鄂尔多斯盆地低渗透油气藏形成研究现状与展望

鄂尔多斯盆地是中国规模最大的低渗透油气资源勘探与开发基地,其低渗透油气藏具有油层物性差、非均质性强、油藏成藏因素复杂、油藏分布受多种因素联合控制等特点。在回顾鄂尔多斯盆地低渗透油气藏成藏理论研究和勘探历史经验基础上,认为目前鄂尔多斯盆地低渗透油气藏成藏研究存在两大理论体系,即沉积学控制成藏理论和运移动力学控制成藏理论,前者从沉积特征出发,强调储层砂体沉积相、非均质性和成岩作用在低渗透性油藏形成中的控制作用,后者从石油运移与聚集过程出发,强调运移动力学在初次运移和二次运移中的重要作用。但是目前低渗透油气成藏研究存在一定的局限性和片面性,过分强调了单个地质因素的作用,其中沉积学控制成藏理论局限于沉积相划分和沉积模式建立方面,过多地强调了沉积相对成藏因素静态的控制作用,而忽视了油气成藏过程的动态属性;运移动力学控制成藏理论却过分强调了油气流体运移过程的模式化和公式化,过分夸大和随意解释了油气运移成藏记录——油气包裹体的作用及其原始地质意义,轻视了深部地层条件下油气运移的复杂性和油气包裹体记录的多解性。因此,传统的单因素控制油气成藏理论和相应的勘探研究方法已经不能确切揭示油气富集规律和有效指导勘探工作。低渗透油气藏成藏理论研究趋势是要重视分析油气藏地质记录,动态研究油气藏形成和演化历史过程,总结油气富集规律,为油气勘探战略部署提供重要资料。     

Discriminating between pore‐filling load and bed‐structure load: a new porosity‐based method,exemplified for the river Rhine

Sediments contained in the river bed do not necessarily contribute to morphological change. The finest part of the sediment mixture often fills the pores between the larger grains and can be removed without causing a drop in bed level. The discrimination between pore‐filling load and bed‐structure load, therefore, is of practical importance for morphological predictions. In this study, a new method is proposed to estimate the cut‐off grain size that forms the boundary between pore‐filling load and bed‐structure load. The method evaluates the pore structure of the river bed geometrically. Only detailed grain‐size distributions of the river bed are required as input to the method. A preliminary validation shows that the calculated porosity and cut‐off size values agree well with experimental data. Application of the new cut‐off size method to the river Rhine demonstrates that the estimated cut‐off size decreases in a downstream direction from about 2 to 0·05 mm, covariant with the downstream fining of bed sediments. Grain size fractions that are pore‐filling load in the upstream part of the river thus gradually become bed‐structure load in the downstream part. The estimated (mass) percentage of pore‐filling load in the river bed ranges from 0% in areas with a unimodal river bed, to about 22% in reaches with a bimodal sand‐gravel bed. The estimated bed porosity varies between 0·15 and 0·35, which is considerably less than the often‐used standard value of 0·40. The predicted cut‐off size between pore‐filling load and bed‐structure load (D_c,p) is fundamentally different from the cut‐off size between wash‐load and bed‐material load (D_c,w), irrespective of the method used to determine D_c,p or D_c,w. D_c,w values are in the order of 10^?1 mm and mainly dependent on the flow characteristics, whereas D_c,p values are generally much larger (about 10⁰ mm in gravel‐bed rivers) and dependent on the bed composition. Knowledge of D_c,w is important for the prediction of the total sediment transport in a river (including suspended fines that do not interact with the bed), whereas knowledge of D_c,p helps to improve morphological predictions, especially if spatial variations in D_c,p are taken into account. An alternative to using a spatially variable value of D_c,p in morphological models is to use a spatially variable bed porosity, which can also be predicted with the new method. In addition to the morphological benefits, the new method also has sedimentological applications. The possibility to determine quickly whether a sediment mixture is clast‐supported or matrix‐supported may help to better understand downstream fining trends, sediment entrainment thresholds and variations in hydraulic conductivity.     

Zircon M257 ‐ a Homogeneous Natural Reference Material for the Ion Microprobe U‐Pb Analysis of Zircon

We introduce and propose zircon M257 as a future reference material for the determination of zircon U‐Pb ages by means of secondary ion mass spectrometry. This light brownish, flawless, cut gemstone specimen from Sri Lanka weighed 5.14 g (25.7 carats). Zircon M257 has TIMS‐determined, mean isotopic ratios (2s uncertainties) of 0.09100 ± 0.00003 for ²⁰⁶pb/²³⁸U and 0.7392 ± 0.0003 for ²⁰⁷pb/²³⁵U. Its ²⁰⁶pb/²³⁸U age is 561.3 ± 0.3 Ma (unweighted mean, uncertainty quoted at the 95% confidence level); the U‐Pb system is concordant within uncertainty of decay constants. Zircon M257 contains ～ 840 μg g^?1 U (Th/U ～ 0.27). The material exhibits remarkably low heterogeneity, with a virtual absence of any internal textures even in cathodoluminescence images. The uniform, moderate degree of radiation damage (estimated from the expansion of unit‐cell parameters, broadening of Raman spectral parameters and density) corresponds well, within the “Sri Lankan trends”, with actinide concentrations, U‐Pb age, and the calculated alpha fluence of 1.66 × 10¹⁸ g^?1. This, and a (U+Th)/He age of 419 ± 9 Ma (2s), enables us to exclude any unusual thermal history or heat treatment, which could potentially have affected the retention of radiogenic Pb. The oxygen isotope ratio of this zircon is 13.9%o VSMOW suggesting a metamorphic genesis in a marble or calc‐silicate skarn.     

软黏土蠕变特性试验研究：回顾与发展

大量的室内和现场试验表明软黏土存在长期变形难以收敛的问题,为了更深入地认识软黏土的蠕变特性,首先,从微观物理化学角度探讨蠕变机制;然后,深入分析一维应力条件下次固结系数的演变规律以及确定方法和三轴排水、不排水蠕变特性及黏土的长期抗剪强度、室内旁压试验和现场试验等复杂应力下的黏土蠕变特性等,并且讨论黏土蠕变特性与应变速率和应变松弛特性在一维和三轴条件下的关联性;最后,从黏土次固结特性与微观结构的相关性、如何准确描述次固结系数的非线性及蠕变过程中应力剪胀剪缩关系发展等三方面更深入地探讨软黏土蠕变特性。     

利用扫描电镜、压汞法、氮气吸附法评价近海黏土孔隙特征

近海地区黏土的微观结构单元--黏土畴中含有大量的粒内孔隙,其孔径小至纳米级,这部分孔隙对黏土的物理指标、水稳性、膨胀性、收缩性等具有重要影响,一般方法很难准确地描述其孔隙特征。试验利用扫描电镜、压汞法、氮气吸附法对湛江黏土的微观孔隙特征及其孔隙发育的控制因素分析,建立微观结构与物理指标、力学行为的相互关系与灵敏性分析。结果表明,湛江黏土具有不良物理性质和良好力学特性指标的异常组合,是一种高灵敏性的强胶结结构性黏性土,其机制主要是：湛江黏土的微观结构为带有胶质联结特性的、定向性无序的开放式絮凝结构,孔隙结构为具有较高的强度和空间稳定性的边－面－角联结的空间网架系统。由于特殊的孔隙网架结构以及“墨水瓶”型孔隙的存在,导致退汞过程出现滞留现象及产生吸附回线。研究表明,联合扫描电镜、压汞法、氮气吸附法能够准确、完整地对近海地区黏土孔隙体系特征进行定性与定量的评价。     

An analytical solution for the nonlinear distribution of effective and total stresses in vertical backfilled stopes

The increasing use of backfill in underground mines requires a proper evaluation of the stress state in and around the filled openings. This is, however, a relatively complex issue due, in part, to the large contrast in strength and stiffness between the backfill material and surrounding rock mass. In recent years, it has been shown that arching theory, based on limit equilibrium analysis, can be used to estimate the stress distribution in backfilled stopes. Nonetheless, many simplifications are involved in such analytical solutions and this affects the precision and significance of the calculated results. In this paper, a previously developed solution is enhanced by introducing the combined effects of non-uniform vertical stress distribution and positive pore water pressure. This leads to a more representative analytical solution, as demonstrated by successful comparisons with numerical simulations. The results indicate that the proposed solution can be used to estimate the effective and total stress state in submerged or partially submerged backfilled stopes with a simple geometry.     

Numerically observed shear bands in soft sensitive clays

The numerical challenges that arise in modelling shear bands in soft sensitive (SS) clays have not yet been fully resolved. Convincing and well-accepted solutions have yet to be found. This paper presents some novel information related to the shear band phenomenon in SS clays. In this study, the hypothesis is that the generation and dissipation of excess pore pressure from shear bands could regularise the strain softening and result in a mesh independent shear band thickness. The generation and dissipation of excess pressure is modelled by a coupled consolidation process. The simulation aims at modelling two counteracting mechanisms in the SS clay. First, the shear band narrows because of strain softening. Second, the internal pore water pressure drainage reduces the rate of strain softening. This counteracting mechanism provides an inherent regularisation technique for SS clays. This study presents some numerical results involving these two counteracting mechanisms. This study also shows that an inherent internal parameter applicable for SS clays can be defined by the ratio between soil permeability and the applied strain rate. In the case of SS clays, the range of this parameter varies from 0 to 0.0002 mm.     

Theoretical analyses of acidization dissolution front instability in fluid‐saturated carbonate rocks

This paper presents an instability theory that can be used to understand the fundamental behavior of an acidization dissolution front when it propagates in fluid‐saturated carbonate rocks. The proposed theory includes two fundamental concepts, namely the intrinsic time and length of an acidization dissolution system, and a theoretical criterion that involves the comparison of the Zhao number and its critical value of the acidization dissolution system. The intrinsic time is used to determine the time scale at which the acidization dissolution front is formed, while the intrinsic length is used to determine the length scale at which the instability of the acidization dissolution front can be initiated. Under the assumption that the acidization dissolution reaction is a fast process, the critical Zhao number, which is used to assess the instability likelihood of an acidization dissolution front propagating in fluid‐saturated carbonate rocks, has been derived in a strictly mathematical manner. Based on the proposed instability theory of a propagating acidization dissolution front, it has been theoretically recognized that: (i) the increase of the mineral dissolution ratio can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (ii) the increase of the final porosity of the carbonate rock can destabilize the acidization dissolution front, while the increase of the initial porosity can stabilize the acidization dissolution front in fluid‐saturated carbonate rocks; (iii) the increase of the mineral dissolution ratio can cause an increase in the dimensionless propagation speed of the acidization dissolution front; (iv) the increase of the initial porosity can enable the acidization dissolution front to propagate faster, while the increase of the final porosity can enable the acidization dissolution front to propagate slower in the acidization dissolution system. Copyright © 2012 John Wiley & Sons, Ltd.     

苏里格气田东部二叠系盒8段储层次生孔隙形成主控因素

苏里格气田东部下二叠统石盒子组8段是苏里格气田东部主要含气层位,其储集空间以各类次生孔隙为主。为明确次生孔隙控制因素,结合铸体薄片鉴定与定量统计、流体包裹体温度及成分分析等手段,对研究区盒8段储层次生孔隙特征及主控因素进行了系统研究。结果表明,苏里格气田东部盒8段储层次生孔隙的形成受有机酸溶蚀、深部热流体作用共同影响;平面分布受沉积相、构造及油气运移路径复合控制。沿构造鼻隆轴线方向、基底断裂结合部位与厚砂体叠合区附近次生孔隙最发育。     

不同温度、羧酸溶液中长石溶解模拟实验

报道了在100℃、140℃下微斜长石在不同羧酸溶液中的溶解实验数据。通过实验表明1)反应温度增高,可增强溶液中阳离子的活性和迁移性,加快长石溶解的反应速率,促进长石的溶解。2)在强酸性条件下,pH值的变化可影响长石的溶解。但在中等酸性条件下,pH值对长石的溶解影响很小。3)羧酸(乙二酸)可不同程度地促进长石溶解,可通过形成乙二酸络合物的形式,增加离子在溶液中的溶解度。但乙酸络合物的作用不明显。长石溶蚀导致岩石孔隙度变大,并且改善孔喉性质。同时,由于乙二酸络合物的存在,增加了Si在溶液中的溶解度,阻止了石英加大和其它成因SiO₂的生成,有利于次生孔隙和原生孔隙的保存。4)长石溶解使溶液中Al的浓度较高,但由于铝-羧酸络合物的亲油性比亲水性强,故有一部分Al被分配到油相中,这也是目前大多数油田水中Al浓度偏低的主要原因。