oil-water ratio in the fractured media. The results of this study can be applied to the fractured reservoir simulations and can be a path breaking to the future studies on the prediction of flow enhancement under elastic wave in the fractured reservoirs.     

塔中地区ZG5-7井区横波速度的预测

纵、横波速度是储层岩性、物性和流体识别的重要参数,而实际生产中往往缺乏横波速度资料,因此,开展横波速度预测已成为岩石物理研究的重要内容。目前横波预测中普遍使用的是Greenberg-Castagna经验公式,但其在塔里木盆地塔中地区ZG5-7井区应用效果不佳。针对上述问题,充分利用已钻井的纵波速度、地层密度、泥质含量、孔隙度、含水饱和度等常规测井资料以及岩石骨架和流体的各种弹性参数,构建了流体置换的Xu-White模型,用来求取横波速度。该区６口井的横波曲线拟合的实验结果表明：Xu-White模型预测的横波速度与实测横波速度高低趋势一致,其相关系数最高达到0.970 9,完全能满足横波弹性反演和油气预测的需要。结论认为,Xu-White模型不仅适用于碎屑岩储层的横波速度预测,同样在碳酸盐岩的横波速度预测中也能取得良好的应用效果。     

Study of the Optimal Timing for Refracturing

Abstract

Refracturing is important for the stimulation of low-permeability reservoirs. Based on the properties of the mechanical and fluid parameters of a reservoir, a model of optimal refracturing timing based on solid-fluid coupling is established, taking account of formation, initial fractures, porous flow, well bore, and fluid properties. Calculations indicate that far-field stress difference, elastic modulus, compressibility, initial fracture, and bottom-hole pressure affect the optimal refracturing timing. The model and conclusions are significant to further understanding of refracturing.     

On the value of 3D seismic amplitude data to reduce uncertainty in the forecast of reservoir production

Three-dimensional (3D) seismic data are commonly used to identify the size and shape of putative flow barriers in hydrocarbon reservoirs. It is less clear to what extent determining the spatial distribution of engineering properties (e.g., porosity, permeability, pressures, and fluid saturations) can improve predictions (i.e., improve accuracy and reduce uncertainty) of hydrocarbon recovery, given the multiple non-linear and often noisy transformations required to make a prediction. Determining the worth of seismic data in predicting dynamic fluid production is one of the goals of this paper.We have approached the problem of assessing uncertainty in production forecasts by constructing a synthetic reservoir model that exhibits much of the geometrical and petrophysical complexity encountered in clastic hydrocarbon reservoirs. This benchmark model was constructed using space-dependent, statistical relationships between petrophysical variables and seismic parameters. We numerically simulated a waterflood in the model to reproduce time-varying reservoir conditions. Subsequently, a rock physics/fluid substitution model that accounts for compaction and pressure was used to calculate elastic parameters. Pre-stack and post-stack 3D seismic amplitude data (i.e., time-domain amplitude variations of elastic responses) were simulated using local one-dimensional approximations. The seismic data were also contaminated with additive noise to replicate actual data acquisition and processing errors. We then attempted to estimate the original distribution of petrophysical properties and to forecast oil production based on limited and inaccurate spatial knowledge of the reservoir acquired from wells and 3D seismic amplitude data.We compared the multiple realizations of the various predictions against predictions with a reference model. The use of seismic amplitude data to construct static reservoir models affected production performance variables in different ways. For example, seismic amplitude data did not uniformly improve the variability of the predictions of water breakthrough time; other quantities, such as cumulative recovery after the onset of production, did exhibit an uncertainty reduction as did a global measure of recovery. We evaluate how different degrees of spatial correlation strength between seismic and petrophysical parameters may ultimately affect the ensuing uncertainty in production forecasts.Most of the predictions exhibited a bias in that there was a significant deviation between the medians of the realizations and that the value from the reference case. This bias was evidently caused by noise in the various transforms (some of which we introduced deliberately) coupled with nonlinearity. The key nonlinearities seem to be in the numerical simulation itself, specifically in the transformation from porosity to permeability, in the relative permeability relationships, and in the conservation equations themselves.     

基于横向各向同性BISQ模型的弹性波高阶交错网格有限差分数值模拟

 孔隙介质模型主要有Biot模型与BISQ模型。BISQ模型同时考虑了Biot流动与喷射流动,能够获得比Biot理论更为准确的结果。弹性波数值模拟有利于认识波的传播特性与过程，而采用高阶交错网格有限差分法数值模拟的空间频散性比低阶差分法小。本文从BISQ模型弹性波的本构方程和运动方程出发，推导出了基于横向各向同性BISQ模型的弹性波高阶交错网格有限差分算法，还进行了数值模拟。通过调整差分阶数、频率以及黏滞系数，研究了兼顾两种流动机制时弹性波的传播特性，并分析了BISQ模型下弹性波的透射与反射。     

雷州半岛南部玄武岩岩石物理特征

基于雷州半岛南部51件玄武岩岩心样品在饱和气、饱和水状态下的纵、横波波速和弹性模量等参数的测试结果,研究了孔隙度、孔隙类型、岩相和流体对岩石弹性力学参数的影响,分析了用于识别玄武岩岩性、流体的岩石物理参数的敏感性。研究结果表明：玄武岩中纵波波速与横波波速、密度与纵波波速具有较好的线性关系,杨氏模量与密度呈幂函数关系。孔隙度是影响岩石波速的主要因素,孔隙类型对岩石波速的影响不可忽视。岩石密度是区分玄武岩岩石亚相最敏感的岩石物理参数,利用密度与杨氏模量的交会关系可识别玄武岩的溢流相上部亚相、中部亚相和下部亚相。利用泊松比与纵波阻抗交会图、拉梅系数和剪切模量之比与纵波阻抗交会图可以区分玄武岩中的气层与水层。     

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。     

基于布谷鸟算法的储层物性参数同步反演

物性反演是储层预测与评价的重要手段,可直观描述储集层所蕴含的信息。由于地球物理反演的非线性特征,以局部寻优方法开展的储层物性参数反演方法难以降低不适定性,结果存在多解性。为此,提出一种基于布谷鸟算法的储层物性参数同步反演方法。以弹性阻抗与储层物性参数关系为基础,构建储层物性反演目标函数,引入布谷鸟算法寻找目标函数最优解。布谷鸟算法作为一种新型元启发式算法,其包含的Levy飞行机制能有效解决常规方法陷入局部极值的问题,可实现更高精度的储层物性参数预测。理论模型和实际数据测试均表明,该方法能够有效反演物性参数,可为储层描述提供数据支持。     

An Analysis of Oil Well Testing for Non-Newtonian Fluid in a Fracture-Dominated Reservoir

Abstract

A mathematical model based on a composite geometry was developed for a non-Newtonian power-law fluid in a fracture-dominated reservoir. An analytic solution in Laplace space for this reservoir model was used to determine the type-curves for various composite parameters. The dynamic behavior of the bottom hole pressure at early and later stages was also analyzed. Therefore, the model can be used to analyze the fluid flow and fractures in some polymer-flooding reservoirs.     

INVESTIGATION OF ELASTIC INVERSION ATTRIBUTES USING THE EXPANSIBLE CLAY MODEL FOR WATER SATURATION

Quantitative X‐ray diffraction has been used to characterize water saturation levels in complex shaly sand reservoirs (i.e. shaly sands with infrequent carbonates and minor proportions of iron‐rich minerals such as pyrite and siderite). The results led to the design of a total expansible clay model for water saturation, which is similar in form to the Dual Water model except that the excess effect of the clay minerals has been accounted for by a volume‐conductivity relationship, rather than one of the usual volume‐porosity translations, effectively reducing the uncertainties in estimating water saturation. Given the ambiguities associated with predicting these petrophysical properties from data on rock properties, such as mineralogy, an investigation of the relationship of estimated water saturation based on the total expansible clay model to independently determined rock properties was undertaken using well log inversion and forward modelling techniques. The results show that there is consistency in the relationship between water saturation estimates made from the total expansible clay model and known elastic parameters such as primary and shear‐wave sonic velocity (V_p, V_s), bulk density (ρ_b) and impedance (I), when the Raymer‐Gardner‐Hunt model is used. Use of the Raymer‐Gardner‐Hunt model to reconstruct the required rock‐physics relationship avoids the classic limitation of the more advanced Gassman model, which assumes that the dry shear modulus is equivalent to the wet shear modulus (μ_dry=μ_wet). The present work raises further questions on the application of the Voigt‐Reuss‐Hill (VRH) limits, or the Hashin Shtrikman bounds for averaging the effective shear modulus of the dry matrix in complex shaly sand reservoirs, where a two‐mineral matrix is normally assumed. The study shows the inapplicability of the VRH or Hashin‐Shtrikman averaging techniques but provides a minor adjustment to the averaging that solves the problems faced in reconstructing the relationships between directly measured elastic properties and derived petrophysical properties for this type of reservoir rock.     

非牛顿流体孔隙介质弹性波动方程

重油、聚合物和压裂液等非牛顿流体普遍存在于油气勘探和开发过程中,研究孔隙尺度非牛顿流体流动及其对地震波场的影响具有重要意义.Biot理论忽略了流体黏性系数及剪切应力的非线性变化,虽然可用于描述完全饱和固体与经典牛顿流体在波场作用下的相互作用,但是对于非牛顿流体孔隙填充物来说不准确,因此需要研究含非牛顿流体效应的孔隙介质...     

Effective Permeability Calculation Using Boundary Element Method in Naturally Fractured Reservoirs

Abstract

A model is presented to calculate the effective permeability tensor in naturally fractured reservoirs using Boundary Element Methods (BEM). Arbitrary fractures of different scales based on their length are considered. Interface boundary condition is used to model the short fractures as an enhancement of matrix permeability. Long fractures, on the other hand are treated as source/sink in the corresponding blocks. Periodic boundary condition is applied to the grid-block boundaries to calculate the elements of effective permeability tensor. Darcy's law and Navier-stoke's equation are applied to fluid flow in rock matrix and fractures, respectively. An important feature of this approach is that the fluid flow in matrix-fracture interface is coupled by Poisson's equation and fluid flow in the rest of the matrix is formulated by Laplace's equation. This paper also presents an innovative approach to optimization and parallelization of the model by High Performance Computing (HPC) techniques. The model has been validated against analytical results and applied to a typical case where arbitrary fractures of different sizes are assumed within the grid blocks. The effective block permeability tensors can be implemented into a reservoir simulator to calculate fluid flow through the naturally fractured reservoirs.     

海域天然气水合物岩石物理建模方法

海域天然气水合物赋存于疏松沉积物中,天然气水合物岩石物理建模之前需要建立疏松沉积物的岩石物理模型。为此,针对传统疏松沉积物岩石物理模型存在横波速度估计误差偏高、建模过程不自洽的问题,考虑海水对沉积物颗粒的润滑作用,引入改进的Hertz-Mindlin方程进行岩石物理建模,提高了建模精度;针对疏松沉积物的建模过程,首先利用改进的Hertz-Mindlin方程计算临界孔隙度条件下沉积物的弹性模量,然后利用Hashine-Shtrikman界限计算疏松沉积物骨架的弹性模量;在讨论不同赋存形态的水合物对沉积物弹性性质的影响及适用模型、判别准则的基础上,针对以颗粒支撑和孔隙流体充填两种赋存状态存在的天然水合物,设计了兼容两种赋存形态的岩石物理建模方法和流程。浅钻井的实测曲线与建模结果吻合度高,证实了该方法的适用性。     

层状饱和多孔介质中Biot慢波的影响

本文基于Biot理论对P波在层状饱和多孔介质中的传播进行数值模拟。首先根据Kennett反射方法建立层状介质中地震波的数值模型，然后利用此模型研究层状饱和介质中Biot慢波对地震波性质的影响。文中分别在孔隙为弹性（考虑了P波扩散、Biot全局流及慢波影响）和黏弹性（可忽略慢波影响）两种情况下定量地分析了频率、孔隙率、层厚、渗透率以及岩石弹性模量对Biot慢波效应的影响。对比两种模型的数值模拟结果发现，在低频范围内，沉积盆地地层间液体压力的平衡作用（Biot慢波）能使P波产生显著的衰减；若这种衰减发生在浅层勘探地震波的频带内（几十到几百赫兹），则介质层厚必然在几厘米到几十厘米范围内；介质越柔顺，孔隙率越大，渗透性越好，则慢波影响越大；在高频段，只要地层足够薄，介质的柔顺性足够好，界面处产生的慢波对高P波散射也会有很大影响。     

叠前反演技术在高邮凹陷黄珏油田浅层气藏识别中的应用研究

高邮凹陷黄珏油田浅层气藏构造复杂,常规弹性参数无法完全区分岩性和流体。通过地震、地质、测井等资料综合分析,特别是对重点井目的层段的岩石物理分析,提出将纵横波速度与密度相结合而定义的敏感因子--流体识别因子识别浅层气藏的思路,并将流体识别因子反演结果与常规弹性参数反演结果进行对比,研究发现流体识别因子反演可以有效地识别出目的层段的含气性,其结果较单一弹性参数反演结果具有更高的精度、更高的可靠性,为黄珏油田浅层气藏勘探及有利区域预测指明了方向。     

渤海湾盆地QHD29-2区块储层地震预测及烃类检测研究

渤海湾盆地QHD29-2区块东营组三段为一典型的构造-岩性复合圈闭,采用常规波阻抗反演和地震属性分析等技术难以有效预测储层及其含油气性。在岩石物理综合分析的基础上,以岩性和流体敏感弹性参数交会图版为指导,通过综合应用基于泊松阻抗(IPI)分析的储层预测方法以及以拉梅常数为主要参数的储层烃类检测方法,开展QHD29-2区块储层地震预测和烃类检测技术研究,探索出一套适合该区储层预测的地球物理技术流程。后经钻井证实该方法的预测结果准确、有效。