鄂尔多斯盆地麻黄山西区块延长、延安组裂缝成因及期次

裂缝的形成是一个复杂过程,对其成因及期次研究需要通过多方面的资料进行综合分析加以确定.对鄂尔多斯盆地麻黄山西区块裂缝的研究首先选择了相似露头区进行裂缝的野外调查,野外裂缝特征表明:裂缝组系不稳定,受构造变形强度、形态所控制,且构造变形越强,裂缝的发育密度越大;确定了裂缝以构造成因为主.通过研究区23口取心井岩心裂缝观察描述,岩心上裂缝主要以垂直或者高角度斜交张性缝为主,且岩心上裂缝之间的切割、限制及组合关系表明了裂缝期次至少存在2期.最后在野外和岩心裂缝特征、成因及期次认识的基础上,进行了岩石声发射实验、裂缝充填物稳定碳氧同位素分析实验,并结合研究区构造演化背景确定了研究区裂缝形成期次主要有两期,可能分别对应研究区燕山运动二幕和三幕两个构造活动时期.     

Geochemical features and origin of natural gas in heavy oil area of the Western Slope,Songliao Basin,China

The Western Slope of the Songliao Basin is rich in heavy oil resources (>70 × 10⁸ bbl), around which there are shallow gas reservoirs (∼1.0 × 10¹² m³). The gas is dominated by methane with a dryness over 0.99, and the non-hydrocarbon component being overwelmingly nitrogen. Carbon isotope composition of methane and its homologs is depleted in ¹³C, with δ¹³C₁ values being in the range of −55‰ to −75‰, δ¹³C₂ being in the range of −40‰ to −53‰ and δ¹³C₃ being in the range of −30‰ to −42‰, respectively. These values differ significantly from those solution gases source in the Daqing oilfield. This study concludes that heavy oils along the Western Slope were derived from mature source rocks in the Qijia-Gulong Depression, that were biodegraded. The low reservoir temperature (30–50 °C) and low salinity of formation water with neutral to alkaline pH (NaHCO₃) appeared ideal for microbial activity and thus biodegradation. Natural gas along the Western Slope appears mainly to have originated from biodegradation and the formation of heavy oil. This origin is suggested by the heavy δ¹³C of CO₂ (−18.78‰ to 0.95‰) which suggests that the methane was produced via fermentation as the terminal decomposition stage of the oil.     

XFEM-based cohesive zone approach for modeling near-wellbore hydraulic fracture complexity

Near-wellbore fracture tortuosity has important impacts on the productivity of fractured oil and gas wells and the injectivity of CO₂ or solids disposal injectors. Previous models for simulating near-wellbore fracture tortuosity usually assume fracture growth in linear-elastic media, without considering the effects of porous features of the rock. In this paper, a 2D fully coupled model is developed to simulate near-wellbore fracturing using the XFEM-based cohesive segment method. The model takes into account a variety of crucial physical aspects, including fracture extension and turning, fluid flow in the fracture, fluid leak-off through wellbore wall and fracture surfaces, pore fluid flow, and rock deformation. The proposed model was verified against two sets of published experimental results. Numerical examples were carried out to investigate the effects of various parameters on near-wellbore fracture trajectory, injection pressure, and fracture width. Results show that near-wellbore fracture behaviors are not only dependent on rock elastic properties and field stresses, but also greatly influenced by porous properties of the rock, such as permeability and leak-off coefficient. Some field implications were provided based on the simulation results. By overcoming some limitations of the previous models, the proposed model predicts more realistic fracture evolution in the near-wellbore region and provides an attractive tool for design and evaluation of many field operations, for which near-wellbore fracture behaviors play an important role on their successes.

     

Reduced sulfur species in a stratified seawater lake (Rogoznica Lake, Croatia); seasonal variations and argument for organic carriers of reactive sulfur

Over a period of a year, Hg⁰-reactive, total reduced sulfur species (RSS_T), as well as a non-volatile fraction that cannot be gas-stripped at pH ∼2 (RSS_NV), have been measured by voltammetry in a stratified, saline lake. In the hypolimnion, RSS_T is dominated by unusually high (up to 5 mM) dissolved divalent sulfur (S^−II), present as H₂S + HS⁻ and as inorganic polysulfides (H_xS_n^x−2). Less abundant RSS_NV is attributed to dissolved zero-valent sulfur (S⁰) in inorganic polysulfides. Assuming negligible contribution of organic S⁰ species in the hypolimnion, the equilibrium distribution of polysulfide ions is calculated; S₅²⁻ is found to predominate. In the epilimnion, all RSS_T consists of RSS_NV within analytical uncertainty. Through spring and summer, RSS_T and RSS_NV display little vertical or seasonal variation, but they increase dramatically when stratification breaks down in autumn. Based on decay rate, RSS during mixing events is attributed to dissolved S₈ from oxidation of sulfide and decomposition of inorganic polysulfides. This hypothesis quantitatively predicts precipitation of elemental sulfur in a year when colloidal sulfur was observed and predicts no precipitation in a year when it was not observed. Except during mixing events, the entire water column is undersaturated with respect to both rhombic sulfur and biologic sulfur, and the limited variations of RSS exclude hydrophobic and volatile aqueous S₈ as a major species. During such periods, RSS (typically 8 nM) may be associated with organic carbon, perhaps as adsorbed S₈ or as covalently bound polysulfanes or polysulfides. The hypolimnion is viewed as a zero-valent sulfur reactor that creates S⁰-containing, dissolved organic macromolecules during stable stratification periods. Some are sufficiently degradation-resistant and hydrophilic to be dispersed throughout the lake during mixing events, subsequently giving rise to ∼10⁻⁸ M RSS in the oxic water column. Voltammetrically determined RSS in oxic natural waters has often been described as “sulfide” or “metal complexed sulfide”, implying an oxidation state of S^−II; we argue that RSS in oxic Rogoznica Lake waters is mainly S⁰.     

广西大厂锡矿铟的地球化学特征及成因机制初探

广西大厂锡矿位于江南古陆西南缘,桂西北海西-印支期被动陆缘裂谷盆地北部的断裂凹陷盆地中,是中国重要的、以锡为主的有色金属矿床。它主要由长坡-铜坑和高峰矿床、拉么矿床、大福楼矿床和亢马矿床等组成,其铟资源量约6 000 t。文章在对长坡-铜坑矿床、高峰矿床以及拉么矿床不同类型围岩（包括花岗岩质岩石）、矿石以及不同矿床类型中矿石矿物（硫化物和氧化物）中的In、Cu、Cd、Sn、Fe、Zn等微量元素分析的基础上,结合不同类型矿床、不同矿物组合中硫化物的微量元素电子探针测试以及硫同位素分析结果,初步认为大厂锡矿岩浆源区是富铟的,在正常的沉积岩中不存在铟的初始富集;In主要赋存于闪锌矿中,与层状和块状的矿体关系密切。在成矿作用过程中,In的分布和富集对矿物组合和矿石类型具有明显的选择性。大厂铟矿的形成是富铟的岩浆源区重融产生含铟岩浆,在岩浆侵位冷却过程中,由岩浆结晶所产生的流体携带In、Cu、Fe、Zn、Sn等成矿元素从岩浆中出溶,形成含In的成矿流体。水-岩反应以及在大气降水来源流体的参与下,导致In、Cu、Fe、Zn、Sn等从成矿流体中沉淀、富集成矿。     

安徽峙门口铜-铁-金-硫矿床地球化学特征

峙门口铜—铁—金—硫矿床发育上部层状矿体和下部脉状矿体。上部层状矿石重晶石的δ~(34)S值为+14.10‰～+18.90‰。上部层状矿石黄铁矿和方铅矿的δ~(34)S值为+3.50‰～+5.84‰,下部脉状矿石黄铁矿的δ~(34)S值为+4.80‰～+6.80‰。下部脉状矿石中脉石英的δ~(18)O值为+14.3‰～+1 8.5‰,δ~(30)Si值为-0.3%0～-0.2‰。下部脉状矿石黄铁矿Re/Os比值为78.342～175.540,上(顶)部层状矿石中黄铁矿Re/Os比值为62.298～169.545。从下部脉状矿石到上部层状矿石,δ~(34)S值、Re/Os比值和流体包裹体温度249 ℃→97 ℃逐渐降低,~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb、~(208)Pb/~(204)Pb平均值和Os_总、Re、~(187)Re等含量逐渐增高。矿石黄铁矿Re-Os同位素等时线年龄303±33 Ma。地质地球化学特征反映峙门口铜—铁—金—硫矿床为海底热水喷流沉积成因。     

贵州纳雍水东铅锌矿床石英包裹体特征及成矿温度研究

利用显微测温学的方法,对纳雍水东铅锌矿床中石英进行显微及包裹体测温研究。研究表明,石英的流体包裹体主要以气液相包裹体居多,纯液相次之。包裹体测温结果显示,成矿流体冰点温度为-12.5℃~0.1℃,均一温度变化范围为122.1℃~307.0℃,峰值范围为120℃~150℃,反映出中低温成矿的特征;流体盐度W(NaC leq)%变化范围为0.18%~16.43%,平均盐度7.05%;流体密度为0.8 g/cm3~1.02g/cm3,平均密度0.95 g/cm3;成矿压力为87.86×105Pa~351.94×105Pa,其对应的成矿深度为0.29 km~1.17 km之间,平均成矿深度为0.50 km。综合研究表明本区矿床为典型的中低温热液铅锌矿床,成矿流体呈现中低温、低盐度、中等密度、低压、浅成相的矿床成矿环境特征。     

高放废物处置库甘肃北山预选区地下水位动态特征

阐明了甘肃北山预选区地下水位动态特征及其与当地大气降水的关系,并对其动态类型进行了剖析,由此得出北山地区地下水源自当地大气降水补给的认识。为处置库预选区场址评价提供了水文地质依据。     

湘赣桂地区加里东期构造变形特征及成因分析

系统解剖了华南早古生代地层出露较好且加里东运动比较典型的地区,包括广西的元宝山、越城岭、大明山、大瑶山、云开大山地区以及湘赣边境等地区。通过对其褶皱、断裂形态的描述与分析发现大明山、大瑶山地区EW向的寒武系褶皱是云开地块在晚寒武世-早奥陶世由南向北推覆挤压的结果,而桂北元宝山、越城岭地区及湘赣边境地区NE-NNE向的早古生代地层的褶皱是由于华夏地块与扬子地块在晚奥陶世-早志留世沿郴州-临武断裂收缩挤压的结果,而且这一收缩挤压是属于陆内造山事件而不是前人所说的洋陆俯冲事件和陆-陆碰撞造山事件,且加里东运动先由南向北、后由东向西逐渐拓展,变形强度由强到弱。     

江西城门山铜矿含矿斑岩体风化作用地球化学特征

文章利用城门山铜矿露天采坑系统地研究了含矿斑岩体风化作用过程中常量元素和微量元素的地球化学行为.结果表明,含矿斑岩体具有2个明显的风化旋回,风化作用过程主要表现为铝硅酸盐矿物的水解、水化作用,斑岩体中Ca、Mg、Na、K等元素大量淋失,Ca、Mg、Na淋失量可达80%以上,而Si、Al、Ti、Fe残留在风化层中.城门山铜矿含矿斑岩体具低Ti、Nb、Ta、Zr、Hf和低稀土元素含量(ΣREE=77.69×10-6～104×10-6),具有较稳定的Nb/Ta和Zr/Hf比值,稀土元素配分模式为较缓的右倾模式,无明显的铕异常(δEu＞0.73),ΣCe/ΣY比值为3～8.这些特征可作为评价城门山铜矿含矿中酸性岩体主要的地球化学指标之一.