Grain‐size variability within a mega‐scale point‐bar system,False River,Louisiana

Point bars formed by meandering river systems are an important class of sedimentary deposit and are of significant economic interest as hydrocarbon reservoirs. Standard point‐bar models of how the internal sedimentology varies are based on the structure of small‐scale systems with little information about the largest complexes and how these might differ. Here a very large point bar (>25·0 m thick and 7·5 × 13·0 km across) on the Mississippi River (USA) was examined. The lithology and grain‐size characteristics at different parts of the point bar were determined by using a combination of coring and electrical conductivity logging. The data confirm that there is a general fining up‐section along most parts of the point bar, with a well‐defined transition from massive medium‐grained sands below about 9 to 11 m depth up into interbedded silts and fine–medium sand sediment (inclined heterolithic strata). There is also a poorly defined increase in sorting quality at the transition level. Massive medium sands are especially common in the region of the channel bend apex and regions upstream of that point. Downstream of the meander apex, there is much less evidence for fining up‐section. Finer sediment accumulated more readily after the establishment of a compound bar in the later stages of construction, at the terminal apex and in the bar tail. This work implies that the best reservoir sands are likely to be located in the centre of the point bar, deposited in a simple bar system. Reservoir quality decreases towards the bar edge. The early‐stage channel plug is largely composed of coarsening‐upward cycles of silt to clay and is dominated by clay and clayey silt material with poor reservoir characteristics.     

Anomalous electrical resistivity anisotropy in clean reservoir sandstones

We report novel laboratory measurements of the full electrical resistivity tensor in reservoir analogue quartzose sandstones with clay contents less than 1.5%. We show that clean, homogeneous, visually uniform sandstone samples typically display between 15% and 25% resistivity anisotropy with minimum resistivity normal to the bedding plane. Thin‐section petrography, analysis of fabric anisotropy, and comparison to finite‐element simulations of grain pack compaction show that the observed anisotropy symmetries and magnitudes can be explained by syn‐depositional and post‐depositional compaction processes. Our findings suggest that: electrical resistivity anisotropy is likely to be present in most clastic rocks as a consequence of ballistic deposition and compaction; compaction may be deduced from measurements of electrical anisotropy; and the anisotropy observed at larger scales in well logging and controlled‐source electromagnetic data, with maximum resistivity normal to bedding, is most likely the result of meso‐scale (10^?1 m–10¹ m) periodic layering of electrically dissimilar lithologies.     

电阻率成像的混合正则化反演算法

利用混合正则化方法对二维分片常值电阻率进行反演研究,该方法结合了全变差正则化方法(total variation regularization)和经典吉洪诺夫正则化方法(classical Tikhonov regularization)的优点. 全变差正则化能够有效地重构分片常值电阻率和识别边界,而经典吉洪诺夫正则化方法则能有效地重构光滑的电阻率,从数值算例中可以看出,将这两种方法有效地结合到一起能够改进重构效果.     

青藏高原东北缘合作-大井剖面地壳电性结构研究

青藏高原东北缘合作-大井剖面的大地电磁探测结果表明,该区域的电性结构呈明显的纵向分层、横向分块的特点,中下地壳普遍存在高导层.青藏高原东北缘西秦岭北缘断裂带、北祁连南缘断裂带、北祁连北缘断裂带(海原断裂带)及龙首山南缘断裂带等区域性断裂带在电性结构模型中均表现为电性梯度带或低阻异常带.电性结构的横向分区与构造上的地块划分有明显的一致性,各个地块的电性结构存在明显差异.西秦岭北缘断裂带作是一个大型的板块边界,但板块结合带附近没有明显逆冲或俯冲痕迹,可能主要以左旋走滑为主.北祁连地块向北仰冲与阿拉善地块向南俯冲边界可能不是海原断裂带,而是龙首山南缘断裂带.西秦岭造山带内的壳内高导层与青藏高原内部存在的高导层具有可对比性,可能是由于部分熔融与含盐水流体共同作用的结果.中祁连地块内的高导层可能是含盐水流体引起的.而北祁连与河西走廊过渡带内的高导层则可能是板块俯冲或仰冲的构造运动痕迹,也可能是由含盐水流体引起的.     

自适应hp-FEM在随钻电阻率测井仪器响应数值模拟中的应用

随钻电阻率测井仪器响应数值模拟在电法测井仪器研制和资料处理与解释中具有重要的意义.本文利用自适应hp有限元算法(hp-FEM)模拟和分析了地层各向异性以及相对倾斜对仪器接收信号幅值比和相位差的影响,并对仪器响应特性进行了评价;同时,利用HERMES有限元软件包与VC++开发平台相结合,可以对随钻电阻率测井仪器响应数值模...     

随钻电磁波传播方位电阻率仪地质导向关键技术

随钻电磁波传播方位电阻率仪器在钻井过程中可以提供地层边界的方位及距离信息,因此在地质导向应用中发挥着重要作用,是提高油气资源开采率的重要手段.该技术是国外近十年来发展起来的前沿技术,在国内尚属空白.本文首次构思并实现了一种应用"交联天线"的随钻电磁波传播方位电阻率仪器,并从天线结构,测量原理,数据处理以及地层电阻率成像及解释等几个方面详细阐述.交联天线由极化方向正交的线圈串绕组成,同时具有方位探测和地层背景电阻率测量的功能.通过分析交联天线的电压在仪器旋转过程中的变化规律,可以计算出仪器所在地层的电阻率,判断地层边界的方位以及估算地层边界相距仪器的距离.该随钻电磁波传播方位电阻率仪器还包括用于常规电磁波传播电阻率测试的多频多测距补偿天线结构.结合地层电阻率测量及其在方位上的相对变化,可以实现对地层电阻率的全方位成像.该仪器在国内油田进行了多次实井测试,测试结果证明仪器能够在水平井地质导向中准确提供仪器所在地层的电阻率,以及地层边界方位和距离信息.已有实井测试结果表明仪器在油层(100Ωm)和泥岩(5Ωm)中的地层边界探测深度分别为2.2m和1.6m,平均误差在0.2m以内.     

基于非结构网格的电阻率三维带地形反演

地表起伏地形在野外矿产资源勘察中不可避免,其对直流电阻率法勘探影响巨大.近年来,电阻率三维正演取得诸多进展,特别是应用非结构网格我们能够进行任意复杂地形和几何模型的电阻率三维数值模拟,但面向实际应用的起伏地形下电阻率三维反演依然困难.本文基于非结构化四面体网格,并考虑到应用GPS/GNSS时,区域地球物理调查中可非规则布设测网的实际特点,实现了任意地形(平坦或起伏)条件下、任意布设的偶极-偶极视电阻率数据的不完全Gauss-Newton三维反演.合成数据的反演结果表明了方法的有效性,可应用于复杂野外环境下的三维电法勘探.     

南北地震带南段川滇黔接壤区电性结构特征和孕震环境

本文利用大地电磁测深数据,对穿过兰坪—思茅地块和川滇菱形地块以及进入扬子地块的云南兰坪—贵州贵阳大地电磁测深剖面展开了深部电性结构研究.采用大地电磁数据处理分析以及反演技术,对观测资料进行了由定性到定量全面地分析,通过二维非线性共轭梯度反演得到了沿剖面的较为详细的地壳上地幔电性结构,结合其他地质和地球物理资料的分析,对该剖面的二维电性结构进行解释,确定了主要断裂带和边界带的位置以及深部延伸情况,同时确定了壳内低阻层的分布位置,最后进行了区域动力学和孕震构造环境的探讨.研究表明:剖面壳幔电性结构分块性特征与区域地质构造分布特征基本一致,不同地块的电性结构存在显著差异,其中川滇菱形地块的结构相对复杂,上地壳的电性结构为高低阻相间分布特征,电阻率的突变带与地表断裂具有很好的对应关系;兰坪—思茅地块存在中上地壳低阻层,川滇菱形地块中西部存在下地壳低阻层,川滇菱形地块东部和华南地块西部存在中上地壳的低阻层;川滇菱形地块中部攀枝花附近的低阻层埋深最深,而华南地块西部会泽附近的低阻层埋深则最浅;兰坪—思茅地块和川滇菱形地块的中下地壳的低阻层可能与青藏高原物质的东南逃逸有关;华南块体的宣威以东的下地壳不存在低阻层,华南块体下地壳和上地幔的电阻率较高;攀枝花附近的高阻体可能是峨眉山玄武岩喷发导致底侵作用及幔源物质上侵的结果.     

海拉尔盆地中-上地壳电性结构特征研究

本文通过对横穿海拉尔盆地的一条长约222km的北西—南东向大地电磁测深剖面数据的定性分析及二维定量反演解释,首次获得了海拉尔盆地高精度大范围的电性结构图.海拉尔盆地中-上地壳电性结构纵向上具有典型的分层特性,总体可分为四层,即低阻层-高阻层-低阻层-高阻层,而横向上又具有分块特点.海拉尔盆地边缘及内部分布的众多断裂将盆地划分为隆起与坳陷相间的格局,并发现盆地内部坳陷区也存在有小规模凸起,每一构造单元内部电性结构各具特点.海拉尔盆地中-上地壳低阻层底面最深达28km,通常在6~16km之间,但厚度变化不大,在4~10km之间,且隆起区与坳陷区底面埋深差别较大.据电性结构模型推测出两条新断裂F8和F9,且断裂F9规模较大,为基底断裂.中-上地壳的低阻层可能在一定程度上控制着海拉尔盆地内油气田的分布格局.     

Controlled‐source electromagnetic monitoring of reservoir oil saturation using a novel borehole‐to‐surface configuration

To advance and optimize secondary and tertiary oil recovery techniques, it is essential to know the areal propagation and distribution of the injected fluids in the subsurface. We investigate the applicability of controlled‐source electromagnetic methods to monitor fluid movements in a German oilfield (Bockstedt, onshore Northwest Germany) as injected brines (highly saline formation water) have much lower electrical resistivity than the oil within the reservoir. The main focus of this study is on controlled‐source electromagnetic simulations to test the sensitivity of various source–receiver configurations. The background model for the simulations is based on two‐dimensional inversion of magnetotelluric data gathered across the oil field and calibrated with resistivity logs. Three‐dimensional modelling results suggest that controlled‐source electromagnetic methods are sensitive to resistivity changes at reservoir depths, but the effect is difficult to resolve with surface measurements only. Resolution increases significantly if sensors or transmitters can be placed in observation wells closer to the reservoir. In particular, observation of the vertical electric field component in shallow boreholes and/or use of source configurations consisting of combinations of vertical and horizontal dipoles are promising. Preliminary results from a borehole‐to‐surface controlled‐source electromagnetic field survey carried out in spring 2014 are in good agreement with the modelling studies.