围压条件下岩石的抗拉强度

用水压致裂法对7种岩石的厚壁圆筒试件进行不同围压下的抗拉强度实验,并从试件致裂瞬间的内壁环向应力σt,环向应变εt等五种参数随围压变化的角度,对围压条件下岩石的抗拉强度进行研究。结果表明,若用σt表示岩石的应力抗拉强度,则σt随围压的增加而减少,并由低围压时的拉应力逐渐过渡为高围压时的压应力。高围压时,虽然试件已处于三向受压状态,但其破裂仍表现为典型的张性破裂。从另一意义上讲,处于高围压环境中的岩石,其内部不可能存在拉应力,拉应力只在低围压状态中存在。若岩石的应变抗拉强度由εt表示,即使岩石三向受压,张性破裂的εt始终是拉应变,岩石的抗拉强度由应变来表征似乎更合理。εt先随围压的增大而增大,当围压超过某一特征值后,εt反随围压的增大而有所减少。 将上述结果应用于岩体(或地震)破裂,可以证明,当岩体内存在σ_3<μ(σ_1+σ_2)的应力状态时,即使三向受压,岩体照样会出现张性破裂。由此认为,地震的震源也存在着张性破裂的可能。     

压力及流体对岩石孔隙结构与黏弹性的影响规律研究:理论模型及实验观测

地质成因和构造/热应力导致地壳岩石中的孔隙结构（裂隙和粒间孔）的变化.影响岩石黏弹性的因素包括压力、孔隙度、孔隙中包含的流体和孔隙几何形状等.相对于岩石中的硬孔隙,岩石黏弹性（衰减和频散）受软孔隙（裂隙）的影响更大.本文选取三块白云岩样本,进行了不同围压和流体条件下的超声波实验测量.利用CPEM（Cracks and Pores Effective Medium,裂隙和孔隙有效介质）模型获得了岩石高、低频极限的弹性模量,并通过Zener体（标准线性体）模型将CPEM模型拓展到全频带而得到CPEM-Zener模型,用该模型拟合岩石松弛和非松弛状态下的实验数据,本文得到平均裂隙纵横比和裂隙孔隙度以及纵波速度和品质因子随频率的变化关系.结果表明,饱水岩石的平均裂隙纵横比和裂隙孔隙度均高于饱油岩石,随着压差（围压和孔隙压力的差值）的增加,饱油岩石中的裂隙首先闭合.并且压差在70 MPa以内时,随着压差增大,岩石的平均裂隙纵横比和裂隙孔隙度在饱水和饱油时的差值增大,此时流体类型对于岩石裂隙的影响越来越显著,此外,对饱水岩石,平均裂隙纵横比随压差增加而增大,这可能是由于岩石中纵横比较小的裂隙会随压差增大而逐渐趋于闭合.在饱水和饱油岩石中,裂隙孔隙度和裂隙密度都随着压差增加而减小.通过对裂隙密度和压差的关系进行指数拟合,本文获得压差趋于0时的裂隙密度,且裂隙密度随孔隙度增大而增大,增大速率随压差增加而降低.针对饱水和饱油的白云岩样本,CPEM-Zener模型预测的纵波频散随压差增大而减小,此变化趋势和实验测得的逆品质因子随压差的变化关系基本一致,由此进一步验证了模型的实用性.本研究对岩石的孔隙结构和黏弹性分析以及声波测井、地震勘探的现场应用有指导意义.     

静水条件下砂岩渗透性的试验研究

在TRIAXIAL CELL V3岩石三轴伺服试验机上进行了砂岩的渗透试验,采用流量法测量不同围压和渗透压作用下的砂岩渗透率,揭示了围压和渗透压对砂岩渗透率的影响规律,并给出了围压与渗透率的拟合关系式。结果表明,在相同围压下,随着渗透压差的增加,砂岩渗透率呈不同程度的增加;围压越小,渗透压差对渗透率的影响越大;当渗透压差相同时,砂岩围压一渗透率曲线变化趋势基本一致,渗透率随围压的增加而减小,显示砂岩内部裂隙的闭合程度受围压的影响较明显。     

水渗透引起的应力场调整及岩石强度弱化的初步研究

本文采用二维线弹性的两相多孔介质理论,对水库蓄水后由水渗透引起的耦合应力变化及岩石强度弱化进行了数值模拟计算。结果表明,由于水的渗透使得岩石中的孔隙压力增大,耦合应力随之减小,从而导致岩石的有效应力减小,同时抗剪强度也相应减小,其减小的量值可以与地震时断层面上的应力降相比。根据计算结果,本文讨论了由水渗透引起地震的可能机制。     

储层温压变化与油藏地震监测

在分析储层温压变化对孔隙流体地震特性、岩石孔隙度和速度等影哈的基础上，以油藏注水地震监到为例说明了油藏地震监剩中考虑温压变化的重要性。研究结果表明：①储层温度、压力的变化将会引起原油地震特性的明显变化，但地层水的变化相对较小。②温度对岩石孔隙度和速度的影响是线性的，而压力的影响则是非线性的。对于中等孔隙的砂岩，温度每增加20℃，岩石的孔隙度和纵横波速度分别减小约2.6％和1.0％以上。对于深度在1100m左右的储层，4MPa的地层压力降低将分别会引起约1.8％和3.3％的纵、横波速度增加。③在油藏强化开采地震监副研究中，除流体替换外，当储层温度、压力的变化较大时，其对实施油藏地震监测有具有非常重要的影响，必须慎重对待。     

围压对低渗砂岩渗透率有效应力系数的影响

多孔岩石渗透率有效应力系数的取值至今仍没有一致的认识,影响取值的因素较为复杂.为了探索围压对低渗砂岩渗透率有效应力系数的影响,实验上采用较大的围压范围(10MPa～50MPa),选取两块低渗致密砂岩岩样,进行渗透率测试,并利用二元线性回归方法,计算了不同围压组合下的渗透率有效应力系数值,获取了该系数随围压的变化趋势.实验中,两块岩样的渗透率有效应力系数随围压的增加而减小,但各自的减小趋势略有不同.利用Bernabé和Berryman提出的模型,理论上解释了围压对渗透率有效应力系数的影响,并得到渗透率有效应力系数的下限值为岩样孔隙度.尽管渗透率有效应力系数不是一个常数,但可以表示为压差的函数,进而起到简化分析的作用.     

岩石三轴压缩实验的强度特性及应用

结合实例对岩石三轴实验数据的一些主要特点和适合应用的领域进行了探讨。结果为:①岩石的三轴抗压、抗剪强度随围压(或深度)的增大而增大。低围压时,呈线性增大;当围压超过某一值后,变为增长率逐渐下降的非线性增大;至更高围压后,抗压强度与围压的应力差、抗剪强度将趋于某一常数。②岩石的单轴强度是强度中的极小值。工程应用中应采用三轴强度,以降低造价、避免浪费。③在现有的各种岩石力学实验方法中,三轴实验得出的凝聚力C和内摩擦角Φ相对最准确。④岩石三轴实验数据在与地学相关的领域内有着广泛的用途。     

塔巴庙低渗致密砂岩渗透率有效应力定律实验研究

为了从实验角度探索低渗砂岩是否存在很小的ESCK值及重新认识低渗砂岩ESCK的变化规律,用两种修正的析因设计方案开展了塔巴庙低渗致密砂岩渗透率有效应力定律实验研究.一种方案包含了3个循环,每个循环是在孔隙流体压力不变,通过加载和卸载围压完成的;另一种方案包含4个循环,每个循环是在围压不变,通过降低和增加孔隙流体压力完成的.采用稳态法采集每个测点的渗透率值,并选择合适的经验模型拟合实验数据.为了使模型更好地拟合实验数据,本文采用最大似然函数法确定的转换系数转换实验得到的渗透率数据,使拟合得到的经验模型计算的渗透率值与实验值偏差的联合概率密度趋于极大值且残余平方和最小.拟合得到的经验模型可以用渗透率-围压-内压响应面直观地表示,再用Bernabe的ESCK计算式将这一响应面转换成渗透率有效应力系数ESCK-围压-内压响应面.ESCK响应面的响应特征表明,ESCK随围压和孔隙流体压力的变化而变化,随围压的增加而降低,随内压的增加而增加,反之亦然;实验研究还表明,ESCK的变化范围在0.0~1.02之间,这一变化范围和以往实验的结果存在巨大的差异,为此,文中分析了产生这一差异原因,同时提出一新的机理模型解释了实验获取的ESCK的变化规律是低渗岩石中微裂缝和孔隙变形共同作用的结果.     

西昌昔格达组黏土岩动力特性试验研究

在大量动三轴试验的基础上,研究了不同固结条件(σ3c=100,200,400 kPa,kc=1.0,1.5,2.0)下西昌昔格达组黏土岩的动应力-动应变关系、动弹性模量、阻尼比及动强度特性。研究结果表明:西昌昔格达组黏土岩在一定条件下的动应力-动应变关系符合幂函数模型。动应力随着固结围压σ3c或固结主压力比kc增大而增大。在相同围压下,达到相同动应变时,偏压固结状态比均压状态所需要的动应力大。当其他条件相同时,动弹性模量随固结压力或固结主压力比增大而增大,随着动应变的增加而减小并趋于稳定。最大动弹性模量Ed0与σ3c/Pa、kc均有良好的幂函数关系,且对不同固结应力状态条件可以归一。阻尼比随动应变增大而增大,但增大幅度随动应变增大而迅速减小,阻尼比随围压或固结主压力比增大而减小,但它们对阻尼比影响较小。不同固结应力状态下(λ/λmax)与(1-Ed/Ed0)有良好的幂函数关系。西昌昔格达组饱和黏土岩动剪应力τd随固结围压σ3c或固结主压力比kc增大而增大,随振动次数增加而减小。τd/σm均随固结围压σ3c增大而减小,随固结压力比kc增大而增大。动剪应力τd与平均压力σm、固结主压力比kc有较好的线性关系。     

固原重塑黄土动力特性共振柱试验研究

利用GCTS共振柱测试仪研究了干密度和固结压力对固原黄土重塑土动剪切模量和阻尼比的影响及试验数据误差的基本规律。通过设计不同工况的试验条件,对比分析结果表明:相同含水率条件下,最大动剪切模量G_(dmax)随固结压力和干密度的增大而增大。相同干密度条件下,黄土的动剪切模量比随围压的增大而增大;阻尼比随围压的增大而减小;相同围压条件下,黄土动剪切模量比随干密度的增大而增大,阻尼比随干密度的增大而减小;不同剪应变特征点的动剪切模量比和阻尼比试验数据呈现一定的离散性,且离散程度阻尼比明显高于动剪切模量比。研究成果可为该地区场地地震反应分析及工程建设提供基础资料。     

地质流体活动的形变场响应研究进展

地球内部流体储层的体积变化可以直接导致地球介质的变形。通过地表形变场的研究可以实现对地球内部储集体的动态监测，同时，还可以获取储层的有关性质。本文综述了当前利用地表形变测量研究石油开采诱发地震响应、地热开采导致陆地下沉、岩浆的侵入引起的地表抬升等地质现象的几种方法。油田开发过程的系列研究成果说明，地面形变测量研究是研究地球内部流体储层体变化过程的有效手段之一。     

Improved normalization of time‐lapse seismic data using normalized root mean square repeatability data to improve automatic production and seismic history matching in the Nelson field

Updating of reservoir models by history matching of 4D seismic data along with production data gives us a better understanding of changes to the reservoir, reduces risk in forecasting and leads to better management decisions. This process of seismic history matching requires an accurate representation of predicted and observed data so that they can be compared quantitatively when using automated inversion. Observed seismic data is often obtained as a relative measure of the reservoir state or its change, however. The data, usually attribute maps, need to be calibrated to be compared to predictions. In this paper we describe an alternative approach where we normalize the data by scaling to the model data in regions where predictions are good. To remove measurements of high uncertainty and make normalization more effective, we use a measure of repeatability of the monitor surveys to filter the observed time‐lapse data. We apply this approach to the Nelson field. We normalize the 4D signature based on deriving a least squares regression equation between the observed and synthetic data which consist of attributes representing measured acoustic impedances and predictions from the model. Two regression equations are derived as part of the analysis. For one, the whole 4D signature map of the reservoir is used while in the second, 4D seismic data is used from the vicinity of wells with a good production match. The repeatability of time‐lapse seismic data is assessed using the normalized root mean square of measurements outside of the reservoir. Where normalized root mean square is high, observations and predictions are ignored. Net: gross and permeability are modified to improve the match. The best results are obtained by using the normalized root mean square filtered maps of the 4D signature which better constrain normalization. The misfit of the first six years of history data is reduced by 55 per cent while the forecast of the following three years is reduced by 29 per cent. The well based normalization uses fewer data when repeatability is used as a filter and the result is poorer. The value of seismic data is demonstrated from production matching only where the history and forecast misfit reductions are 45% and 20% respectively while the seismic misfit increases by 5%. In the best case using seismic data, it dropped by 6%. We conclude that normalization with repeatability based filtering is a useful approach in the absence of full calibration and improves the reliability of seismic data.     

RESERVOIR CAPACITY DEPLETION ON ACCOUNT OF SEDIMENTATION

l 1NTRODUCTIONAs the sediment cAned by the river gets dePositOd in the reservoir, there is a pro gressive reduction in itscaPacity to hold water. For examPle the Zuni reservoir on river Zuni, a tributary of the little ColoradO atBlack rock, New Mexico, U.S.A., lost aboat 75% caPacity in just 20 years. Sindlary, just in l0 years theIchari reservoir on river Tons, a tribUtary of river Yamuna (Inda), reduced to about l5% of its originalcaPacity. Thus, at the planning stage, one must …     

Reservoir rehabilitation: The new methodological approach of Economic Environmental Defence

This paper proposes a new methodological approach to silted reservoir management and defence, which combines the reservoir rehabilitation process and the utilization of the recovered water volumes and sediments. This approach, strategic from both the economical and environmental points of view, is here defined as Economic Environmental Defence (EED) of a reservoir. The EED approach is applied to the case study of Guardialfiera reservoir, where the available experimental data allowed the estimation of silta-tion up to date, the analysis of the distribution of sediment particle size along the reservoir bottom and the possibility to propose a feasible utilization of water and sediments resulting from the reservoir rehabilitation.     

Analysis of reservoir heterogeneity-induced amplification effect on time-lapse seismic responses of fluid substitution: A physical modelling study

Seismic wave propagation through a fluid-saturated poroelastic layer might be strongly affected by media heterogeneities. Via incorporating controlled laboratory simulation experiments, we extend previous studies of time-lapse seismic effects to evaluate the wave scattering influence of the heterogeneous nature of porous permeable media and the associated amplification effects on 4D seismic response characteristics of reservoir fluid substitution. A physical model consisted of stratified thin layers of shale and porous sandstone reservoir with rock heterogeneities was built based on the geological data of a real hydrocarbon-saturated reservoir in Northeast China. Multi-surveys data of good quality were acquired by filling poroelastic reservoir layers with gas, water and oil in sequence. Experimental observations show that reservoir heterogeneity effect causes significantly magnified abnormal responses to the fluid-saturated media. Specifically, reflection signatures of the gas-filled reservoir are dramatically deviated from those of the liquid fluid-filled reservoir, compared with ones of the homogeneous media. By removing the influences unrelated to reservoir property alterations, 4D seismic estimates of travel-time and frequency-dependent characteristic are reasonably consistent with fluid variations. Nevertheless, strong 4D amplitude difference anomalies might not correspond to the regions where fluid variations occur. We also find that 4D seismic difference attributes are evident between oil- and water-filled models, whereas significant between oil- and gas-filled models. Meanwhile, rock physics modelling results reveal the predicted 4D seismic differences are obviously smaller than those calculated from seismic observations. The results in this paper, therefore, implicate that the effect of a reservoir's heterogeneous nature might be beneficial for hydrocarbons detection as well as monitoring small variations in pore fluids.     

A land controlled‐source electromagnetic experiment using a deep vertical electric dipole: experimental settings,processing, and first data interpretation

A multichannel borehole‐to‐surface controlled‐source electromagnetic experiment was carried out at the onshore CO₂ storage site of Hontomín (Spain). The electromagnetic source consisted of a vertical electric dipole located 1.5 km deep, and the electric field was measured at the surface. The subsurface response has been obtained by calculating the transfer function between the transmitted signal and the electric field at the receiver positions. The dataset has been processed using a fast processing methodology, appropriate to be applied on controlled‐source electromagnetics (CSEM) data with a large signal‐to‐noise ratio. The dataset has been analysed in terms of data quality and repeatability errors, showing data with low experimental errors and good repeatability. We evaluate if the induction of current along the casing of the injection well can reproduce the behaviour of the experimental data.     

基于逆建模理论的储层特征定量预测方法

定量描述储层特征的物理量称为储层参数,在储层描述工作中储层参数预测是一个重要环节.本文以岩石物理理论为基础研究了利用岩石物理逆建模理论进行储层参数预测的方法.在合理、有效的岩石物理模型的基础上,逆建模方法通过弹性参数的等值面的空间交会可以预测出储层参数.在此基础上提出了一种扩展的岩石物理逆建模方法,在两个不同的储层参数域进行三维岩石物理逆建模,通过逆建模结果的参数域转换可以预测更多的储层参数,为储层特征描述提供了更加充分的数据支持.输入数据的种类对于预测结果的准确性有较大影响,利用本文建立的弹性参数适用性分析方法可以选择出适用性好的弹性参数组合作为输入数据.将本方法应用于模型数据和实际工区数据,取得了较好的预测效果,证明方法具有一定的实用性.     

EXTREME RESERVOIR SEDIMENTATION IN AUSTRALIA:A REVIEW

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蘑菇湖水库富营养化发生机制和治理途径的探讨

通过对蘑菇湖水库的水质、底质和水生生物等的调查,分析了该水库富营养化的发生机理,并对恢复生态平衡、防治富营养化的途径进行了探讨。