辽西葫芦岛东部表层调查方法比对实验

地震勘探中,近地表的不均匀性给激发、接收和静校正等工作带来较大困难。辽西葫芦岛东部地表地质条件复杂,浅表层速度及厚度差异大,表层调查工作直接影响到地下介质成像效果。为使该地区首次进行的地震勘探能够获取准确的静校正量数据、给井深设计提供依据、研究适合该区域的表层调查方法,同时为满足国家深部探测项目对实验方法比对研究的需求,结合小折射、地面微测井和井中微测井三种表层调查方法的工作原理,在该工区分别应用三种方法做同点比对实验,分析了不同调查方法的适用性及精确度。结果表明,三种方法得到的结果与岩性录井结果一致,均能有效探测高速层埋深,指导井深设计,其中:小折射成本较低,适合地面较平坦区段,虽然不够精细,但能够准确找到高速层,可用于井深设计或作为微测井方法的补充;地面微测井适合山高无水或者造山破碎带造成钻井严重漏水的地区,需要井中检波器与大地良好耦合;井中微测井最为精确,探测层位更为精细,能分辨更多层位,与岩性录井结果最接近,在静校正量获取方面具有明显优势。通过三种表层调查的比对,分析了不同方法的适用范围,为该工区选择合适的表层调查方法及方法参数选取提供依据,同时为其他地表复杂区域进行表层调查提供参考。     

微测井资料三维表层速度统计建模方法研究

在西部复杂山地地震勘探中,静校正问题尚未完全得到解决,其主要原因是表层速度模型存在困难。微测井测量作为一种传统的较准确的表层速度调查手段,不受复杂地表条件限制,适用于复杂地区观测,但其生产成本高,不能保证逐点连续观测,因而不能直接获得连续的近地表速度模型。这里研究出了起伏地表微测井离散数据地质统计三维建模方法。首先建立基于起伏地表和微测井速度分层的地质框架模型,由地震勘探测量数据形成地表面,依据地质统计技术生成与地形相关的低速带、降速带底面,在此基础上形成微测井离散数据表层速度模型。将该方法应用于川东北HCL工区,利用三百七十口微测井离散数据得到了三维表层速度模型,与微测井速度对比,模型速度精度较高。     

瞬变电磁法在准噶尔盆地南缘东部台28井区近地表调查中的应用

瞬变电磁法(TEM)是近年来国内外发展速度较快、应用效果较好的一种电磁方法,由于其施工便利、成本低廉、工作效率高、应用效果明显等优点,已广泛应用于金属、煤炭、地下水等矿藏勘查.该方法应用于地震勘探中的表层结构调查,虽不能直接得到近地表地质体岩性信息.但可通过连续观测获取不同岩性间电性差异信息,根据电性相对关系得到准确的近地表地质体形态和岩性分布规律,为地震资料后续处理提供可靠的静校正量.瞬变电磁法勘探深度由浅层5 m到中深层300 m左右.准噶尔盆地南缘东部台28井区勘探实例表明,通过电性分层、小折射和地震微测井成果资料综合解释,在表层结构建模和计算静校正量方面取得良好效果.     

多道面波分析技术在沙漠低降速带调查中的应用

结合鄂尔多斯盆地北部塔巴庙地区低、降速带的调查实例,简述多道面波分析MASW在沙漠地区的应用,并将反演结果与小折射资料进行对比说明其运用效果.实践表明,在采集和处理参数选取合理的情况下,最大勘探测度可以达60 m,完全可以满足实际工作需要.在近地表构造复杂地区采用多道面波分析技术进行低、降速带情况调查,可以弥补小折射和微测井调查的不足,展现出受地表环境影响较小的优越性.     

三湖地区真假含气异常识别和消除技术及应用

中国西部的柴达木盆地三湖地区是中国陆上中大型气田,天然气储量丰富,勘探潜力巨大。勘探实践证实,该区存在表层低速带引起的地震剖面异常和地层含气引起的地震异常,并都以"低频、强振幅、同相轴下拉"的特征展现在地震剖面上。该区地表相对比较平坦,以往表层调查工作比较少,难以识别和消除表层低速带引起的地震异常,严重影响该区天然勘探开发进程。这里首先采用共偏移距技术和双域反射时间特征技术较好识别表层结构异常带,其次采用精细表层调查和初至反演表层结构建模来确定表层结构异常带,最后采用高精度模型约束初至折射静校正技术较好消除该区表层低速带引起的地震异常。通过实际资料验证,该方法取得良好应用效果,较好解决该区由于巨厚低降速带引起的地震剖面异常的识别和消除问题,也为类似地区的地震勘探,提供了一个参考。     

库车复杂地表区伪三维表层建模与静校正技术

塔里木盆地库车山地一直是塔里木油田油气勘探的重点区域之一,但是该区地表条件复杂多样,表层调查、建模困难,静校正问题突出。这里通过采用微测井约束的浅层层析表层调查方法、伪三维表层建模及综合静校正技术,准确剖析了该区的表层结构,提高了剖面的成像效果,为类似区域的表层建模及静校正工作提供了借鉴。     

准噶尔南缘山前齐古背斜综合约束近地表速度建模

齐古背斜位于北天山山前南缘第一排构造带上,油气富集。工区内河流冲积扇体发育,沟壑纵横,表层速度结构复杂,难以准确建立近地表速度模型,影响地震成像。通过微测井约束的层析反演方法建立近地表速度模型,据表层结构调查、齐古背斜地质图、卫星照片对模型进行对比分析,同时结合层析反演严格的质控手段,对模型进行综合约束,经多次迭代得到合理的近地表速度模型,以此为基础计算静校正量并应用于地震数据处理中,通过叠加剖面检查进一步验证近地表模型的准确性。     

FOCUS折射静校正技术在准噶尔盆地腹部沙漠地区中的应用

准噶尔盆地腹部沙漠地区低降速带厚度和地表沙丘起伏较大,静校正问题突出.FOCUS折射静校正技术结合微测井解释成果能较好地解决陆西高分辨率攻关二维LH200602的静校正问题,相比准噶尔盆地地震勘探中通常使用的绿山折射静校正软件,FOCUS折射静校正技术无需进行数据格式转换和重新定义观测系统,工作效率高,为该区解决静校正问题提供了另一种可行方法.     

时变校正方法研究与应用

地表一致性静校正方法的基本假设是:地震波在低降速带为垂直入射、垂直反射,即地表同一位置,静校正量只与低降速带的厚度、速度和充填速度有关,而与地震波的传播路径无关.这一假设是为了计算表层的延迟时而对表层模型的近似.随着地震勘探的不断精细,以往的构造勘探逐步转向岩性勘探,叠加剖面地震响应的地质特征是正确岩性反演结果的基础.因此叠加过程中如何减小对振幅、频率、波形的影响,处理中如何保护好岩性信息是实现勘探转型的关键.本文通过模型道的约束,利用相关方法,消除了地表非一致性引起的剩余时差,使反射相位同相性增强,减少了叠加过程对地震高频成份的损失及对地震波形的改变,有利于地震属性的反演和AVO油气检测的自动识别.     

折射延迟时与时深曲线反演模型法静校正技术

地震波在沙丘中的传播速度与沙丘厚度密切相关.利用延迟时反演高速顶界时,采用常速或插值方法求取表层速度,不能正确反应这种变化关系,使反演模型底界存在误差,影响静校正精度.利用微测井成果数据拟和得到时深曲线,再利用延迟时从时深曲线求取表层速度和厚度可有效解决此问题.方法为:解释和分析地震微测井数据→应用地震微测井或有代表性表层结构线段拟合时深曲线→利用野外单炮初至时间获取表层延迟时→应用延迟时与时深曲线反演近地表结构模型→静校正量计算.应用结果表明,该方法快速有效,在M10JQ3D中获得较好效果.     

基于震源垂向组合的浅层低速带多次反射折射波压制方法

低速带发育地区地震记录中的多次反射折射波严重影响波场中相近的反射波，导致反射波形态畸变，影响了对地震资料的正确解释。在阐明浅层低速带多次反射折射波产生机理和传播规律的基础上，提出垂向组合双震源的压制方法。根据勘探前期小折射、微测井等方法获取浅层参数信息，结合多次反射折射波与有效波之间相对位置关系，给出需要对多次反射折射波进行压制的前提条件，然后根据震源组合公式计算得到垂向组合参数可选范围，用于调整低速带中垂向设置的两个震源的相对位置，在不影响目的层反射波的基础上压制多次反射折射波。在正演模拟和黄土塬勘探区试验中，对比了常规单炮记录与震源垂向组合记录。结果表明:震源垂向组合方法在一定程度上能较好地压制浅层低速带多次反射折射波，有效提高地震数据信噪比和解释精度。      

层析法在黄土塬区近地表结构调查中的应用

我国西部黄土塬区的静校正问题十分突出,精细、准确的近地表结构调查对于解决激发井深的设计和静校正问题尤为重要,但该区的常规小折射解释精度极低,微测井难以追踪到高速层。在充分试验的基础上,提出了一种新的近地表结构调查方法——层析近地表结构调查法,该方法有效解决了上述难点,与常规小折射方法比较,该方法获取的近地表结构信息更丰富,刻画的近地表结构更为精细,能够较好地用于井深设计和静校正处理中初始模型的建立。     

工程地震折射波解释方法研究进展

地震折射波勘探是工程与环境地球物理中应用最为广泛的方法之一。作为一种简洁方便又经济实惠的勘探方法,它可为工程地质提供近地表地层起伏变化和速度横向变化以及潜水面变化资料等。随着工程地质勘查和城市地质勘探工作的发展,工程地震折射波法数据处理与解释变得尤为重要。本文主要介绍了浅层地震折射波法的发展历程、应用条件,并总结和讨论了几种主要折射波解释方法的原理。在此基础上,比较并讨论了各种方法在应用中的优势和不足,阐述了近年来国内外浅层地震折射波法的发展现状及趋势,并着重介绍了作为研究热点的折射层析成像方法。研究表明：当探测深度较浅且分界面足够平整、界面倾角较小时,最方便的解释方法是截距时间法;当勘探目标的深度达到25 m时,t₀差数法最为适用;勘探目标埋深超过25 m时,应当使用广义互换法。随着勘探精度要求越来越高,使用折射波走时层析成像技术可以满足纵横向速度变化的近地表地层,包括大倾角地层、隐伏层、界面起伏层等。     

Efficiency of seismic attributes in detecting near-surface cavities

The purpose of this study is to evaluate the efficacy of using seismic attributes to detect near-surface cavities. The methods used in this study include interpreting dispersion curves and amplitude mapping of the multichannel analysis of surface wave (MASW) technique and interpreting the delay in first arrivals of compressional waves. To test these methods, a seismic survey was conducted above a known near-surface cavity in Al-Suman Area, Saudi Arabia. The cause of the cavity is carbonization in the area; there are many cavities similar to this one. The seismic data were collected using a seismograph system with 48 vertical geophones. Both techniques show a tangible result for detecting the cavity. The 2D section of shear wave velocity, which was obtained by inverting the dispersion curves from the MASW technique, leads us to determine the shape of the cavity, as described by a low-velocity zone. Frequency against relative offset is plotted and shows a significant frequency drop in the presence of the cavity, which also provides an indication to the presence of cavity underneath. This interpretation is matched by the interpretation of observed delays in first arrivals of compressional waves. The integration of both P wave seismic refraction and MASW gives confidence in the result and matches observations of the existing cavity closely.     

Seismic vulnerability assessment in the new urban area of Diriyah Governorate,Riyadh, Saudi Arabia

Nine seismic refraction profiles were conducted and processed to study the near-surface sediments in the new urban area of Diriyah. The 2D geoseismic models illustrate two layers: a surface layer of soft sediments and weathered to hard limestone bedrock. Moreover, microtremor measurements were performed at 38 sites for 40 min using three-component seismographs and processed to assess the peak spectral amplitude and the corresponding fundamental resonance frequency. The seismic vulnerability index at each measurement site was estimated. These results correlate well with the geotechnical borehole data. The north-western zone is highly vulnerable due to the great thickness of the soft sediments.     

Multichannel analysis of surface waves (MASW) for seismic site characterization using 2D genetic algorithm at Bahrah area,Wadi Fatima,Saudi Arabia

The present study deals with the seismic site classification of Bahrah area, Wadi Fatima, to characterize the local site conditions. The dynamic behavior of sediments was studied by the application of surface wave inversion. The multichannel analysis of surface waves (MASW) shallow geophysical technique was utilized for site classification. MASW survey was carried out at 66 sites along with 13 seismic refraction profiles at suitable localities. MASW and seismic refraction profiles were processed and compared with the available borehole data. The integration of MASW techniques with seismic refraction and borehole data progressively enhanced the subsurface visualization and reliability of the shear wave velocity estimation in the subsurface in the study area. The subsurface shear-wave velocity model was achieved by the solution of an inverse problem-based dispersion of surface waves and propagation in a vertically heterogeneous medium. The 2D genetic algorithm was employed for the inversion of dispersion curves to obtain velocity and thickness of subsurface layers. The depth to engineering bedrock and velocity of shear waves in the first 30 m was deciphered and mapped. The depth of bedrock in study area varies from 4 to 30 m, and V _{S 30} ranges from 320 to 800 m/s. The most of study area falls in B and C class categories in addition to few sites of D class according to the NEHRP guidelines.     

Near-surface seismic refraction applied to exploring subsurface clay layer at a new mining area in southeast Cairo, Egypt

A near-surface seismic refraction survey was conducted at a new mining area located in southeast Cairo, Egypt, to explore the subsurface clay layer for future economic use in mining and cement industry. The purpose of the survey has been to provide geological and geophysical information because no borehole was existent in the area under investigation. The aim of study had been to explain the main characteristics of the subsurface layers. For this purpose, a new technique has been used to acquire and process the data. This technique provides critical information to determine the depth of the subsurface layers, as well as morphology, stratigraphy, and potential locations of the clay layer for future economic use. The thickness and general shape of the clay layer in the whole area were determined and are illustrated in maps.     

厚黄土覆盖地区有利激发层位选取方法

合理选取激发层位可有效提高巨厚黄土覆盖地区原始地震数据信噪比及分辨率,而单一的浅层折射、瞬态面波、微测井等手段常因复杂的浅表层地质条件,难以分出黄土层中的高速小层或薄层。利用微测井约束的瑞雷波反演方法,可以准确的划分浅表层速度界面的深度,进而确定激发层位的位置。以山西万荣、洪洞二项目为例,介绍了该方法的地质效果：其中万荣勘探区解释速度界面深度分别为27m、37m与45m,确定激发层位为37m深的高速粘土层,地震资料解释成果经3口钻孔验证,钻遇煤层最大相对误差约3%;洪洞勘探区以2、3层的粘土（15~18m）作为激发层位,其资料解释成果经1口钻孔验证,钻遇煤层相对误差约5%。     

2-D velocity structure in Kerala-Konkan basin using traveltime inversion of seismic data

The existence of gas-hydrates in marine sediments increases the seismic velocity, whereas even a small amount of underlying free-gas reduces the velocity considerably. The change in velocities against the background (without gas-hydrates and free-gas) velocity can be used for identification and assessment of gas-hydrates. Traveltime inversion of identifiable reflections from large offset multi channel seismic (MCS) experiment is an effective method to derive the 2-D velocity structure in an area. We apply this method along a seismic line in the Kerala-Konkan (KK) offshore basin for delineating the gas-hydrates and free-gas bearing sediments across a bottom simulating reflector (BSR). The result reveals a four layer 2-D shallow velocity model with the topmost sedimentary layer having velocity of 1,680–1,740 m/s and thickness of 140–190 m. The velocity of the second layer of uniform thickness (110 m) varies from 1,890 to 1,950 m/s. The third layer, exhibiting higher velocity of 2,100–2,180 m/s, is interpreted as the gas-hydrates bearing sediment, the thickness of which is estimated as 100 to 150 m. The underlying sedimentary layer shows a reduction in seismic velocity between 1,620 to 1,720 m/s. This low-velocity layer with 160–200 m thickness may be due to the presence of free-gas below the gas-hydrates layer.