Comparative study of models for predicting permeability from nuclear magnetic resonance (NMR) logs in two Chinese tight sandstone reservoirs

Based on the analysis of mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) experimental data for core plugs, which were drilled from two Chinese tight sandstone reservoirs, permeability prediction models, such as the classical SDR, Timur-Coates, the Swanson parameter, the Capillary Parachor, the R10 and R35 models, are calibrated to estimating permeabilities from field NMR logs, and the applicabilities of these permeability prediction models are compared. The processing results of several field examples show that the SDR model is unavailable in tight sandstone reservoirs. The Timur-Coates model is effective once the optimal T _2cutoff can be acquired to accurately calculate FFI and BVI from field NMR logs. The Swanson parameter model and the Capillary Parachor model are not always available in tight sandstone reservoirs. The R35 based model cannot effectively work in tight sandstone reservoirs, while the R10 based model is optimal in permeability prediction.     

Committee neural networks for porosity and permeability prediction from well logs

Neural computing has moved beyond simple demonstration to more significant applications. Encouraged by recent developments in artificial neural network (ANN) modelling techniques, we have developed committee machine (CM) networks for converting well logs to porosity and permeability, and have applied the networks to real well data from the North Sea. Simple three‐layer back‐propagation ANNs constitute the blocks of a modular system where the porosity ANN uses sonic, density and resistivity logs for input. The permeability ANN is slightly more complex, with four inputs (density, gamma ray, neutron porosity and sonic). The optimum size of the hidden layer, the number of training data required, and alternative training techniques have been investigated using synthetic logs. For both networks an optimal number of neurons in the hidden layer is in the range 8–10. With a lower number of hidden units the network fails to represent the problem, and for higher complexity overfitting becomes a problem when data are noisy. A sufficient number of training samples for the porosity ANN is around 150, while the permeability ANN requires twice as many in order to keep network errors well below the errors in core data. For the porosity ANN the overtraining strategy is the suitable technique for bias reduction and an unconstrained optimal linear combination (OLC) is the best method of combining the CM output. For permeability, on the other hand, the combination of overtraining and OLC does not work. Error reduction by validation, simple averaging combined with range‐splitting provides the required accuracy. The accuracy of the resulting CM is restricted only by the accuracy of the real data. The ANN approach is shown to be superior to multiple linear regression techniques even with minor non‐linearity in the background model.     

致密油储层核磁共振测井响应机理研究

中国西部某盆地致密油储层孔隙结构差,而核磁共振测井T2谱宽,其复杂的核磁测井响应认识不清,且响应机理也不明确.本文基于致密油储层的特性,通过对三组岩样不同系列的实验测量,包括核磁共振、毛管压力曲线、X衍射矿物分析和润湿性实验,主要研究了碳酸盐岩矿物含量对T2谱的影响和由润湿性引起的T2弛豫机制.根据实验结果分析和讨论,明确了致密油岩石核磁共振响应的影响因素及孔隙流体的弛豫机制.综合分析认为,所述的核磁测井响应特征是由两方面因素综合作用的结果,一是水的T2信号主要取决于表面弛豫,低表面弛豫率的碳酸盐岩矿物导致水的T2信号的长弛豫分量增多;二是由于岩石亲油孔隙表面的存在且其弛豫率低于亲水孔隙表面的弛豫率,使得油的T2信号由表面弛豫和体弛豫贡献.     

地面核磁共振找水反演

简要介绍了地面核磁共振找水的正演理论方法,采用高斯求积并结合连分式展开的方法对核磁共振核函数中包含双重贝塞尔函数的积分核进行了数值积分,进而计算出精度较高的核函数值,在此基础之上,讨论了导电性对地面核磁共振信号的影响.基于奇异值分解算法,对核磁共振找水理论模型进行了反演研究,在不导电的情况下,重构出了比较理想的含水率分布.总结并改进了模拟退火算法,用改进的模拟退火算法分别对覆盖层高阻和导电条件下的核磁共振人工合成数据进行了反演,试验结果表明,利用改进的模拟退火算法反演地面核磁共振是可行的,而且反演结果较稳定,收敛速度较快.     

Modeling and interpretation of Q logs in carbonate rock using a double porosity model and well logs

Attenuation data extracted from full waveform sonic logs is sensitive to vuggy and matrix porosities in a carbonate aquifer. This is consistent with the synthetic attenuation (1 / Q) as a function of depth at the borehole-sonic source-peak frequency of 10 kHz. We use velocity and densities versus porosity relationships based on core and well log data to determine the matrix, secondary, and effective bulk moduli. The attenuation model requires the bulk modulus of the primary and secondary porosities. We use a double porosity model that allows us to investigate attenuation at the mesoscopic scale. Thus, the secondary and primary porosities in the aquifer should respond with different changes in fluid pressure. The results show a high permeability region with a Q that varies from 25 to 50 and correlates with the stiffer part of the carbonate formation. This pore structure permits water to flow between the interconnected vugs and the matrix. In this region the double porosity model predicts a decrease in the attenuation at lower frequencies that is associated with fluid flowing from the more compliant high-pressure regions (interconnected vug space) to the relatively stiff, low-pressure regions (matrix). The chalky limestone with a low Q of 17 is formed by a muddy porous matrix with soft pores. This low permeability region correlates with the low matrix bulk modulus. A low Q of 18 characterizes the soft sandy carbonate rock above the vuggy carbonate.This paper demonstrates the use of attenuation logs for discriminating between lithology and provides information on the pore structure when integrated with cores and other well logs. In addition, the paper demonstrates the practical application of a new double porosity model to interpret the attenuation at sonic frequencies by achieving a good match between measured and modeled attenuation.     

裂缝性储层孔隙指数、饱和度及裂缝孔隙度计算研究

裂缝性储层的裂缝孔隙度、饱和度和孔隙指数等参数的计算一直是测井界亟待解决的难题,它直接关系到对裂缝性储层的发育程度、含油气性、储量规模等方面的评价,前人已在这些方面做了大量的研究工作,但仍需进一步提高和深化对裂缝性储层参数计算的认识.基于考虑裂缝倾角和裂缝曲折度问题的Aguilera孔隙指数计算模型,研究了裂缝性储层孔隙指数的变化规律,研究表明裂缝性地层的孔隙指数受裂缝倾角、岩石总孔隙度、裂缝孔隙度和裂缝曲折度影响大.单组系裂缝性储层饱和度的计算采用将复合系统的孔隙指数代入阿尔奇公式的方法来计算,计算结果与目前国内仍广泛使用的基于串、并联关系建立的双重孔隙饱和度模型计算结果存在较大差别.对比分析了利用成像测井和三种基于双侧向资料的裂缝孔隙度计算模型计算的裂缝孔隙度,表明不同裂缝孔隙度模型计算的裂缝孔隙度大小差别较大.基于双侧向的裂缝孔隙度计算模型只适用于特低孔或致密地层,在由非裂缝因素引起的电阻率降低段使用该模型计算裂缝孔隙度时会出现错误,引入校正系数可拓宽模型的使用范围.     

Solid-state nuclear magnetic resonance and infrared spectroscopy of alkali feldspars

²⁹Si,²⁷Al MAS NMR and IR spectra of rnonophase K-feldspars (sanidine, orthoclase and microcline) and Na-feldspars (monalbite, anorthoclase and low albite) in different structural states have been studied. The NMR and IR spectra of K-feldspars and Na-feldspars vary regularly along with their degrees of Si/Al ordering evolution. Si in orthoclase occupiesT _2m,T2o andT1m, and the high-temperature Na-feldspar (monalbite and anorthoclase) coincides in²⁹Si,²⁷Al NMR and IR spectra. Moreover, all the high-temperature Na-feldspars and sanidine have the same²⁷Al NMR and IR spectra. Project supported by the Foundation of Laboratory of Magnetic Resonance and Atom and Molecular Physics, Wuhan Institute of Physics, Chinese Academy of Sciences.     

裂缝和孔洞型储层孔隙模型的理论进展

对有洞的和裂缝型储层的分析已经成为一个热点,因而孔隙模型的研究近年得到了很好的发展.目前已经用双孔隙和三孔隙模型研究这类储层的特性并寻找估计孔隙指数的方法,以便计算含水饱和度.用串联或并联电阻网络模拟储层表明：双孔隙模型适用于基质与非连通孔洞储层以及裂缝和（或）连通孔洞的储层.三孔隙模型更适用于由基质、裂缝和不连通孔洞组成储层的岩石物理评价,对于当前碳酸盐岩和火成岩以及变质岩储层评价具有明显的指导意义.     

分离线圈地面核磁共振找水正演

分离线圈地面核磁共振找水方法是将激发线圈与接收线圈分离开来的找水探测方法.文中阐释分离线圈地面核磁共振找水方法正演表达式;利用高斯积分方法计算了分离线圈正演公式中的核函数.通过分析核函数的变化规律,得出分离线圈地面核磁共振方法具有较高的横向分辨率.通过计算全空间的核函数矩阵,将地下含水模型离散化,实现分离线圈地面核磁共振找水3D模型正演快速计算.通过对比计算1D含水模型响应,本文的计算选取网格的越小,正演精度越高.文中计算装置对模型的响应,分析正演曲线随着模型的埋深与装置的不同呈现的变化规律,研究分离线圈地面核磁共振的分辨特性及探测特点.     

多极子声波测井在低孔低渗气层中的数值研究

现有的天然气勘探中的测井技术,在评价低孔低渗气层时遇到诸多难题,本文引入了一种新的气藏评价方法,即利用多极源激发的模式波的幅度来识别气藏,并对此方法进行了数值验证.以Biot多孔介质理论为基础建立了低孔低渗含气储层计算模型,数值计算了多极子声源在充液井孔中激发的频散曲线、衰减曲线以及全波列波形.结果表明,挠曲波和螺旋波的衰减系数与相速度相比,对孔隙中的流体性质更敏感,且随着多极源级数的增加和工作主频的提高,挠曲波和螺旋波的衰减系数的变化程度明显增强;在偶极子和四极子激发的全波列波形中,可清晰的观测到对地层孔隙流体不敏感的地层横波,在这种情况下,可以通过对比波列中地层横波和频散的弯曲波(或螺旋波)幅度来识别气层.     

核磁共振与瞬变电磁三维联合解释方法

传统核磁共振地下含水量解释多采用基于均匀半空间或层状导电模型的一维反演, 分层给出地下含水信息.然而, 这些方法忽略了地下复杂电阻率分布信息对结果的影响, 也不能很好地反映局部三维含水构造.本文从三维电介质中核磁共振响应的正演理论出发, 提出首先利用瞬变电磁数据进行基于等效导电平面法的快速电阻率成像, 然后将成像结果作为核磁共振三维反演的电性模型, 进行联合解释.激发磁场的分布采用有限元法直接求解, 通过引入伪δ源实现电流源的加载, 并强加散度条件排除了三维磁场模拟中"弱解"的影响.针对核磁共振灵敏度矩阵的病态性和数据中存在的干扰信号, 提出考虑罚项的非线性拟合目标函数, 利用线性化方法进行核磁共振反演.模型数据表明该方法能较准确反映地下三维含水构造, 实测算例进一步证明了方法的有效性.本研究将促使核磁共振方法在岩溶、裂隙水、孤立水体等复杂水文地质条件及隧道、矿井灾害水源探测等方面得到有效应用.     

核磁共振找水技术的研究现状与发展趋势

近20多年来,用核磁共振(Nuclear Magnetic Resonance,NMR)方法形成的一种直接非侵害性的探测地下水的地球物理新技术,与传统的地球物理探测地下水的方法相比具有高分辨力、高效率、信息量丰富和解的唯一性等优点,是一种很有发展前景的找水方法技术.我国的水资源短缺,对地下水资源的勘探、开发与利用十分重视,已将核磁共振找水技术研究列入国家十一五科技支撑计划.本文在广泛收集迄今为止的国内外大量资料的基础上,并根据作者近年来有关核磁共振找水技术的研究经历,综述了核磁共振找水技术的发展历史、现状和发展趋势,以推进我国核磁共振找水技术的发展.     

火山岩、白云岩储层基质孔隙度计算方法分析(英文)

火山岩、风化壳白云岩等缝洞储层基质孔隙度计算是测井评价亟需解决的难题之一.本文首先将全直径流纹岩声波实验公式(2005年,李宁)与国内外常用的基质孔隙度计算公式进行了细致的对比;进而就该公式在中基性火山岩、风化壳白云岩等缝洞储层中的适用性进行了深入讨论,并以岩心分析资料为基础,详细给出了该公式与其它公式在计算上述储层基质孔隙度时的误筹分布.误差统计结果表明该公式具有更高的精度.通过中国东部和西部三家油田70口井的实际应用验证,在孔隙度从1.5%到15%范围内,该公式不仅适用于酸性火山岩储层,而且适用于中基性火山岩、风化壳白云岩等缝洞储层基质孔隙度的评价.同时,该公式能够最大限度地减小扩径、岩石蚀变等复杂地质条件对计算结果的影响,实用性更强.     

Understanding the effect of elliptical polarization in surface nuclear magnetic resonance method

Currently, surface nuclear magnetic resonance (SNMR) method is the only geophysical method that detects groundwater directly. In this paper, we investigate the effect of elliptical polarization in the perpendicular excitation magnetic field. The effect of elliptical polarization is clearly visible in our ellipticity calculation and it can cause strong distortion to the excitation field in the presence of high subsurface conductivities. By examining the co-rotating and counter-rotating components of the field, we show that elliptical polarization affects transmitting and receiving processes differently and that a clear phase lag exists between transmitter loop and receiver loop. Finally, we derive the response function of coincident loops and calculate proton tip angles, the kernel function and SNMR response curves of a 1D aquifer model. Based on the simulations, we conclude that the elliptical polarization and phase lag can significantly affect SNMR response and it is essential to include elliptical polarization in SNMR modeling and data interpretation.     

利用成像测井自动判别礁滩储层沉积相和岩性

礁滩储层是我国海相碳酸盐岩油气勘探的重要目标,也是我国油气产能的重要接替领域之一。由于礁滩储层储集空间类型多样,非均质性极强,依靠常规测井判别其沉积相和岩性非常困难。成像测井能够清晰地反映礁滩储层的结构组分和沉积构造,为沉积相和岩性的判别提供了可靠的依据。在对大量礁滩储层的成像和岩心对比观察的基础上,我们提出了9种典型的成像解释模式,建立了利用成像解释模式自动判别礁滩储层沉积相和岩性的方法并研制了相应的处理软件。该方法在塔中和川东北地区礁滩储层的实际应用中取得了良好的效果。     

导电性影响的地面核磁共振反演

导电性影响对实际的地面核磁共振反演非常重要. 在导电条件下,导出了地面核磁共振感应电动势的平方是含水率分布的二次型. 通过进一步分析,我们将其对含水率的灵敏度用显式表示出来,为由核磁感应电动势利用迭代技术快速求解含水率分布奠定了理论基础. 数值模拟结果表明,在自由空间与导电条件下,采用非线性反演技术获得的含水率分布与理论模型都有非常好的一致性.     

基于半监督学习的井震联合储层横向孔隙度预测方法

传统地震储层预测技术一般基于弹性参数反演和岩石物理建模的级联流程实现储层孔隙度预测, 其预测精度受到波动理论和岩石物理理论的近似假设、初始模型和二次反演累积误差等因素的影响.为缓解这些问题, 本文提出了一种基于双向门控递归单元神经网络的半监督学习井震联合孔隙度预测方法, 实现从地震数据直接预测储层横向孔隙度.通过少量的地震测井样本标签对和多目标函数约束建立智能化多尺度多信息融合孔隙度预测模型, 实现地震数据到孔隙度, 孔隙度再到生成地震数据的闭环映射.此外, 在网络模型每次迭代更新的过程中随机引入非井旁地震道参与网络训练, 非井旁地震道的波形匹配能在一定程度上保证井间孔隙度的预测精度.模型数据和实际数据测试结果表明, 本文提出的方法相比于有监督学习孔隙度预测方法能进一步提高储层孔隙度的预测准确性和横向连续性, 获得较为可靠的储层物性参数的空间分布.

     

基于稀疏表示的地面磁共振信号提取方法

在多孔隙含水层中地面磁共振（surface nuclear magnetic resonance,SNMR）信号呈现多弛豫衰减特性,常规盲源分离方法和单指数拟合方法引起信号严重失真和信息缺失等问题.本文提出了基于稀疏表示的随机噪声背景下多弛豫SNMR信号的提取方法.根据SNMR信号的衰减特征,设计了精确刻画SNMR信号且与随机噪声不相关的离散衰减余弦冗余字典.其次,针对多弛豫SNMR信号稀疏度未知的问题,通过设置合理的残差比阈值控制迭代次数,改进了广义正交匹配追踪（generalized orthogonal matching pursuit,gOMP）算法,使得该方法应用于SNMR信号的提取时,具有更好的自适应性和普适性.再次,鉴于SNMR测量数据为多次独立重复采集的结果,提出了基于数据流的SNMR信号提取策略,在提高算法鲁棒性的同时,保证了信号提取结果的唯一性.最后,通过仿真和实测数据证明了基于gOMP算法的稀疏表示方法可以显著地提升多弛豫SNMR信号的提取质量,降低随机噪声对含水层反演结果的影响,提高SNMR探测能力.

     

Advanced characterization of pores and fractures in coals by nuclear magnetic resonance and X-ray computed tomography

This paper demonstrates capabilities of low-field nuclear magnetic resonance (NMR) and microfocus X-ray computed tomography (μCT) in advanced, nondestructive, and quantitative characterization of pore types, producible porosity, pore structure, and spatial disposition of pore-fractures in coals. Results show that the NMR transverse relaxation time (T2) at 0.5–2.5, 20–50, and >100 ms correspond to pores of <0.1 μm, >0.1 μm, and fractures, respectively. A much higher T2 spectrum peak reflects a much better de...     

Petrophysical evaluation and its application to AVO based on conventional and CMR-MDT logs

常规测井为 AVO 分析提供了基础的资料, 成为联系岩石物理与地震资料的桥梁。然而如果储层存在有复杂的流体系统, 如地层被严重地层流体侵入、电阻率响应低及盐水矿化度复杂等的现象, 则常规测井无法提供高质量的测井资料, 导致得出错误的弹性计算结果, 使 AVO 结果与地震资料不吻合。中国渤海湾地区第三系裂缝性储层复杂, 我们利用常规测井和核磁共振测井与模块地层动态测试相结合的组合仪完成了地层评价和储层描述。研究结果表明岩石物理学家利用上述方法技术可以获得诸如空隙度、渗透率、含水饱和度、束缚流体以及空隙压力等重要的储层参数并进一步综合应用这些结果和以实验室测量数据为基础的岩性分析结果进行在地震域岩石物理研究和 AVO 分析。