台湾海峡盆地九龙江凹陷火成岩发育特征及其油气地质意义

基于二维地震剖面的精细地质解释,并结合磁力和钻井资料分析,开展了九龙江凹陷火成岩发育特征、岩浆活动和区域构造与盆地演化关系及其油气地质意义的研究。分析认为,九龙江凹陷经历了始新世中晚期、中新世中晚期二期火山活动,火成岩在地震剖面上主要表现为板状、锥状及块状三种地震相类型,钻井主要揭示了喷发、侵入及火山碎屑三大类型火成岩,它们的发育与分布是区域性构造事件和盆地演化相作用的结果。始新世中晚期火山活动产生的高温有利于烃源岩在短期内经历高温的催化改造而生成油气,形成的火成岩体岩墙面可以增加和改善凹陷中央区油气向西部斜坡的运移,该火成岩附近区的一些圈闭在成岩期受热液蚀变的影响,储层孔、渗性得到改善的同时也会致使储层发生不同程度的变质,在今后的勘探开发中是一个值得关注的问题。     

海洋磁力梯度测量技术在水合物勘探中的应用

在天然气水合物勘探中,海底的泥底辟和泥火山构造是重要的研究对象。在高分辨率地震剖面解释中,直接识别泥底辟构造存在一定困难,主要因为泥底辟构造和火成岩侵入体在形态上十分相似,容易造成解释的多解性。本文就目前天然气水合物调查中存在的这些特殊技术问题。通过对海上高精度磁力测量技术方法研究、广州海洋地质调查局“海洋四号”船在南海北部东沙海域的海上试验、对试验结果的系统研究分析以及磁测和地震剖面两种手段的综合解释,成功地尝试了用高精度海洋磁测成果中的磁力总场和梯度变化特征来识别水合物勘探中高分辨率地震剖面上的泥底辟构造真伪的技术方法。     

利用重磁震资料解释推断东海海底火成岩

利用1∶100万上海幅海洋区域地质调查项目最新获得的重力、磁力和多道地震数据,根据研究区内重、磁场特征,以及已知的火成岩发育状况,在数据处理的基础上,通过剖面和平面相结合,对东海海底的火成岩进行了推断解释,从而得到火成岩在空间上的展布位置。分析认为东海海底火成岩具有沿北北东向成带发育的特点,沿深大断裂侵入于中生代地层;北北西向火成岩带发育时间较晚,规模小,与北西向断裂形成较晚相对应,火成岩分布呈现东西分带的特点,陆架盆地中低部隆起为喜马拉雅早—中期岩浆岩。     

海洋磁力梯度测量技术在水合物勘探中的应用

在天然气水合物勘探中,海底的泥底辟和泥火山构造是重要的研究对象。在高分辨率地震剖面解释中,直接识别泥底辟构造存在一定困难,主要表现为泥底辟构造和火成岩侵入体在形态上十分相似,容易造成解释的多解性。本文就目前天然气水合物调查中存在的这些特殊技术问题,通过对海上高精度磁力测量技术方法研究,在南海北部东沙海域的海上试验,试验结果的系统研究分析以及磁测和地震剖面两种手段的综合解释,成功地尝试了用高精度海洋磁测成果中的磁力总场和梯度变化特征来识别水合物勘探中高分辨率地震剖面上的泥底辟构造真伪的技术方法。     

南堡凹陷馆陶组火山事件及其油气地质意义

南堡凹陷新近系馆陶组地层沉积时期凹陷内火山活动剧烈.通过测井分析及地震解释表明,火山喷发物的岩性以玄武岩为主,形成于新近系早期.平面分布上具有东北薄、西南厚,纵向上具有多期叠置发育的特点.综合分析认为,大量的火山物质改变了凹陷的地貌形态,影响了后继河流相沉积地层的空间分布,在西部地区形成大量的地层圈闭.由于火山事件的热...     

台湾海峡西部地震地层分析

利用在台湾海峡西部采集的近万公里地震反射资料及围区地质、钻井及地震资料,对晋江凹陷和九龙江凹陷地震反射剖面进行了较详细的描述与分析,以及地震层序和地震相划分,对各地震层序及地震相分别进行了地质年代与沉积相探讨,并首次把九龙江凹陷T_3~0—T_g超层序解释为中生代地层的不同见解,这对研究该区海域沉积史、生油气史、油气储层和盖层,以及进一步开展油气勘探有十分重要的意义。     

地震调查在南黄海崂山隆起的发现及其石油地质意义

崂山隆起位于南黄海中部,是南黄海中、新生代盆地的隆起构造单元,其调查与研究程度极低,新近系之下是否有沉积地层一直没有得到资料的证实。近年来战略性油气地质调查工作在该区新近系之下发现了层状地层,根据地震反射特征分析、重磁震联合反演和区域地质对比,推测为海相古生界,是下扬子区古生界的海上延伸。这一发现对推动南黄海海域油气新领域、新层位的调查与勘探具有重要的石油地质意义。     

渤海湾盆地埕北凹陷古近系沉积特征与油气圈闭

为了研究渤海湾盆地埕北凹陷的勘探前景和油气成藏规律,基于埕北凹陷古近系隐蔽油气藏的勘探实践,探讨了埕北凹陷的沉积特点、沉积体系以及油气圈闭特征。对勘探地质资料的研究表明:埕北凹陷古近系主要沉积了沙河街组和东营组,其中沙河街组以沙三段为主,东营组地层较全;埕北凹陷古近系沉积具有多旋回性,具有多期次的沉积间断,凹陷南北沉积差异较大;埕北凹陷古近系主要发育了近岸水下扇、扇三角洲—滑塌浊积扇、远岸浊积扇、辫状河三角洲、低弯度河—泛滥平原、湖底扇等沉积体系,并对应形成了各类油气圈闭。这些圈闭都是油气成藏的有利储集体。以上结论表明,埕北凹陷古近系沉积特征有利于油气成藏。     

东海陆架区中北部前第三系基底综合地球物理研究

从地震、钻井资料出发,结合周边地质特征,推断东海陆架区中北部存在中生界和古生界地层。结合地震资料,正演消除了海底和新生界密度不均匀在重力场上的影响,定量反演重、磁力异常并求取了重力基底和磁性基底。重力基底的特征在东西分带的大背景下表现出“靠陆侧南北分块,靠洋侧东西分带”的特点。西湖凹陷区的磁性基底与重力基底埋深大致相同,不一致地方可能是受岩体的影响。西湖凹陷以西地区,包括海礁凸起等单元,总体出现磁性基底埋深比重力基底埋深深2km左右,初步解释为古生界地层的反映。中生界地层厚度的分布也具有东西分带和南北分块特点。西湖凹陷西缘的中生界地层厚度大,其中带中生界虽然含有一定的火山岩或火山碎屑岩,但沉积岩更多,这对下一步的油气勘探有利。     

匹配追踪谱反演处理技术在精细地震解释中的应用

受地震资料分辨能力的限制,薄储层、微小断层等小尺度地质体刻画始终是困扰油田精细勘探与开发的难题之一。基于匹配追踪算法的频谱分解反演技术为提高地震综合解释精度提供了一条新的途径。该技术在高精度频谱分解基础上不依赖于先验模型及解释层位等约束,基于叠后地震数据体可直接反演并得到地震反射系数序列。该数据体具备很高的分辨能力,作为基础数据在地层层序细节刻画、薄储层及小断层等微小地质目标识别等方面具有明显优势。该技术在渤海数个油田中进行应用并取得较好效果,具有广阔的应用前景。     

Comparison of high-resolution seismic profiles and the geoacoustic properties of Eckernförde Bay sediments

High-resolution seismic profiles of Eckernförde Bay and the adjacent Baltic Sea were collected, and the geoacoustic properties of sediments there were measured. Bulk densities averaged ~ 1.35 g cm^–3 and ranged from ~ 1.2 to ~ 1.7 g cm^–3. Compressional wave velocities in gas-free sediments averaged ~ 1460 m s^–1 and ranged from ~ 1425 to ~ 1555 m s^–1. In nongassy sediments, bulk density variations typically controlled changes of acoustic impedance. Impedance changes were usually too small and closely spaced to be resolved seismically, although, at certain sites, significant impedance changes are far apart enough that they correlate one-to-one with seismic reflectors. Where free gas is present, velocity decreases and wave energy is scattered, causing a prominent seismic reflector.     

Crustal structure and deformation associated with seamount subduction at the north Manila Trench represented by analog and gravity modeling

We investigated the deformation in the accretionary wedge associated with subducted seamounts in the northern Manila Trench by combining observations from seismic profiles and results from laboratory sandbox experiments. From three seismic reflection profiles oriented approximately perpendicular to the trench, we observed apparent variations in structural deformation along the trench. A number of back-thrust faults were formed in the accretionary wedge where subducted seamounts were identified. In contrast, observable back-thrusts were quite rare along the profile without seamounts, indicating that seamount subduction played an important role in deformation of the accretionary wedge. We then conducted laboratory sandbox experiments to investigate the effects of subducted seamounts on the structural deformation of the accretionary wedge. From the analog modeling results we found that seamount subduction could cause well-developed back-thrusts, gravitational collapse, and micro-fractures in the wedge. We also found that a seamount may induce normal faults in the wedge and that normal faults may be eroded by subsequent seamount subduction. In addition, we constrained the crustal structure of the South China Sea plate from modeling free-air gravity data. The dip angle of the subducting plate, which was constrained by hypocenters of available earthquakes, increased from south to north in the northern Manila Trench. We found a laterally heterogeneous density distribution of the oceanic crust according to the gravity data. The density of subducted crust is ~2.92 g/cm³, larger than that of the South China Sea crust (2.88 g/cm³).     

Comparison of sedimentation-compression curves obtained by nuclear and gravimetric methods for Wilkinson Basin,Gulf of Maine,sediments

Accurate measurements of bulk density are important in the construction of sedimentation-compression curves of water-saturated, fine-grained cohesive sediments for consolidation studies. The bulk density of five cores was measured nondestructively on a laboratory nuclear transmission densitometer and the water content, expressed as void ratio, was derived from an empirical relationship between bulk density and water content. Bulk density and water content measured destructively was determined every 10 cm for a comparison with the nuclear data. Agreement between nuclear and gravimetric methods was within ± 0.02 g/cm³ for bulk density ranging from 1.2 to 1.4 g/cm³. Sedimentation-compression curves made using both methods were in generally good agreement.In the Wilkinson Basin, void ratio gradually decreases with increasing effective overburden pressure. This indicates that consolidation by dewatering the surficial sediments is normal and that the environmental conditions during deposition remained relatively constant.     

Estimating saturation of gas hydrates using conventional 3D seismic data,Gulf of Mexico Joint Industry Project Leg II

We present a methodology for generating pre-drill estimations of hydrate saturations using conventional 3D seismic data. These seismic-based estimates will be compared with well log derived saturations from the subsequently drilled wells of the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II (JIP Leg II) expedition.Predicting saturation of gas hydrates (S_h-seismic) combines pre-stack seismic inversion, rock physics modeling and stratigraphic interpretation. Before the wells were drilled, no nearby sonic and density logs were available to define and calibrate the elastic property trends for the shallow target interval containing the gas hydrate stability zone. Therefore, rock property trends were established by applying principles of rock physics and shallow sediment compaction, constrained by known regional geological parameters. S_h-seismic volumes were generated by inverting pre-stack data to acoustic impedance (PI) and shear impedance (SI) volumes, and then analyzing deviations from modeled impedance trends. To enhance the quality of the inversion, the signal-to-noise ratio of the offset data was maximized by conditioning the seismic prior to inversion. Seismic stratigraphic interpretation plays an important role by identifying the more promising strata and structures for the presence of gas hydrates.The pre-drill S_h-seismic results are compared with saturations calculated from log data, S_h-log, of the wells drilled in the JIP Leg II campaign. Due to weaker seismic reflections, predictions may be less accurate for low concentrations, such as saturations less than 40%, and for thin intervals below the vertical resolution of the seismic data (about 15 m). However, the integrated geophysical workflow is very effective for identifying and quantifying significant hydrate concentrations, making the method a promising prospecting technique.     

珠母贝人工繁育优化技术的研究

在室内水泥池分别进行了移池培育、不同种类附着器、光照强度、水流和冲洗对珠母贝附着幼虫变态和稚贝存活的研究,结果表明:附着密度为2.18个/cm~2±0.50个/cm~2时,移池培育,其变态幼虫密度为0.95个/cm~2±0.13个/cm~2,20 d稚贝存活密度0.41个/~2±0.08个/cm~2,移池培育显著提高附着幼虫变态和稚贝存活;附着板、附着绳、网片、小石块变态幼虫密度分别为0.70个/cm~2±0.08个/cm~2、1.38个/cm~2±0.15个/cm~2、0.97个/cm~2±0.12个/cm~2、1.04个/cm~2±0.28个/cm~2,稚贝存活密度分别为0.36个/cm~2±0.06个/cm~2、0.62个/cm~2±0.07个/cm~2、0.45个/cm~2±0.07个/cm~2、0.60个/cm~2±0.08个/cm~2,附着绳显著提高附着幼虫变态和稚贝存活;光照强度为300～600 lx时变态幼虫密度为0.87个/cm~2±0.07个/cm~2,20 d稚贝存活密度0.45个/cm~2±0.08个/cm~2,强光不利于幼虫的变态和稚贝存活;水流速为2.3 cm/s时变态幼虫密度为1.08个/cm~2±0.07个/cm~2,20 d稚贝存活密度0.87个/cm~2±0.07个/cm~2,冲洗的变态幼虫密度为1.64个/cm~2±0.19个/cm~2,20 d稚贝存活密度1.00个/cm~2±0.12个/cm~2,水流或冲洗显著提高附着幼虫变态和稚贝存活.     

Lithospheric structure below the eastern Arabian Sea and adjoining West Coast of India based on integrated analysis of gravity and seismic data

Four uniformly spaced regional gravity traverses and the available seismic data across the western continental margin of India, starting from the western Indian shield extending into the deep oceanic areas of the eastern Arabian Sea, have been utilized to delineate the lithospheric structure. The seismically constrained gravity models along these four traverses suggest that the crustal structure below the northern part of the margin within the Deccan Volcanic Province (DVP) is significantly different from the margin outside the DVP. The lithosphere thickness, in general, varies from 110–120 km in the central and southern part of the margin to as much as 85–90 km below the Deccan Plateau and Cambay rift basin in the north. The Eastern basin is characterised by thinned rift stage continental crust which extends as far as Laxmi basin in the north and the Laccadive ridge in the south. At the ocean–continent transition (OCT), crustal density differences between the Laxmi ridge and the Laxmi basin are not sufficient to distinguish continental as against an oceanic crust through gravity modeling. However, 5-6 km thick oceanic crust below the Laxmi basin is a consistent gravity option. Significantly, the models indicate the presence of a high density layer of 3.0 g/cm³ in the lower crust in almost whole of the northern part of the region between the Laxmi ridge and the pericontinental northwest shield region in the DVP, and also below Laccadive ridge in the southern part. The Laxmi ridge is underlain by continental crust upto a depth of 11 km and a thick high density material (3.0 g/cm³) between 11–26 km. The Pratap ridge is indicated as a shallow basement high in the upper part of the crust formed during rifting. The 15 –17 km thick oceanic crust below Laccadive ridge is seen further thickened by high density underplated material down to Moho depths of 24–25 km which indicate formation of the ridge along Reunion hotspot trace.     

Mechanical properties of calcareous silts in a hydraulic fill island-reef

Abstract

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33?g/cm³, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33?g/cm³, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.     

Study of the sedimentation and self-weight consolidation behavior of seafloor sediments using a radioisotope densitometer

ABSTRACT

In this study, settling tests were conducted to investigate the sedimentation and self-weight consolidation behavior of seafloor sediments from Isahaya Bay, Ariake Sea, Japan. During the tests, the density variations with depth and time were measured by a gamma-ray transmission radioisotope densitometer. The test results show that the settling process of the seafloor sediments can be classified into the flocculation stage, settling stage, and consolidation stage. The settling rate of the seafloor sediments in the settling stage is dependent on the temperature and initial water content, while the settling rate in the consolidation stage is independent of the temperature and initial water content. The density profile changes from a constant density profile to a linear density profile when the sedimentation process transitions to the self-weight consolidation process. The relations between the void ratio (e) and effective vertical stress (p’) at very low pressures can be calculated from the measured density values, and this can be used for the analysis of the self-weight consolidation of seafloor sediments. For the seafloor sediments tested in this study, the undrained shear strength (s_u) values are almost the same when the density values are less than 1.14?g/cm³, and the s_u values increase linearly with an increase in density when the density values are in the range of 1.14–1.2?g/cm^3.     

南极布兰斯菲尔德海峡及邻区地壳结构反演及构造解析

南极布兰斯菲尔德海峡及邻区是南极半岛海域火山、地震等新构造运动最活跃的地区,由于前人对资料处理解释的差异,导致盆地的构造格局仍部分存疑。本文以研究区的卫星重力数据为基础,以多道反射地震和部分岩性资料为约束,采用重震联合反演方法构建了三条横跨研究区的地壳结构剖面,并进一步研究布兰斯菲尔德海峡盆地的地壳结构。研究结果表明布兰斯菲尔德海峡盆地莫霍面深度为33—38km。菲尼克斯板块俯冲消减下沉至南设得兰岛弧之下,导致南设得兰海沟的俯冲带后撤,产生3—4km厚的岩浆混染地壳,密度为2.9g/cm~3。分析认为受板块运动和弧后扩张影响,沿布兰斯菲尔德海峡盆地扩张脊分布的海底火山裂隙式喷发,并进一步导致盆地的持续性扩张。     

A seismic study to investigate the prospect of gas hydrate in Mahanadi deep water basin,northeastern continental margin of India

The presence of gas hydrates, one of the new alternative energy resources for the future, along the Indian continental margins has been inferred mainly from bottom simulating reflectors (BSR) and the gas stability zone thickness mapping. Gas hydrate reserves in Krishna Godawari Basin have been established with the help of gas-hydrate related proxies inferred from multidisciplinary investigations. In the present study, an analysis of 3D seismic data of nearly 3,420 km² area of Mahanadi deep water basin was performed in search of seismic proxies related with the existence of natural gas hydrate in the region. Analysis depicts the presence of BSR-like features over a large areal extent of nearly 250 km² in the central western part of the basin, which exhibit all characteristics of a classical BSR associated with gas hydrate accumulation in a region. The observed BSR is present in a specific area restricted to a structural low at the Neogene level. The coherency inversion of pre-stack time migration (PSTM) gathers shows definite inversion of interval velocity across the BSR interface which indicates hydrate bearing sediments overlying the free gas bearing sediments. The amplitude versus offset analysis of PSTM gathers shows increase of amplitude with offset, a common trend as observed in BSR associated with gas hydrate accumulation. Results suggest the possibility of gas hydrate accumulation in the central part of the basin specifically in the area of structural low at the Neogene level. These results would serve as preliminary information for selecting prospective gas hydrate accumulation areas for further integrated or individual study from geophysical, geological, geochemical and microbiological perspectives for confirmation of gas hydrate reserves in the area. Further, on the basis of these results it is envisaged that biogenic gas might have been generated in the region which under suitable temperature and pressure conditions might have been transformed into the gas hydrates, and therefore, an integrated study comprising geophysical, geological, geochemical and microbiological data is suggested to establish the gas hydrate reserves in Mahanadi deep water basin.