复杂断裂带高精度地震采集技术及效果

[收稿日期]2011203216　[作者简介]孙永强(19642),男,2005年大学毕业,工程师,现主要从事地震采集生产技术管理工作。

复杂断裂带高精度地震采集技术及效果 孙永强,晁如佑,宗晶晶李亚斌,李金莲,付英露　(江苏石油勘探局地球物理勘探处,江苏扬州225007)[摘要]“十一五”期间,江苏油田相继在GY 凹陷的HL 、ZW 和WB 断裂带部署了YA 、ZD 、Z L 和CB共4块高精度三维地震采集区域。

3个断裂带断层发育,构造破碎,火成岩对下伏地层能量屏蔽严重,地震资料品质较差;地表条件复杂,激发、接收条件横向变化大。

为此,从观测系统、激发和接收3方面入手开展方法研究,形成了面向目标的观测系统优化技术、以精细表层结构调查为重点的最佳激发参数优选技术、基于保护高频成分的接收等技术,寻找到了一套适合GY 凹陷复杂断裂带的高精度地震采集技术系列,达到了落实小断层分布,提高地震资料品质的目的。

[关键词]复杂断裂带;GY 凹陷;高精度;地震采集方法[中图分类号]P631144[文献标识码]A [文章编号]100029752(2011)0720088204为进一步提高GY 凹陷HL 、ZW 和WB 断裂带的资料品质,江苏油田于“十一五”期间相继部署了YA 、ZD 、ZL 和CB 共4块高精度三维地震采集区域,通过地震采集方法研究和实践应用,最终获得了较高品质的原始地震资料,取得了很好的勘探效果。

1　采集难点1)三个断裂带构造破碎,波场复杂,不利于构造的准确成像[1,2]。

2)火成岩分布广泛,屏蔽作用强,影响了下伏地层的成像质量[3]。

3)原有地震资料信噪比低,反射能量弱,断裂带内层位难以追踪,小断层欠落实,影响构造的可靠程度。

4)工区表层结构多变。

分为胶泥、流沙和软泥等激发接收区[4];激发岩性变化较快;古河道发育[5],常引起局部地区单炮品质变差。

2　关键采集技术211　面向目标的观测系统优化技术观测系统设计原则是每个CDP 面元内炮检距和方位角分布均匀;保证目的层有效反射信息有利于速度分析和成像;确保目标区的有效覆盖次数,使地震资料有足够的信噪比;覆盖次数均匀,有利于构造和岩性研究[6～11]。

在全面分析GY 凹陷复杂断裂带高精度地震采集难点的基础上,提出应用基于射线理论和波动方程的地震波数值模拟技术,采集参数论证过程中,针对构造破碎、火成岩屏蔽提出基于叠前成像的三维观测系统设计概念,根据高精度采集及满足勘探开发不同阶段的需求,采用可变面元技术,并应用照明技术优化采集观测系统的设计。

面元的尺寸有4种,分别为10m ×10m 、10m ×20m 、20m ×20m 、20m ×40m 。

以YA 高精度三维地震资料为基础,通过采集方法后评估,优化采集方案。

以20m ×20m 面元为・88・石油天然气学报(江汉石油学院学报)　2011年7月　第33卷　第7期Journal of Oil and G as T echnology (J 1J PI )　J ul 12011　Vol 133　No 17 图1　20m ×20m 面元信噪比与覆盖次数关系估算图例,根据信噪比计算公式[12]:S/N =20lg (P s /P n )(其中,P s 为信号的能量值;P n 为噪声的能量值),得到信噪比与覆盖次数关系估算图(图1)。

由图1可见,覆盖次数小于120次,信噪比较低;大于240次,信噪比改善不明显;覆盖次数在120次与240次之间,信噪比提高最大。

针对火成岩屏蔽,增加炮检距排列长度,从图2可以看出,远道叠加有利于减弱火成岩的影响。

结合参数论证,最大炮检距选择3690m 。

最终采用24线20炮正交观测系统10m ×10m 面元52次覆盖次数进行精细地震资料采集,20m ×40m 面元覆盖次数达到416次,大大提高了剖面的信噪比,资料上的断层显示较以往更清晰。

图2　火成岩对不同炮检距叠加的影响模拟图212　激发参数优选技术针对GY 凹陷表层结构复杂的特点,利用小折射、微测井等资料进行表层结构建模。

在表层结构复杂的地区和局部表层速度倒转的区域增加微测井密度。

通过做折射微测井,结合岩心、钻井以及微测井解释成果建立岩性2速度模型,以建立岩性与表层速度的准确关系,形成了高精度表层结构调查技术。

在精细的表层结构调查基础上落实激发围岩的岩性特征,选择不同岩性区域进行激发井深和药量试验,在全工区进行逐点的激发井深设计,确保激发能量,保障采集质量。

一般在流沙区选择15m 井深激发,在胶泥区选择12m 井深激发。

在软泥较厚的地区加大井深,在速度反转的区域,打穿低速层激发,选择激发频率和能量耦合比较好的围岩激发。

在胶泥中激发的地震子波一致性好、能量强。

药量的大小与能量成正比,药量过大干扰也增强,药量过小反射能量小。

试验后确定的最佳药量为6～8kg 。

213　接收参数优选技术大面积组合检波压制高频信息、使频带变窄的缺点已成为地震采集工作的瓶颈。

高精度地震采集应采用小面积组合,全噪声信号,为室内压噪提供完整的波场信息。

结合表层调查结果,对检波器组合进行分析,选取动态范围大、小组合基距检波器面积组合,有效・98・第33卷第7期孙永强等:复杂断裂带高精度地震采集技术及效果　压制噪声并保护高频信号[13]。

采用2串24个检波器,设计出6种组合方案,对6种检波器组合方式绘制频率特性曲线图,并进行量化分析,如表1所示,可以得出检波器“回”字形(F 组合)方式的有效波频带都位于通放带内;在压制带内,该组合方式有利于压制噪声,从试验结果也证明该种组合所获得的资料品质较高,能够提高主频,频带较宽。

最终采用24个检波器“回”字形组合,组内距2m 、组合基距8m ,有利于保护高频信号。

表1　各种检波器组合方式的量化分析参数表组合方式组合基距L x /m 组合基距L y /m Inline 方向通放带压制带Crossline 方向通放带压制带矩形组合(A )1080～100Hz 有利于压制噪声0～120Hz 有利于压制噪声长方形组合(B )1440～70Hz 有利于压制噪声0～160Hz 压制噪声效果差长方形组合(C )740～120Hz 有利于压制噪声0～160Hz 压制噪声效果差点放(D )00完全通放完全通放线性组合(E )011完全通放0～80Hz 有利于压制噪声“回”字型组合(F )880～100Hz 有利于压制噪声0～100Hz 有利于压制噪声3　采集效果分析1)监视记录　从监视记录分析结果看,原始单炮记录面貌总体较好,记录能量较强,浅、中、深层反射波组齐全,同相轴清楚连续。

整体来看,胶泥区激发单炮记录品质最好,流沙区单炮记录品质稍次之。

如图3所示,与以往的三维单炮记录相比,高精度三维采集的原始单炮记录资料频带较宽、主频较高。

图3　高精度三维原始单炮记录(左)与以往三维单炮记录(右)对比2)处理剖面　高精度地震资料信噪比高、波组特征明显。

火成岩之下地层信息更丰富,T 33波组反射的改善,为落实阜宁组圈闭提供了资料基础;目的层段主频有明显提高,频带宽、分辨率较高;主控断层及断阶带内面貌明显改善,小断层的断点更加清晰,更容易识别,能更精细刻画小断块。

如图4所示,该次高精度采集的剖面比以往相同部位的老资料品质有明显提高。

3)勘探成果　高精度三维资料更精确地反映真实地层产状,成图的深度误差更小;资料品质的改善带来构造格局的再认识。

HL 、ZW 两大断裂带勘探效果显著,探井成功率达6617%,新增探明储量608×104t 。

特别是Y38井戴南组隐蔽油气藏的成功发现,拓展了油田的勘探领域。

・09・　石油天然气学报(江汉石油学院学报)2011年7月图4　高精度三维处理剖面(左)与以往剖面(右)对比4　结 论1)高精度三维地震勘探技术对复杂断裂带起着非常重要的作用,由于采样密度大、精度高,反射面元属性更加均匀合理,非常有利于提高地震资料处理中的复杂断层和复杂小断块成像精度,小断层得到精细刻画、落实。

2)高精度三维地震勘探能很好地提高地震资料品质,断阶带内资料信噪比较老资料有了明显的提高,在此基础上提交的钻探井位有了较好的发现。

3)高精度采集成为江苏油田目前能够提供满足勘探开发需求地震资料的重要技术方法。

在今后的勘探进程中,高精度三维地震采集技术将发挥重要的作用,特别是对于复杂断裂带、复杂小断块的勘探意义深远,必将带动该领域的勘探新发现,具有广阔的应用前景。

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