鄂尔多斯盆地上古生界地层AVO技术的应用
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摘要
AVO技术是利用振幅随炮检距 (或入射角 )变化的规律 ,求取地下地层的岩性信息。鄂尔多斯盆地是典型克拉通盆地 ,构造平缓 (倾角不到 1°) ,断层不发育 ,非常适用 AVO理论假设反射层为水平层这一基本条件。根据工区的地震地质特征 ,在 AVO分析的基础上 ,应用钻井地质、测井资料设计的模型 AVO正演及反演的研究 ,总结了一套在现有地震分辨率条件下的鄂尔多斯盆地上古生界储层 AVO响应特征。即 :无论砂岩储层是否含气 ,其底部反射振幅随入射角增加均会出现从强到弱—极性反转—从弱到强的现象 ,只是反转的角度有所差异 ;在梯度剖面上 ,含气砂岩与不含气砂岩的亮点特征差异较大。据此响应特征预测了有利的储集区。
AVO technique is based on amplitude changing with incident angle to get lithologic information of subsurface strata.The technique is very useful during early and middle stages of prospecting because only seismic data are processed and drilling and logging data are not needed. The Ordos basin is a typical craton basin,which has a gentle structure(less than 1° in dip) and undeveloped faults,and therefore satisfies the basic condition that reflectors are supposed to be horizontal by AVO theory.However,target strata in the area also have some other characteristics such as deep buried depth(over 2 500 m),small thickness(a single sand layer is usually less than 10 m in thickness)and repeated alternations of mud and sand layers.And the strata belong to thin layer extent in the case of the existing seismic wavelet resolution(dominant frequency is 30 Hz).In such conditions,the observed AVO phenomenon is only a coordinating result of multiple thin alternations rather than a reflection of a single interface and thus cannot be explained mechanically by AVO character for a single interface.Therefore,if we use AVO technique to predict reservoirs in upper Palaeozoic strata in the area,we must start from the already known drills and take AVO forward model as the tool to analyze AVO characteristics of the thin alternations and to find out AVO attributes that are sensitive to lithologic characters.In this way,we can recognize and predict reservoirs correctly. The authors have worked out a series of AVO response characteristics to reservoirs in upper Palaeozoic strata in the Ordos basin according to seismogeologic features of the area as well as AVO forward and inverse models designed by drilling and logging data.Namely,whether or not a sandstone reservoir is gas bearing,its bottom reflection amplitude increasing with incident angle will go from strong to weak,then polarity reversal and then from weak to strong,and only there is some differences in reversal angles;and there are great differences in bright spot characteristics between gas bearing and no gas sandstones.
AVO technique is based on amplitude changing with incident angle to get lithologic information of subsurface strata.The technique is very useful during early and middle stages of prospecting because only seismic data are processed and drilling and logging data are not needed. The Ordos basin is a typical craton basin,which has a gentle structure(less than 1° in dip) and undeveloped faults,and therefore satisfies the basic condition that reflectors are supposed to be horizontal by AVO theory.However,target strata in the area also have some other characteristics such as deep buried depth(over 2 500 m),small thickness(a single sand layer is usually less than 10 m in thickness)and repeated alternations of mud and sand layers.And the strata belong to thin layer extent in the case of the existing seismic wavelet resolution(dominant frequency is 30 Hz).In such conditions,the observed AVO phenomenon is only a coordinating result of multiple thin alternations rather than a reflection of a single interface and thus cannot be explained mechanically by AVO character for a single interface.Therefore,if we use AVO technique to predict reservoirs in upper Palaeozoic strata in the area,we must start from the already known drills and take AVO forward model as the tool to analyze AVO characteristics of the thin alternations and to find out AVO attributes that are sensitive to lithologic characters.In this way,we can recognize and predict reservoirs correctly. The authors have worked out a series of AVO response characteristics to reservoirs in upper Palaeozoic strata in the Ordos basin according to seismogeologic features of the area as well as AVO forward and inverse models designed by drilling and logging data.Namely,whether or not a sandstone reservoir is gas bearing,its bottom reflection amplitude increasing with incident angle will go from strong to weak,then polarity reversal and then from weak to strong,and only there is some differences in reversal angles;and there are great differences in bright spot characteristics between gas bearing and no gas sandstones.
引文
[1] 刘雯林,甘利灯.中国东部地区油气层的AVO检测标志[J].石油物探,29(4),1990,1-11.
[2] 吴志强,丁国栋.CDP道集内的AVO效应及其对岩性处理的影响[J].石油物探,39(4),2000,87-95.
[3] 史占祯,金蕙,张静华,蔺洁,等.AVO与天然气工业.天然气勘探,1997(增刊),36-43
[2] 吴志强,丁国栋.CDP道集内的AVO效应及其对岩性处理的影响[J].石油物探,39(4),2000,87-95.
[3] 史占祯,金蕙,张静华,蔺洁,等.AVO与天然气工业.天然气勘探,1997(增刊),36-43
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