弹性波阻抗理论和实现方法

1、弹性阻抗理论,hampson-russell软件实现弹性波阻抗反演,2020/7/9,弹性阻抗,介绍,先回顾弹性阻抗反演的原理,然后利用hampson-russell 一组软件分析弹性阻抗反演一个实际例子. 弹性阻抗elastic impedance (ei) 是由bp 公司patrick connolly 提出. 实现弹性阻抗反演可用avo和strata软件自然组合来完成. 在谈论弹性阻抗反演之前, 简单回顾反演方法在地震勘探运用的历史.,2020/7/9,弹性阻抗,cdp/crp道集,迭加,反演,估算 z= vp,地震岩性估算,传统的地震岩性估算是在地震数据叠加偏移后数据(叠后数据)道进行

2、反演. 这只能估算声阻抗, 不足于推测流体成分.,2020/7/9,弹性阻抗,道集,叠加,反演,avo 分析,属性 1,属性 2,估算 vp, vs, 和 ,估算 z= vp,avo 方法 同时使用多属性估算vp, vs, 和 , 可估算推测流体和岩性.,2020/7/9,弹性阻抗,avo分析可能用的属性,但是哪两种(或更多属性)可用来最好地预测流体和岩性这些参数? 目前avo可提取和使用的一系列不同属性: 偏移距或角度段限(范围限制)叠加 弹性阻抗反演 截距和梯度 提取的纵横波反射系数 rp,rs 由 rp 和 rs 反演到纵横波阻抗 zp, zs 纵横波阻抗 zp, zs 转换lambda

3、-mu-rho 分析 本讨论先使用前面两个属性的方法. 后面再讨论其它的属性方法.,2020/7/9,弹性阻抗,范围限制叠加,道集,avo 分析,近叠加,远叠加,以上是范围限制叠加的简单流程. 利用常偏移距或常角度的范围叠加已经非常成熟. 问题是如何解释其结果?,2020/7/9,弹性阻抗,(a),(b),近角度 (0o-15o) 叠加 远角度 (15o-30o)叠加 数据来自加拿大colony 区 块. 在630ms有一个“亮点” 震幅在远角度 叠加上比近角 度叠加要强的多. 从井资料 分析这是气砂岩导致 “亮点”.,气砂岩范围限制叠加,2020/7/9,弹性阻抗,这是近远偏移距(角度)的交

4、绘图,高震幅区块用不同颜色突出显示.,角度叠加进行交绘图,2020/7/9,弹性阻抗,这是交绘图中的突出区块对应在剖面上的位置. 可看出气砂岩已被很好地描绘.,2020/7/9,弹性阻抗,(a) 近角度叠加 (0-15o)时间切片, (b)远角度叠加 (15-30o)时间切片(三维河道砂). 对时间切片震幅包络求得是10ms窗口内的平均值并运用了z-score转换. 异常河道砂得以清楚显示.,角度范围叠加,(a),(b),2020/7/9,弹性阻抗,从范围限制叠加到弹性阻抗,范围限制叠加使用的是常偏移距或常相位道集,方法很成熟并可避免同相轴未拉平问题. 但它究竟有何含义? patrick co

5、nnolly(bp), 提出新颖的方法来解释范围叠加的含义, 称之为弹性阻抗. 弹性阻抗是基于aki-richards 等式, 下几张图片解释弹性阻抗的概念和由来.,2020/7/9,弹性阻抗,弹性阻抗理论,aki-richards 等式可写为(三项式) :,connolly (1999)提出, 类似于声阻抗, 我们定义弹性阻抗(ei) 为:,2020/7/9,弹性阻抗,假设,注意到,我们可以把 aki-richards 等式重写为:,假设 k 为常数, 可以将上式写为:,2020/7/9,弹性阻抗,然后进行积分和取幂, 可得到以下弹性阻抗 ei等式:,如果 = 0o, ei 弹性阻抗就还原为

6、声阻抗(ai), 等式为:,2020/7/9,弹性阻抗,以上等式使用的是aki-richards所有三项等式. 对于入射角大于300, 该等式将不是线性的拟合. 对于大角度 (大偏移距), 如果只用等式的前两项,等式可写为:,当 = 0o, 得到:,2020/7/9,弹性阻抗,将声阻抗(ai)转换入射角为30 的弹性阻抗通常曲线类似但阻抗绝对值变低. 角度增加其视声波阻抗降低. 油砂岩比页岩视声波阻抗降低幅度更大.如下图,connolly 1999,弹性阻抗 油饱和度的影响,2020/7/9,弹性阻抗,弹性阻抗 实例,下图 显示声阻抗和弹性阻抗(30度角)的曲线比较:,2020/7/9,弹性阻

7、抗,重叠显示更好地区分弹性阻抗和声阻抗在含油砂岩处的差别:,2020/7/9,弹性阻抗,ei 反演步骤,道集,avo 分析,近角度叠加q1,远角度叠加q2,反演弹性阻抗 ei(q1),反演弹性阻抗 ei(q2),2020/7/9,弹性阻抗,case study from the colony sand play in alberta, canada,2020/7/9,弹性阻抗,applying elastic impedance to the colony data,in this exercise, we will start with the 2d colony dataset which

8、 we analyzed earlier and apply the elastic impedance analysis to it.,first re-open the avo_class database in geoview. on the geoview window, click on database / open. select avo_class.wdb from the pulldown list, as shown, and click on ok:,2020/7/9,弹性阻抗,on the geoview main window, click on the avo /

9、avo button to restart the avo program:,select the option to open previous project and choose the colony.prj project:,2020/7/9,弹性阻抗,before analyzing the data, we will create the elastic impedance logs in the modeling window. if it is not visible, click on the modeling / single well button on a seismi

10、c window and select avo_well on the open well menu to get the following window :,2020/7/9,弹性阻抗,next, click on the logs / transforms button as shown on the left, and select the elastic impedance option from the transforms menu shown below:,2020/7/9,弹性阻抗,click next on the transforms menu and select th

11、e correct well (avo_well) for the p-and s-wave logs and for storing the elastic impedance log, as shown below.,2020/7/9,弹性阻抗,on the next menu, make sure the frm edited logs are used for the calculation of the elastic impedance and call the result ei_near as shown.,2020/7/9,弹性阻抗,click on next and fil

12、l in the next menu as shown, choosing constant angle and filling in an angle of 7.5 degrees.,2020/7/9,弹性阻抗,when the ei_near log has been created, select the logs / transforms option again, and fill in the menus as shown previously except for the last two menus shown here. on these menus, create a ne

13、w log called ei_far (making sure that the frm edited logs are used in the calculation) at a constant angle of 22.5 degrees.,2020/7/9,弹性阻抗,to display the two elastic impedance traces together, click on the “eyeball” icon to bring up the parameter menu. under the layout tab, turn off the display only

14、active logs button to see all of the logs, and put the ei_near and the ei_far logs on the same track, as shown.,2020/7/9,弹性阻抗,click on ok and you will see the display below. notice that the ei_far log plots to the left in the gas zone and to the right in the rest of the log. now, lets crossplot thes

15、e two logs.,2020/7/9,弹性阻抗,click on crossplot and fill out the menu as shown below, selecting the elastic impedance log type as well as and .,then, click on next .,on this menu, select the well, and click on next .,2020/7/9,弹性阻抗,on this menu, select elastic impedance for both the x and y axes, and ch

16、ange the plot title as shown below. (note that we will select a different elastic impedance log for each axis on the next menu). click on next .,2020/7/9,弹性阻抗,on this menu, select ei_near for the x axis and ei_far for the y axis, as shown. click on next .,on this menu, select time as the domain, wit

17、h start and end values of 600 and 675. click on ok to get the crossplot.,2020/7/9,弹性阻抗,notice that the axes of the plot are both labeled the same. to change the annotation, click on edit / annotations and change the menu as shown on the right:,click on ok and the plot will appear as shown on the lef

18、t. notice the clear separation of the points on the lower left of the plot.,2020/7/9,弹性阻抗,let us now perform zone analysis to see if the anomaly seen on the crossplot really is the gas sand. to do this, first display the well log curves by clicking on the cross-section button. after using the zoom o

19、ption, you should see a plot similar to this:,2020/7/9,弹性阻抗,now, click on the zones / add option and create the elliptical grey background trend as shown on the right.,2020/7/9,弹性阻抗,now define the elliptical yellow gas trend as shown.,2020/7/9,弹性阻抗,note that the plot of the well logs has been update

20、d with the colors, and the anomalous points do indeed correspond to the gas sand zone.,2020/7/9,弹性阻抗,now go to the window containing the original cdp gathers. click on process / stack / range limited stack:,2020/7/9,弹性阻抗,use the defaults on the first menu as shown on the right, and click on next .,t

21、hen, fill in the second menu as shown on the left. notice that we are creating 2 angle stacks from 0 to 30 degrees.,2020/7/9,弹性阻抗,the two angle stacks are created as shown here, where range_limit_stack is the near angle stack, and range_limit_stack2 is the far angle stack.,2020/7/9,弹性阻抗,select the f

22、ile called range_limit_stack.vol from the menu and click on open.,next, click on the strata button on the geoview main window. we will continue using the colony project, as indicated in the menu on the right.,click on ok to bring up the strata main window, and then click on data manager / import dat

23、a / open seismic / open from project.,2020/7/9,弹性阻抗,fill out the well to seismic map menu as shown and click ok.,the strata window now looks like this:,2020/7/9,弹性阻抗,click on horizon / pick horizons and pick a second event, as shown. horizon 1 is the trough at the top of the gas sand.,2020/7/9,弹性阻抗,

24、finally, pick a third event, as shown here. then click ok to finish the picking.,2020/7/9,弹性阻抗,next, click on model / build/rebuild a model. fill in the first page as shown on the right, changing the option to: typical setup of elastic impedance for far-offset stack inversion. click on next .,on the

25、 third page, select the well avo_well and click next .,2020/7/9,弹性阻抗,on the next page, we must select the elastic impedance log which corresponds to the near angle stack. since this stack covers an angle range of 0 to 15 degrees, choose ei_near, calculated for the angle of 7.5 degrees.,now click on

26、next twice and ok to build the model.,then, click on invert / model based as shown:,on the first page, change the output file name to near_inversion. click on next twice.,on the third page, change the average block size to 4. click ok to run the inversion.,2020/7/9,弹性阻抗,the inversion result will loo

27、k like this:,2020/7/9,弹性阻抗,next, click on window / new window to create an emptystrata window. in this new window, click on data manager / import data / open seismic / open from project and select range_limit_stack2.vol, as shown on the right. click on open to get the result shown below. notice that

28、 the existing picks are annotated.,2020/7/9,弹性阻抗,next, click on model / build/rebuild a model and select the option typical setup of elastic impedance for far-offset stack inversion on the first page, as done previously. select avo_well on the third page and choose the ei_far log (22.5 degrees) on t

29、he fourth, as shown. the new model will look like this (you may need to update the color key):,2020/7/9,弹性阻抗,next, click on invert / model based and change the name of the output volume on the inversion menu as shown below.,on the third page, change the average block size to 4 and click on ok to sta

30、rt the inversion process:,2020/7/9,弹性阻抗,we now have two inversion results. note that we have had to use two different color scales, since the impedance values are scaled differently.,near_inversion,far_inversion,2020/7/9,弹性阻抗,now let us compare the near-angle inversion with the far-angle inversion b

31、y cross-plotting the two volumes.,on either of the two inversion results, click on process / cross plot:,on the first menu page, select the cdp range from 300 to 360 and the two volumes as shown:,click next until you reach the fourth page. specify a constant time of 630 ms as shown:,2020/7/9,弹性阻抗,if

32、 there were no avo effects, we would expect the far and near impedances to be related by a straight line. in other words, there would be a single cluster. lets add some zones to the crossplot and view the cross-section to see where these zones lie. click on zones / add:,2020/7/9,弹性阻抗,make the first zone using an ellipse and place it along the main axis, as shown. press the apply button to save this zone.,2020/