地洼盆地砂岩铜矿床的构造-流体-成矿体系及演化

我国南方地洼盆地构造演化、流体演化和砂岩铜矿成矿作用三者之间具有密切的关系,处于一个统一的系统之中。盆地早中期的裂陷、坳陷作用及热构造活动导致了富铜矿源层的形成、大气降水的深循环和水／岩相互作用、并形成中高温、压、高盐度的热卤水含铜流体。在构造－流体－砂岩铜矿成矿体系的演化中,构造演化制约了含铜流体的演化和砂岩铜矿的成矿作用,而主要发生于盆地演化的晚期。     

低渗透压力条件下砂岩渗透性质的CT试验

运用岩石高压三轴加载装置和渗透压加载装置,对砂岩进行固定应力变渗透水压力试验,同时借助SOMATOMPLUS螺旋CT扫描机进行实时观测。通过试验结果分析,推出了基于CT数的岩石空隙率公式,从CT尺度上分析了岩石空隙率、渗透速度、渗流速度、微孔隙直径、渗透率等随渗透水压力的变化规律。结果表明:岩石的渗透参数随渗透压力的增加而增大,渗透参数随渗透压力的变化呈对数关系,这是由于渗透水压力使岩石内部空隙发生变形,这一变形为弹性变形;而渗流速度与渗透水压力呈线性关系,符合宏观尺度渗流的达西定律。      

含流体致密砂岩的纵波频散及衰减:基于双重双重孔隙结构模型描述的特征分析

致密砂岩普遍具有低孔、低渗及微裂缝发育的地质特征,并且呈现出很强的非均匀性.致密砂岩储层与常规砂岩储层比较,具有明显的岩石物理性质、渗流力学性质方面的差异.致密砂岩内部的非均匀性对弹性波频散、衰减有显著影响,其中包括孔隙结构的非均匀性,即岩石内部孔隙参数的不均一性,以及孔隙内部不相混溶流体的非均匀分布;此外,非均匀性的尺度也决定了波出现显著频散与衰减的频段.综合考虑致密砂岩孔隙结构非均匀性及流体斑块状饱和的非均匀性,本文采用双双重孔隙介质结构模拟了致密砂岩的弹性波响应,分析了同时具备两类非均质性岩石中的波传播特征.调查分析了两组分别来自中国鄂尔多斯盆地苏里格气田及四川盆地广安气田的不同类型致密砂岩储层的岩芯超声波实验数据,给出了岩石样本的弹性波速度频散与衰减曲线.结果显示理论模型预测结果与完全饱和、部分饱和岩石的实验数据吻合良好.对两个地区致密砂岩岩芯数据进行对比分析,苏里格致密砂岩样本总体上比广安致密砂岩渗透率高,在各孔隙度范围内,特征模拟显示苏里格样本的裂隙尺寸明显大于广安样本.广安致密砂岩在低孔隙度范围内发育了更多、更小的颗粒裂隙/接触.致密砂岩的速度频散与衰减结果受流体黏度、晶体破裂及流体斑块状饱和的共同影响.此外,孔隙度越大,部分饱和岩石中斑块状饱和机制对总衰减的贡献越低,与之相对,结构非均质性所占的比重则有所增强.     

Characterisation and multifaceted anisotropy assessment of Corvio sandstone for geological CO2 storage studies

We present a comprehensive characterisation of the physical, mineralogical, geomechanical, geophysical, and hydrodynamic properties of Corvio sandstone. This information, together with a detailed assessment of anisotropy, is needed to establish Corvio sandstone as a useful laboratory rock‐testing standard for well‐constrained studies of thermo–hydro–mechanical–chemical coupled phenomena associated with CO₂ storage practices and for geological reservoir studies in general. More than 200 core plugs of Corvio sandstone (38.1 and 50 mm diameters, 2:1 length‐to‐diameter ratio) were used in this characterisation study, with a rock porosity of 21.7 ± 1.2%, dry density 2036 ± 32 kg m^?3, and unconfined compressive and tensile strengths of 41 ± 3.28 and 2.3 ± 0.14 MPa, respectively. Geomechanical tests show that the rock behaves elastically between ～10 and ～18 MPa under unconfined conditions with associated Young's modulus and Poisson's ratio of 11.8 ± 2.8 GPa and 0.34 ± 0.01 GPa, respectively. Permeability abruptly decreases with confining pressure up to ～10 MPa and then stabilises at ～1 mD. Ultrasonic P‐ and S‐wave velocities vary from about 2.8–3.8 km s^?1 and 1.5–2.4 km s^?1, respectively, over confining and differential pressures between 0.1 and 35 MPa, allowing derivation of associated dynamic elastic moduli. Anisotropy was investigated using oriented core plugs for electrical resistivity, elastic wave velocity and attenuation, permeability, and tracer injection tests. Corvio sandstone shows weak transverse isotropy (symmetry axis normal to bedding) of <10% for velocity and <20% for attenuation.     

Effects of fluid displacement pattern on complex electrical impedance in Berea sandstone over frequency range 104–106 Hz

To better understand the effect of fluid distribution on the electric response of rocks saturated with oil and brine, we conducted experimental studies on the complex electrical impedance in a Berea sandstone, together with in situ acquisitions of oil distribution images employing a high‐resolution medical X‐ray computed tomography. We performed two tests of brine displacement by oil under high (10 MPa) and low (5 MPa) pressures, which were accompanied by fingering and stable displacement patterns, respectively. The measured complex impedance data were fitted to the Cole model to obtain the resistance, capacitance, peak frequency of the imaginary impedance, and the exponent α of the rock–fluid system. With increasing oil saturation, the resistance showed an increasing trend, whereas the other three parameters decreased. The fingering displacement exhibited lower resistance and capacitance than the stable displacement. The analysis of the resistance changes using a simple parallel connection model indicates that there are more components of residual brine in parallel connections in the fingering pattern than in the stable displacement pattern at the same saturation. We also interpreted the normalised changes in the capacitance (or apparent dielectric constant) with respect to the oil saturation via an analysis of the shape factor of fluid distribution based on the Maxwell–Wagner–Brugermann–Hanai model. The changes in the shape factor suggest that the pinch‐off of the brine in parallel connection by the oil is a dominant mechanism reducing the capacitance. In the stable displacement, most of the connections in the brine phase are immediately pinched off by oil displacement front at a local oil saturation of 65%. Conversely, in the fingering displacement, there is a transition from the bulk or layered brine to the pinched‐off at a local oil saturation below 60%. The analyses indicate that the difference in the fluid distribution under different fluid conditions is responsible for the non‐Archie behaviour.     

热处理砂岩微观结构及力学性质试验研究

采用核磁共振、电镜扫描、X射线衍射、单轴压缩等试验手段对某砂岩试样不同温度下（25～900 ℃）微观结构及力学性质的变化情况进行研究。研究表明：温度对砂岩试样微观结构具有重要影响,试样总孔隙率随温度的升高而升高,在150 ℃以下,由于中、大孔隙的减少,试样渗透性反而降低;当温度超过600 ℃时,中、大孔隙快速增加,试样渗透性能大幅增加;温度升高导致砂岩试样弹性模量减小、峰值应变增大以及孔隙压密阶段变长,宏观表现为脆性降低、塑性明显增强;热处理条件下,除微观结构的变化会导致砂岩试样力学强度改变外,试样矿物成分对其力学强度也具有十分重要的影响;450 ℃以下,由于矿物成分变化较小,试样力学强度主要受到孔隙度增加的影响,表现为强度随温度升高而降低;450～600 ℃,虽然孔隙率继续增长,但由于主要矿物高岭石发生脱水以及与其他离子形成新相矿物,进而导致试样强度没有随着孔隙增加而降低,反而出现一定的增长;超过600 ℃后,孔隙尤其是大孔隙的急剧增加,导致强度重新开始降低。     

Petrological features of a Numidian section in the Lucanian Apennine (southern Italy)

A continuous section of Numidian sandstones cropping out along the eastern margin of the Lucanian Apennine (southern Italy) has been studied in relation to its petrographic and geochemical aspects. Owing to their simple mineralogy, both chemical and petrographic classifications indicate that the sandstones are subarkoses. They are characterized by high mineralogical maturity, poor sorting, abundant siliciclastic matrix and subangular quartz grains. The principal composition is Q_80–94 F_6–20 L_0–1 corresponding to SiO₂/Al₂O₃ and Fe₂O₃/K₂O ratios ranging from 37·216 to 17·124 and from 1·182 to 0·514 respectively. Two quartz grain types were distinguished: deformed and undeformed quartz grains, the former generally subangular in shape and the latter rounded. Two distinct origins of detritus can be suggested; (i) the undeformed and rounded quartz grains derive from arenaceous continental sequences; (ii) the siliciclastic matrix, the deformed subangular quartz grains, the heavy minerals and the large crystals of K-feldspar probably derive from a crystalline basement formed by low–medium–high grade metamorphic rocks and granitoids. The Numidian subarkoses represent the mixing of these two components. Both kinds of detritus can be referred to the African Craton where crystalline basement is extensively overlain by Palaeozoic and Mesozoic sandstones. The different proportions of the two components in the mixture account for the variability of the sandstone composition and might explain the mixed Numidian successions cropping out in various sectors of the Mediterranean area. Copyright © 1998 John Wiley & Sons, Ltd.     

河北武城凸起地热田地热地质特征

在“雄县模式”和环境压力的双重驱动下,河北地区已形成我国最大的地热供暖城市群。因此,研究武城凸起地热田地热地质特征,对河北省故城县地热开发具有重要的指导意义。本文通过测井、地震和区域地质资料,结合水化学特征、同位素测试结果的分析,系统分析了地热田的不同类型热储展布、储集层物性、地下热水补给来源和循环路径特征,并精细评价了地热资源量。结果表明武城凸起地热田热储类型主要为馆陶组砂岩热储和奥陶系岩溶热储。砂岩热储区域稳定分布,主要产水层为下馆陶组,底板埋深1 200~1 600 m,单井出水量79~123 m³/h, 井口水温52~54 ℃;岩溶热储有利区带主要分布在寒武—三叠系卷入的背斜核部,呈南北向带状展布,主要产水层为上马家沟组、下马家沟组和亮甲山组,顶板埋深2 100~2 900 m,单井出水量75~98 m³/h,井口水温82~85 ℃。地下热水来源为西部太行山脉和北部燕山山脉,热水沿着NE-SW向断裂破碎带和岩溶不整合面向上水平运移进入浅层热储,通过沧县隆起和邢衡隆起在武城凸起汇集,形成中低温地热田。地下热水质类型为Cl-Na型,最大循环深度为2 822.5~3 032.5 m,¹⁴C测年表明砂岩热储和岩溶热储年龄分别为21 ka和32 ka。明化镇组和石炭—二叠系分别为两套热储的直接盖层。武城凸起地热田地热资源量分层精细评价结果表明,热储地热资源量合计4.86×10¹⁰ GJ,折合标煤16.6×10⁸ t。年可开采地热资源量可满足供暖面积1.1×10⁸ m²,市场开发潜力巨大。     

松辽盆地北部深层砂岩成岩作用与孔隙演化

松辽盆地北部深层砂岩成岩作用强,原生孔隙保存差。深层砂岩只有出现大量的次生孔隙,才能具有较好的储集性能。本文通过偏光显微镜、扫描电镜和显微热台等分析方法,研究了松辽盆地深层砂岩岩石类型,成岩作用特征和各成岩阶段砂岩孔隙的演化,表明胶结作用是影响深层砂岩储层物性变差的主要原因,浊沸石胶结物的溶解是深部砂岩储集性能得以改善的主要原因。     

Surficial fractures in the Navajo sandstone,south-western USA: the roles of thermal cycles,rainstorms, granular disintegration,and iterative cracking

Deep (> 5 m) sheeting fractures in the Navajo sandstone are evident at numerous sites in southern Utah and derive from tectonic stresses. Strong diurnal thermal cycles are, however, the likely triggers for shallow (< 0.3 m) sheeting fractures. Data from subsurface thermal sensors reveal that large temperature differences between sensors at 2 and 15 cm depth on clear summer afternoons are as great as those that trigger sheeting fractures in exposed California granite. Extensive polygonal patterns in the Navajo sandstone are composed of surface-perpendicular fractures and were produced by contractile stresses. Numerous studies have shown that porewater diminishes the tensile strength of sandstone. Based on our thermal records, we propose that cooling during monsoonal rainstorms triggers polygonal fracturing of temporarily weakened rock. On steep outcrops, polygonal patterns are rectilinear and orthogonal, with T-vertices. Lower-angle slopes host hexagonal patterns (defined by the dominance of Y-vertices). Intermediate patterns with rectangles and hexagons of similar scale are common. We posit that outcropping fractures are advancing downward by iterative steps, and that hexagons on sandstone surfaces (like prismatic columns of basalt) have evolved from ancestral orthogonal polygons of similar scale. In lava flows, fractures elongate intermittently as they follow a steep thermal gradient (the source of stress) as it rapidly moves through the rock mass. In our model, a steep, surficial thermal gradient descends through unfractured sandstone, but at the slow pace of granular disintegration. Through time, as the friable rock on stable slopes erodes, iterative cracking advances into new space. Hexagonal patterns form as new fractures, imperfectly guided by the older ones, propagate in new directions, and vertices drift into a configuration that minimizes the ratio of fracture length to polygon area. © 2020 John Wiley & Sons, Ltd.