高阶动校正速度拾取方法在海域超压分布中的应用
Application of the velocity picking method based on high-order normal-moveout correction in predicting overpressure distributions in marine areas
第一作者:
收稿日期: 2025-02-21 修回日期: 2025-10-10
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Received: 2025-02-21 Revised: 2025-10-10
由于超压沉积盆地在海域中普遍存在且分布广泛,通常具备良好的油气成藏条件,对于油气资源评价与勘探部署具有重要的指导意义。速度是超压分布研究的关键参数,随着对预测超压分布精度要求的提高,对地震速度的精度和质量提出了越来越高的要求。海域井网较陆地钻井更为稀疏,因此地震速度的井约束不足,其可靠性需要多方评价,同时经常规速度分析或建模方法获取的地震速度容易存在分辨率不足的问题,因此采用基于非相关参数的高阶动校正为理论基础的高密度双谱速度拾取方法所获得的有利目标区更高分辨率的地震速度体是研究海域盆地超压分布的一种有效手段。本文首先介绍了高阶动校正的方法原理,随后展示了该方法在东海某探区的应用过程。实际应用表明:高阶动校正后的地震速度体可以更好地反映地下高压分布情况,表明该方法在海域超压分布研究中具有良好的应用前景。
关键词:
Overpressured sedimentary basins are ubiquitous and extensively distributed in marine areas.They typically possess favorable conditions for hydrocarbon accumulation,thus holding considerable significance for guiding hydrocarbon resource evaluation and exploration deployment.Velocity serves as a key parameter for research on overpressure distributions.The increasing demands for higher accuracy in overpressure distribution prediction impose higher requirements on the accuracy and quality of seismic velocities.Compared to well patterns in land areas,the more sparse well patterns in marine areas lead to insufficient well constraints on seismic velocities,requiring a comprehensive reliability evaluation.Additionally,seismic velocities obtained from conventional velocity analysis or modeling often show insufficient resolution.Therefore,this study proposed a high-density bispectral velocity picking method under the theoretical framework of high-order normal-moveout(NMO) based on uncorrelated parameters.The proposed method can obtain higher-resolution seismic velocity volumes for favorable target areas,providing an effective approach to exploring overpressure distributions in marine basins.This study first presented the theoretical principles of high-order NMO correction.Subsequently,it demonstrated the application of the proposed method in a specific exploration area in the East China Sea.The practical application suggests that seismic velocity volumes subjected to high-order NMO correction can effectively reflect subsurface overpressure distributions,showing promising prospects in the research on overpressure distributions in marine areas.
Keywords:
本文引用格式
刘苗, 邢雯淋, 杨雨松, 任静, 赵秀莲, 李振伟, 陈琳枝.
LIU Miao, XING Wen-Lin, YANG Yu-Song, REN Jing, ZHAO Xiu-Lian, LI Zhen-Wei, CHEN Lin-Zhi.
0 引言
由于地下超压分布一般在速度上呈现低速特征[12],因此地震速度体上的异常低速现象对超压分布范围具有一定的指示作用。随着压力预测精度要求的提高,地震速度的精度、分辨率及与测井速度的匹配度成为超压分析的关键制约因素。对于海洋勘探而言钻井成本相对较高,井网较陆地钻井更为稀疏,而地震速度的可靠性一般需要高质量的地震数据支撑和钻井约束,因此,在做压力预测时对于一般地震速度的可靠性需要进行多方面的评价分析。同时经常规速度分析或建模方法获取的地震速度的分辨率不足以准确反映目标地层速度的精细变化,难以判断是否存在异常压力地层等。
1 理论与方法
地层的各向异性广泛存在,由于垂向非均质性(射线弯曲或分层效应)和地下的各向异性介质所形成的反射动校时差曲线为非双曲线型,采用常规的动校正和速度分析方法不能将地震道集完全拉平,因此,在复杂介质中的动校正和速度分析必须考虑各向异性的问题[17]。
式中:t(VNMO)和t(VNMO,η)均表示总旅行时;η表示椭圆率参数(即时差非双曲程度的各向异性参数);VNMO为动校正速度;tp0表示纵波零偏移距的旅行时;x表示偏移距。从式(1)~(2)中可以推出,只需要椭圆率参数η和VNMO两个参数就可以处理一切时间域成像处理(如 NMO 校正、DMO 校正、叠前和叠后时间偏移等)。
基于波传播的相速度公式,Thomsen[20]提出了表征TI介质弹性性质的5个参数,分别为vp0、vs0、ε、γ和δ,对于VTI介质而言:
式中:vp0为准纵波速度(即沿TI介质垂直对称轴方向传播的相速度);参数ε表示垂直纵波速度和水平纵波速度差值与垂直纵波速度的比值,是度量纵波各向异性强度的参数;δ为纵波变异系数,表示垂向纵波各向异性变化的快慢程度。
在此基础上,Siliqi 等[14]针对各向异性主要集中出现在道集远偏移距范围的性质,对非双曲线时差方程(式(2))进一步修正得到:
式中:VNMO和η是两个非相关的关键参数,并且它们随偏移距对时差的影响是不规则分布的。其中VNMO参数对道集的全偏移距范围都有影响,而η只在远偏移距范围处有较大影响,当η=0时,式(5)又变为常规双曲线时差方程(式1),因此,必须将两个参数结合起来充分考虑才能更好地解决由于各向异性所导致的地震速度精度问题,即非相关参数的高阶动校正。
图1
图1
时差参数dtn和τ0之间的关系
Fig.1
Relation between time-difference parameters dtn and τ0
图2是高密度双谱速度分析,是基于V和η参数与τ0和dtn参数的非双曲线动校式(5)和式(6)形成的双谱面板左(dtn,τ0)和右(V,Van),其中dtn为剩余时差、τ0为零偏移距走时、V为NMO速度、Van为各向异性速度,面板上的颜色表示Semblance值(无量纲,范围 0~1),颜色越亮(红)表示相似性越高,参数组合更可靠。在拾取(dtn, τ0)面板中相应的dtn,τ0参数后再转换到(V,Van)面板中获取相应的V和η参数。从图2中可以看出左图中(dtn,τ0)面板高semblance区域(亮色)集中在一个狭窄范围内,比(V,Van)面板具有更好的约束性,表明dtn和τ0的解更稳定,τ0的变化被限制在表面最大值附近的一个小区域内(即颜色最亮区域对应的纵轴范围)。
图2
图2
双谱面板左图(dtn,τ0)和右图(V,Van)之间的差异
Fig.2
Difference between parameters (dtn,τ0) and (V,Van) in bispectral panels
为提升地震速度的分辨率来指示海域超压分布,采用基于非相关参数的高阶动校正理论的双谱速度拾取方法获取新的地震速度体,具体步骤如图3所示。
图3
图3
高阶动校正指示超压分布处理流程
Fig.3
Processing flowchart for non-hypobolic moveout correction in overpressure distribution indicatioon
1)数据准备:收集研究区的CRP地震道集和地震偏移速度体,首先对CRP地震道集进行优化处理,然后对道集进行反动校正处理;
2)高阶动校正:对反动校正后的道集采用高密度双谱自动速度拾取dtn和τ0参数,对拾取后的参数进行地质统计插值和滤波处理,然后属性转换为相应的V和η参数;
3)道集分析:将获取到的V和η数据应用到初始反动校正后的CRP地震道集,进行道集的二次动校正,通过道集的拉平效果判断新速度体的适用性;
4)分析结果质控:将高阶动校正后获得的新的地震速度体与已钻井速度进行对比分析,判断新速度体的可靠性;
5)压力应用:采用确定后的新速度体对超压分布有初步的指示作用,后续可以用于压力预测相关工作。
使用高阶动校正后获取的新的速度体相比于原始地震速度更能反映出地层内局部细小的速度差异,相应的更能反映地下的实际情况,对超压在地下的分布范围具有一定的指示作用,同时也为后续的压力预测工作提供了更高精度的地震速度体。
2 应用效果
为了验证采用上述流程获得的新速度体对超压分布的指示作用,本文选取了东海某工区的相关数据进行应用。该区域的前期钻探已获得较好的油气突破,目前通过钻井已确认井中存在异常高压区域(图4),压力系数达到1.49(压力系数>1为超压),由于地层压力与声波时差(可转换为声波速度)呈现负相关关系,因此,在出现异常高压区域范围应出现异常低速现象[12]。将声波测井速度曲线以井柱的形式投影到地震速度体上可以看出(图4),井速度曲线的速度变化与地震偏移速度基本一致,但在异常高压位置(虚线红框)井速度呈现明显的低速特征(色彩柱红黄色区域为低速区域),而速度体在异常高压位置(虚线红框)虽存在低速特征,但其大小和范围并不明显。
图4
图4
原始偏移速度体与井速度和高压分布的关系
Fig.4
Diagram of relationship between the initial migration velocity data and high pressure distribution through well
图5
图5
高阶动校正后速度体与井速度和高压分布的关系
Fig.5
Diagram of relationship between the velocity data after non-hypobolic moveout correction and high pressure distribution through well
为了验证高阶动校正得到的地震速度体的准确性,采用新的地震速度对原始反动校正后的CRP地震道集进行动校正拉平。图6是经过高阶动校正处理前后的道集对比,可以看出双参数高阶算法处理后的道集在大偏移距可以得到进一步的拉平,提高CRP地震道集质量,初步证明了高阶动校正得到的地震速度体的准确性。之后将声波测井速度、原始地震偏移速度以及高阶动校正后的新速度进行对比分析,如图7与井速度对比。可以看出高阶动校正后的新速度与声波测井速度更加匹配;从图7b所示的与井速度误差对比可以看出,高阶动校正后的新速度与测井声波速度的误差整体上低于原始地震偏移速度与测井声波速度的误差,因此,可以证明高阶动校正后的新速度是准确的,并且相比原始地震偏移速度具有更高的精度。
图6
图6
道集高阶动校正前后对比
Fig.6
Comparison of seismic gather before and after applying non-hypobolic moveout correction
图7
图7
高阶动校正后速度与原始地震偏移速度和测井速度对比
Fig.7
Comparison between original seismic migration velocity,corrected seismic velocity and acoustic logging velocity after non-hypobolic moveout correction
3 结论
基于Siliqi等[14-
但值得注意的是该方法对原始地震数据质量具有依赖性,原始CRP道集的信噪比直接影响参数拾取精度,未消除的噪声可能导致各向异性假象或异常速度值,因此该方法在应用前需确保道集经过充分的噪声压制和振幅补偿处理,并进行参数敏感性分析(如V±5%、η±5%的扰动测试)评估参数稳定性。最终成果应综合测井曲线分析等进行多维度验证,以规避单一方法的不确定性风险。
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