叠前油气检测技术在渤海Y构造浅层的应用
中海石油(中国)有限公司天津分公司 渤海石油研究院,天津 300450
The application of pre-stack hydrocarbon detection to Y structure of Bohai Bay Basin
Bohai Oilfield Research Institute,Tianjin Branch of CNOOC Ltd.,Tianjin 300450,China
责任编辑: 叶佩
收稿日期: 2019-08-14 修回日期: 2020-07-15 网络出版日期: 2020-10-20
基金资助: |
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Received: 2019-08-14 Revised: 2020-07-15 Online: 2020-10-20
作者简介 About authors
张京思(1986-),女,硕士,工程师,主要从事地球物理解释与储层研究工作。
渤海Y构造浅层明化镇组储层发育,但已钻井证实该区储层含油气性有较大差异。高精度的地震流体检测结果对提高目标区明下段岩性圈闭钻探成功率意义重大。为研究目标区明下段储层含油气性,对目的层进行了一系列基于振幅类和频率类的叠后含油气性检测,但都无法对储层流体进行有效识别,可靠性较低。因此,转变研究思路,应用叠前流体检测技术,通过方法对比发现,在入射角小于30°时,直接通过叠前角道集提取出的流体因子对该区浅层油气较为敏感,与已钻井测井解释结果对应较好。应用该敏感参数进行储层含油气性预测取得了较好的效果。对类似地区叠前储层流体预测具有一定的借鉴意义。
关键词:
The Minghuazhen Formation of the Y structure in Bohai Bay Basin is well developed,but the drilled wells confirm that the oil-bearing characteristics of reservoirs have big differences in this area.The high reliability of reservoir fluid detection results are of great significance in improving the success rate of lithologic traps in the lower Minghuazhen Formation of the structure and activating the whole structure.In order to study the oil-gas bearing feature of the target area,the authors used a series of post-stack oil-gas detection methods based on amplitude and frequency,but still failed to identify the reservoir fluid effectively and reliably.By changing the research idea and using pre-stack hydrocarbon detection technology and method comparison,it is found that,when the incident angle is less than 30 degrees,the fluid factor directly extracted from pre-stack angle gathers is more sensitive to shallow oil and gas in this area,which corresponds well to the well logging interpretation results.The application of this sensitive parameter to the prediction of reservoir oil-gas bearing feature has achieved good results.It has certain reference significance for pre-stack reservoir fluid prediction in similar areas.
Keywords:
本文引用格式
张京思, 边立恩, 王军, 刘腾, 于娅.
ZHANG Jing-Si, BIAN Li-En, WANG Jun, LIU Teng, YU Ya.
0 引言
在石油勘探中,利用流体因子进行储层含油气性识别是目前常用的烃类检测方法。Smith和Gidlow[1]率先提出流体因子的概念,并利用流体因子来预测岩性和流体。Hilterman等[2]对Shuey近似方程进行了分析,提出了利用泊松比反射率作为油气指示因子。随后,Fatti[3]重新组合了Aki-Richards近似方程,利用加权叠加的方法提取出纵横波反射率,并对Smith和Gidlow流体因子进行改进,提高了流体识别的可靠性。Goodway等[4]根据Fatti等的研究成果,提出使用拉梅常数和剪切模量与密度乘积作为流体指示因子的LMR法,其研究成果具有重大意义。Batzle等[5]提出了将体积模量与剪切模量的差作为流体识别因子的k-μ法。Russell等[6]对前人研究成果进行了总结,基于Gassmann理论将Gassmann流体项与密度乘积作为新的流体指示因子。上述流体因子岩石物理意义明确且对孔隙流体较敏感,具有较好的普适性,在现阶段储层流体识别中占据主要地位。张会星等[7]通过求解波动方程,推导出双相介质中地震波衰减系数计算公式,提出利用地震资料的低、高频段信息反演地下介质含油气性的方法。印兴耀等[8]提出了双相介质理论指导下的流体因子精细构建与应用,其构建的拟流体模量参数相较于其他常规流体参数,对储层流体具有更强的敏感性。目前,随着技术的进步及学者们认识的不断加深[9],利用多种弹性参数,通过分析流体因子的重构机理、物理意义,新的更为敏感的流体因子被构建,从而更加有效地对储层含油气性进行识别[10]。
近年来,渤海新近系勘探由构造逐渐向岩性转变,油气成藏情况愈加复杂,高精度的储层流体识别对提高勘探成功率至关重要。本次研究应用油藏放大镜软件,以高质量的叠前道集资料为基础,以固流解耦思想为指导,以Russell近似公式为理论依据,提取敏感流体因子,应用于渤海Y构造浅层明化镇组储层流体预测中,取得了较好的应用效果。
1 叠前流体检测原理
在Gassmann等人的研究基础上,Russell进一步对多孔流体饱和岩石的弹性参数及AVO理论进行了研究,其中多孔流体饱和岩石的纵波速度vp与横波速度vs分别表示为:
式中:β=1-
Russell通过研究孔隙介质的AVO理论,提出了Russell近似公式[15]:
式中:f,μ和ρ分别为界面两侧介质的流体因子、剪切模量、密度;Δf,Δμ和Δρ分别为界面两侧介质的流体项、剪切模量、密度的差值;θ为平均入射角度,
叠前道集的优化处理是进行AVO异常识别及叠前反演的前提,高质量的叠前道集资料能够提高储层及储层含油气性预测的精度。以高精度储层流体预测为目的,建立了系统的叠前储层流体预测流程。首先对叠前CRP道集资料品质进行分析,包括频谱分析、振幅分析、入射角分析等,并研究单井附近道集AVO特征是否与实际正演AVO特征相匹配,如果叠前CRP道集质量较好,可直接转为角道集进行储层流体预测。但一般常规处理得到的叠前道集资料很难满足AVO分析及叠前弹性参数反演、流体预测的要求[17],需对叠前道集进行以保真、保幅为核心的道集优化处理,最终使单井道集AVO特征与正演AVO特征相匹配,然后提取流体项进行储层流体检测。
2 实际应用
渤海Y构造位于石臼坨凸起南部斜坡带上,它是在一定基底隆起背景影响下,受石南二号断裂控制形成的一系列浅层断鼻、断块构造。该构造在明化镇组时期为曲流河沉积,已钻井揭示,其砂泥比在20%~30%之间,储盖组合较好,曲流河砂体发育,物性较好。从已钻的7口井来看,明化镇组储层含油气性具有较大的差异性,而高精度的流体识别是该区研究的难点。
为研究目标区储层的含油气性,并为井位部署提供依据,前期进行了基于振幅类和频率类的叠后油气检测[18],效果均不理想。因此本文转变研究思路,在前人认识的基础上进行叠前油气检测。首先针对叠前CRP道集存在的问题进行一系列道集优化处理,然后在高质量的叠前角道集资料的基础上对目标储层进行固流解耦AVO属性的流体检测,取得了满意的效果,最终优选出两个有利勘探目标。油气检测结果为井位部署提供了参考,尽最大可能规避了钻井风险,在勘探阶段具有重要意义。
2.1 叠前道集优化处理
通过对叠前CRP道集进行分析认为,研究区目的层叠前道集资料远道信噪比较低,存在多次波,频率变低,并且存在剩余时差,单井附近道集质量较差,AVO分析的散点较散,相关系数较低(图1),难以满足叠前储层预测及流体检测的需要。针对叠前道集存在的问题,利用奇异值分解技术对叠前道集进行去噪处理,并进行远道切除,保留所需范围之内的有效信号;用射线路径追踪计算非零炮检距地震道与零炮检距地震道的吸收差异,进行与炮检距有关的横向振幅吸收补偿;并采用反射轴自动追踪的方法,自动拾取相对时间偏移量,将道集数据拉平。最终使叠前CRP道集资料信噪比提高,剩余时差消除,单井道集AVO特征与正演AVO特征一致(图2、图3),为后续储层流体预测奠定了基础。
图1
图2
图2
原始道集(a)与处理后道集(b)对比
Fig.2
The contrast of original gathers(a) and processed gathers(b)
图3
图3
油层顶(a)与水层顶(b)AVO特征对比
Fig.3
AVO characteristics comparison between oil top(a) and water top(b)
2.2 油气检测
首先对Y构造浅层明化镇组实际测井资料进行分析,通过计算得到相应的流体项Δf/f(表1)。
表1 含油砂岩与含水砂岩流体因子值
Table 1
砂岩类型 | Δf/f平均值 |
---|---|
含油砂岩 | -7.25 |
含水砂岩 | -14.5 |
通过表1可以发现,流体项Δf/f对识别储层流体比较敏感,当储层含油时,Δf/f绝对值偏小,当含水时Δf/f绝对值增大。因此可以通过计算流体项Δf/f来对Y构造明化镇组储层流体进行识别。
前人的研究中,一般通过波阻抗反演来提取流体因子,而本研究则以高质量的叠前角道集数据为基础,以Russell近似公式为理论依据,通过已钻井得到的目的层段纵横波速度数据拟合出公式vp=1.24×vs+1230作为运算参数,并输入外部均方根速度体,计算流体项Δf/f,对研究区目的层储层进行含油气性预测。
渤海Y构造共钻探7口井,每口井的含油气性具有一定差异,其中Y-3井钻遇的单层油层最厚,因此在烃检结果剖面上有较好的响应特征(图4),剖面中颜色表示流体值的大小,井上绿色标注代表钻遇油层,蓝色标注代表钻遇水层。Y-4井没有钻遇油层,因此在烃检结果剖面上,目的层段无响应特征。其余5口井均不同程度地钻遇较薄的油层,从烃检结果来看,较薄的油层(<3 m)响应特征不明显,最终对7口井目的层段的烃检结果进行了统计,吻合率达到78%。通过地质物探综合研究认为,该区的2、3号块具有一定勘探潜力,储层含油气几率较大。烃检结果显示(图5、图6),预测储层(2号块砂体1、砂体2;3号块砂体3、砂体4、砂体5)无论在剖面还是平面上,都有较好的油气响应特征,并且异常强度与构造相吻合。因此,在该结果的指导下,部署了Y-7及Y-8井,以期得到较好的油气发现。
图4
图4
Y-3井(a)与Y-4井(b)烃检结果剖面
Fig.4
The section of hydrocarbon detection results of well Y-3(a) and Y-4(b)
图5
图5
Y-7井储层剖面与平面烃检结果
Fig.5
The section and slice of hydrocarbon detection results of reservoirs of well Y-7
图6
图6
Y-8井储层剖面与平面烃检结果
Fig.6
The section and slice of hydrocarbon detection results of reservoirs of well Y-8
3 结论
1) 地震资料的品质直接影响叠前油气检测的结果,高质量的叠前道集资料是进行叠前油气检测的基础,因此叠前道集的优化处理至关重要。研究中,流体因子的提取过程需要输入关键的参数——纵横波速度比,这一参数影响流体检测结果的准确性,因此必须根据实际的测井资料进行拟合得到。
2) 在固流解耦思想指导下,通过对叠前道集进行精细处理及叠前反演技术优化,直接提取流体项Δf/f进行储层含油气性检测,流体识别直观性强,与测井结果对应较好,并且落实了渤海Y构造有利含油气分布,为该区井位部署及储量计算提供了依据。
3) 目前在渤海海域应用文中所述叠前反演技术进行储层含油气性检测研究的区块较少,在研究过程中要充分考虑地质因素及储层物性的影响,其是否具有广泛的适用性还需要进行深入的研究。
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频率衰减属性在深层碳酸盐岩油气勘探中的应用
[J].应用频率衰减梯度属性和低频伴影现象相结合进行油气检测的思路。首先介绍了频率衰减梯度和低频伴影现象的方法原理;其次结合研究区长兴组地层的储层物性参数建立地质模型,运用黏滞弥散型波动方程模拟和分析了该类储层的地震响应特征,模型分析表明利用频率衰减梯度属性和低频伴影现象识别此类储层的含气性是可行的。实际资料的应用证实频率衰减梯度属性和低频伴影现象对该类储层都有较好的指示,其预测结果能够相互验证,提高了储层预测及流体检测的准确性,为BL 地区长兴组地层碳酸盐岩礁滩相岩性油气藏及类似油气藏的油气识别及流体检测提供了思路。]]>
Application of frequency attenuation attributes to oil and gas exploration in deep carbonate rocks
[J].Changxing Formation in BL area, this paper put forward a train of thought for hydrocarbon detection which combinedfrequency attenuation attributes and low frequency ad joint-shadow phenomenon. This paper first introduced theprinciple of frequency attenuation attributes and low frequency ad joint-shadow phenomenon; secondly establishedgeological model combined with the reservoir physical parameters of Changxing Formation in BL area, and simulatedand analyzed the seismic response characteristics of the reservoir by using viscosity-diffusivity wave equation. Themodel analysis result shows that it is feasible to detect gas-bearing properties of reservoir by using frequency attenuationattributes and low frequency ad joint-shadow phenomenon. Application of real data demonstrates that frequencyattenuation attributes and low frequency ad joint-shadow phenomenon has good instruction to the reservoir, andimproved the accuracy of reservoir prediction and fluid detection, which can provide a way for oil-gas identification andfluid detecttion of carbonate reef flat lithologic reservoir and similar reservoirs ofChangxing Formation in BLarea.]]>
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