Summary. Expressions now exist from which may be calculated the propagation constants of elastic waves travelling through material containing a distribution of cracks. The cracks are randomly distributed in position and may be randomly orientated. The wavelengths involved are assumed to be large compared with the size of the cracks and with their separation distances so that the formulae, based on the mean taken over a statistical ensemble, may reasonably be used to predict the properties of a single sample. The results are valid only for small concentrations of cracks. Explicit expressions, correct to lowest order in the ratio of the crack size to a wavelength, are derived here for the overall elastic parameters and the overall wave speeds and attenuation of elastic waves in cracked materials where the mean crack is circular, and the cracks are either aligned or randomly orientated. The cracks may be empty or filled with solid or fluid material. These results are achieved on the basis of simply the static solution for an ellipsoidal inclusion under stress. The extension to different distributions of orientation or to mixtures of different types of crack is quite straightforward.

The method of smoothing has lead to the calculation of overall or effective elastic parameters for wave propagation in material containing cracks, valid to second order in the number density of the cracks. Wavespeeds are obtained for wavelengths long compared with crack dimensions by working to the lowest order in frequency. To find the attenuation due to scattering of energy out of the mean wave, calculations to higher order in frequency are necessary and, up to now, attenuation has been obtained by summing over the scattering cross-sections of the cracks, thus neglecting any crack-crack interactions. Here we evaluate scattering attenuation to higher order in the series obtained from the smoothing approximation in order to allow for multiple scattering. It turns out that, for crack radii and crack spacing small compared with a wavelength, the term of lowest order taken from the double scattering component exactly cancels out the sum over scattering cross-sections, leaving only higher order terms to account for attenuation due to scattering. In other words, the effective material parameters contain no attenuation component arising from scattering.

Small-scale heterogeneity in crustal structure can be very complex and difficult to describe in detail and yet, at the same time, can be very important for the description of, for instance, tectonic stress and porosity. Statistical properties of such heterogeneity can be derived from the properties of waves of relatively large wavelength as they propagate through the crust. The differences between measured wavelengths and attenuation coefficients and those of compact rock and the variations of these quantities in space and time provide, in principle, a means of determining quantities like the density and orientations of microfractures and the nature of crack infill material. The theoretical basis for inferences of this kind is the concept of the 'effective' or 'equivalent' material based on an averaging process taken over the microstructure. A number of methods have been used to calculate the properties of the effective medium, several of which are described here.

This paper studies the effect on the overall properties of a cracked solid of the existence of connections between otherwise isolated cracks and of small-scale porosity within the 'solid' material. The intention is to provide effective medium models for the calculation of elastic wave propagation with wavelengths greater than the dimensions of the cracks. The method follows that of earlier papers in which the overall elastic properties are directly related to parameters governing the microstructure, such as crack number density and the mean radius and spacing distance of the cracks. Expressions derived by the method of smoothing are evaluated to second order in the number density of cracks, thereby incorporating crack crack interactions through both the strain field in the solid and the flow field of fluids in the pores. Flow of interstitial liquids tends to weaken the material; the limit of zero flow is equivalent to isolating the cracks and the limit of free flow is equivalent to dry (gas-filled) cracks. It also introduces additional attenuation. The inclusion of small-scale porosity gives a model of 'equant porosity' which is more closely constrained by the details of crack dynamics than earlier models.

The E_1s_3~5 member in Tanggu district is a fault block,high-pressure and fractured lacustrine dolostones reservoirs.Based on the core observation,thin sections and log data with Ansys,the authors study on the causes and formation periods of fractures in lacustrine dolostones reservoirs,describe the fracture characteristics and analyze the control factors of fractures.The results show that the fractures are mainly of the tectonic origin,with a few bedding fractures and dissolution fractures,and the seepage ability decreases successively.There are four stages of fractures development including bedding fractures parallel to beddings,oblique fractures with 45 and 60 degrees,tensile fractures with 75 to 90 degrees,and high angel fractures with70 to 85 degrees.The structure,lithology,diagenesis and overpressure are the key control factors of fractures in lacustrine dolomite reservoir,which are obviously influenced by cracks and stress field.The fractures mainly develop near the fault cross zone with 2 groups of NW and NE trending faults,and the above mentioned fracture development zone with high pressure called the sweet spots should be valued in oil-gas exploration.

碳酸岩复杂的孔隙结构和强烈的非均质性,导致传统的阿尔奇模型存在一定不适用性,主要体现在,m,n值的变化范围大.从岩石体积物理模型出发,设定n为常数,扩展m的含义并重新定义为孔隙结构指数,用它代替原Archie公式中胶结指数和饱和度指数对含水饱和度计算的影响.鉴于碳酸盐岩孔隙成因的复杂性和孔隙结构的复杂性,特别是裂缝型和溶蚀孔洞型碳酸盐岩储层取心困难,采用数值模拟手段考察碳酸盐岩孔隙结构指数m的影响因素及变化规律, 主要包括孔隙结构特征参数孔喉比、孔隙度、泥质含量等因素对表征岩石导电性的F和岩石孔隙结构指数m的影响,又通过引入孔隙结构组分建立了变m的饱和度模型.应用效果表明新模型成功解决了四川磨溪溶蚀孔洞型碳酸岩储层水层段自由烃饱和度计算偏高的难题.

This paper presents a development of the use of multi-axial ultrasonic data for the quantification of extrinsic, crack or grain-contact induced elastic anisotropy in core samples with application to a UKCS oil field. An approach for inversion of multi-axial velocity measurements is presented, which extends the previous work by Sayers (2002) for the determination of second- and fourth-order crack density tensors from inversion of multi-axial ultrasonic velocity data. The extensions to the inversion approach provide improved consideration of data uncertainties, by using all available P - and S -wave data and also permit the inclusion of an orthorhombic background anisotropy in the inversion [e.g. due to intrinsic lattice preferred orientation(LPO) effects]. The latter aspect leads to estimates of the extrinsic anisotropy, that is, the quantified crack density tensors, that are 'unpolluted' by the effects of the intrinsic anisotropy, thus permitting extrinsic and intrinsic anisotropies to be distinguished. For the samples considered, the extrinsic crack-induced anisotropy is strong relative to that of the intrinsic LPO effects, and the pre-dominant crack-set is commonly aligned parallel to the depositional fabric (which is generally horizontal). However, the LPO and extrinsic anisotropies are in general aligned, which indicates a linked origin. Furthermore, a strong correlation is observed between the degree of VTI anisotropy and the modal content of micas in the samples, which cannot be explained solely by the LPO effect. In fact, it is shown that increased horizontal (grain parallel) crack densities are associated with higher mica content. These horizontal cracks in the mica-rich samples often show moderate-to-strong variations in crack density with loading that might be detected in situ with non-hyperbolic moveout. Additionally, three samples show significant pressure sensitivity of the vertical crack sets indicating that loading-induced azimuthal anisotropy might also exist in some layers in situ and be detectable using azimuthal AVO type analyses. Analysis of the fourth-order crack density tensor allows insight into the relative sizes of the normal and tangential crack compliances, B N and B T . For one case it is found that B N B T (i.e. the crack-sets are more compliant in compression than in shear). For another sample B N < B T ; this sample had been cleaned prior to the analysis, which appears to facilitate shear in the cracks. This conclusion may have significant implications for the use of analogue samples acquired at the surface where organic products, which lead to the reduced shear compliance, are not present.

随着浅层地裂缝等地质灾害问题精细探测需求的增大,采用初至波速度层析反演技术,可以提供较高精度的浅层速度场的纵横向异常变化,可为识别地裂缝等地质灾害现象提供依据。通常,在采集参数一定的条件下,其反演成像精度受算法、网格类型和剖分尺度的限制,在网格类型不变的条件下,要提高精度就必须加密正反演计算网格,改进算法,从而实现增量而不减速且高精度的效果。文中利用OpenMP的单机多核并行技术,探讨并实现了初至波层析成像并行算法,其中正演部分使用了改进的旅行时线性插值法,针对原有的按列计算,加入了按行计算,充分考虑到来自各方向的射线,使得计算出的旅行时最小,反演部分使用了能迅速稳定收敛的LSQR法以及正则化技术,通过理论和实际资料测试,其收敛速度快,反演结果较好。同时,在加密采样和缩小网格尺度的条件下,与常规串行算法相比,其运算速度和效率有较大提高,与商业软件比较,其运算效率差异不大,但反演结果的精度和可分辨性较好。

Porous solid is in contact with a cracked elastic solid at a plane interface between them. For the presence of vertically aligned microcracks, the elastic solid behaves transversely isotropic to wave propagation. The coefficients of elastic anisotropy depend on the crack density and crack porosity in the medium. A loose bonding is considered between the two solids so that a limiting case could be the welded contact. At the plane interface, the imperfection in welded bonding is represented by tangential slipping and, hence, results in the dissipation of a part of strain energy. Three types of waves propagate in an isotropic fluid-saturated porous medium, which are considered for incidence at the interface. Incidence of a wave results in three reflected waves and two refracted waves. Partition of incident energy among the reflected and refracted waves is studied for each incidence, varying from normal to grazing directions. Numerical example calculates the energy shares of reflected and refracted waves at the plane interface between water-saturated sandstone and basalt. These energy shares are computed and analyzed for different values of crack parameters as well as loose bonding parameter.

震源是油气资源勘探和微地震监测中很重要的部分。为恰当地选择地震波勘探震源、节约野外勘探成本,文中基于加载压力源、剪切源和集中力源的理论公式,通过交错网格有限差分法数值模拟获得震源在各向同性介质中的地震波场图,详细讨论震源激发波的分布特征。通过波的偏振理论,从物理上细致地分析震源产生地震波的机理,与解析解一并验证数值模拟结果。所得结果说明:震源力是数值模拟地震波场的可控性因素;震源在三维裂缝介质中可观测到横波分裂现象;物理分析是很好地解释地震波场分布图的一种验证方法。

利用蒙特卡罗方法建立各种条件下的套管井计算模型,模拟相应的热 中子时间谱,进而计算地层宏观吸收截面.模拟结果表明:地层的宏观吸收截面随着孔隙度和含水饱和度的增加而增加,且源距越小、地层水的矿化度和泥质含量越 高、套管的尺寸越大、仪器越居中、俘获截面越高的岩性地层条件下,地层的宏观吸收截面值也越大;套管壁厚和水泥环对地层宏观吸收截面没有影响,但套管壁越 厚、水泥环厚度越小,热中子总计数越低.利用脉冲中子测井数据确定地层含水饱和度时应对各种影响因素作相应的校正.

The time spectrum of all kinds energy neutrons and thermal neutrons, which resulted from the interaction between the formation and neutrons induced by the pulsed neutron source of the different pulsed width, are simulated by Monte Carlo Neutron-particles code. The time spectrum of thermal neutrons under the conditions of the different porosities, salinities and saturations are simulated. The linear relations between formation macroscopic cross sections and porosity, salinity and saturation are gained by the time spectrums, respectively. The results will lay the foundation for the study of PNN logging.

Abstract We obtained the complete set of dynamic elastic stiffnesses for a suite of "shales" representative of unconventional reservoirs from simultaneously measured P- and S-wave speeds on single prisms specially machined from cores. Static linear compressibilities were concurrently obtained using strain gauges attached to the prism. Regardless of being from static or dynamic measurements, the pressure sensitivity varies strongly with the direction of measurement. Furthermore, the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100%. Compliant cracklike porosity, seen in scanning electron microscope images, controls the elastic properties measured perpendicular to the rock's bedding plane and results in highly nonlinear pressure sensitivity. In contrast, those properties measured parallel to the bedding are nearly insensitive to stress. This anisotropy to the pressure dependency of the strains and moduli further complicates the study of the overall anisotropy of such rocks. This horizontal stress insensitivity has implications for the use of advanced sonic logging techniques for stress direction indication. Finally, we tested the validity of the practice of estimating the fracture pressure gradient (i.e., horizontal stress) using our observed elastic engineering moduli and found that ignoring anisotropy would lead to underestimates of the minimum stress by as much as 90%. Although one could ostensibly obtain better values or the minimum stress if the rock anisotropy is included, we would hope that these results will instead discourage this method of estimating horizontal stress in favor of more reliable techniques. 2016 Society of Exploration Geophysicists. All rights reserved.

This study was undertaken to establish an evaluation method for buried dissolution of carbonate reservoir in the Tahe ( ) Oilfield. Because of the difficulty in tracing the dissolution in geologic record, the precipitation is taken as a useful indicator to presume the dissolution reversed. The fluid inclusions data is a useful tool to identify the precipitation. On the basis of the principle that the temperature data of fluid inclusions captured in the calcite fillings of caves and cracks can reflect the fluid activity time, a total of 256 fluid inclusions samples in 12 drills were collected and analyzed to study their forming time in buried environment in the Tahe Oilfield, Tarim Basin, NW China. Results show that the temperature data of fluid inclusions captured by Ordovician cave and crack fillings accumulated in six intervals, which indicated six stages of fluid activity in the area of study. Meanwhile, it is clear that a different number of temperature intervals was captured in different wells, representing a different number of precipitation distributed in space. According to this conclusion, the buried precipitation trend in late Himalayan stage (the sixth stage) was supposed in space and its effectiveness has been approved by the chemical thermodynamics method. This method was also used in all of the other five stages of fluid activity and the comprehensive trend of the buried precipitation in space for Ordovician strata was evaluated. It shows that more temperature intervals were captured in the southwestern region (wells S76, S79, S65 and S75) and the eastern region (well S69) in the area of study, indicating intensive precipitation and weak dissolution in this area. This evaluation method for buried dissolution is a new attempt and may have important implications for further petroleum exploration in the Tarim Basin.

渤南地区沙三下地层发育非常规油气藏,预测地应力及应力甜点是该类油藏勘探及评价的关键。本文提出的地应力及应力甜点地球物理预测方法结合了前人研究成果,以测井岩石物理参数分析为基础,建立地应力、破裂压力与岩石弹性参数的关系,通过多元线性回归拟合力学计算公式,并以弹性参数反演和多体融合技术为依托,实现了应力场及应力甜点的地震预测。理论研究及钻探结果均表明,渤南洼陷中部及南部的低应力区是油气成藏的优势条带,Ⅰ型和Ⅱ型应力甜点是泥岩裂缝型油藏的主要发育区,且具有页岩油产能。实际应力数据和钻探效果验证了方法的有效性,该方法可为非常规油藏勘探提供参考依据。

The southwest basin is a key to study the origin and development of the South China Sea(SCS).We do not know much about its boundaries,geological history,and the formation of its sea floor because it has a complex and highly re-gional structural background,notable sediment activity,and yet few floor rocks.Here a grano-diorite sample was collected from the southern margin of the southwest basin of the South China Sea.The results indicated that the 40Ar-39Ar ages of biotites in the sample are 110.3卤0.5 Ma,suggesting that they were prod-ucts of magmatic intrusion during the Early Cretaceous period.The sample's geochemistry showed it had high SiO2,K2O,and Al2O3 but low TiO2 levels.Tectonic discriminant diagrams suggested that the sample might represent extrusion-related magmatism,either in an arc or forearc setting in the SCS area and that the sample mainly belonged to the syncollision type,whose formation was related to orogenies.The sample may be part of the main rock that made up the boundaries of rift system.The process of tension cracking was similar to the development of the Red Sea,in which the rifting and sagging occurred in the continental crust.The southwest basin may not be an original ocean,but a rift developed through finite extension on continental crust basement.The oceanic crust came into being when the width and depth of the rift valley reached a certain scale.The granodiorite sample we collected provides a means of determining the boundary of the southwest basin and the clues that may help researchers expand relevant models.It constitutes an important datum regarding the analysis of the formation and development of the SCS.

ABSTRACT During surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers, research on the properties of well diameters and oil and water layers and their relation to acoustic logging rules is essential. Using Hudson's crack theory, we simulated oil and water layers with different well diameters or crack parameters (angle and number density). We found that when the well radius increases from 0.03 m to 0.05 m, the variation ratio of compressional wave amplitude for the oil layer is less than that for the water layer. The difference of Stoneley wave amplitude between the crack parameters (angle and number density) is greater in the case of the water layer than in the case of the oil layer. The response sensitivity of wave energy is greater for the water layer than that for the oil layer. When the well radius increases from 0.05 m to 0.14 m, the maximum excitation intensity for oil layer is greater than that for the water layer. We conclude that the propagation of an elastic wave is affected by medium composition and well diameter, and the influence has certain regularity. These results can guide further reservoir logging field exploration work.