含气等厚薄互层在弹性介质下的AVO响应  

AVO response on gas-bearing thin interbeds with equal thickness through elastic media

作　　者：吕乐 张航[1] 任根生 Lv Le;Zhang Hang;Ren Gensheng(Northeastern Sichuan Gas District,PetroChina Southwest Oil&Gasfield Company,Dazhou,Sichuan 635000,China)

机构地区：[1]中国石油西南油气田公司川东北气矿,四川省达州市635000

出　　处：《天然气勘探与开发》2022年第S01期9-12,共4页Natural Gas Exploration and Development

摘　　要：针对沉积地层中复杂砂泥岩薄互层中的AVO响应研究寥寥无几。由于利用声学介质进行正演模拟会出现“假响应”情况,故采用弹性介质进行正演模拟,再利用有限差分弹性波动方程对等厚砂泥岩薄互层进行数值模拟,通过层数以及薄层厚度的改变来获取AVO响应特征。经薄互层AVO特征与互层数之间的关系研究发现:(1)受砂泥岩互层单层层厚以及层数的双重调谐效应的影响,当砂泥岩模型单层截距和梯度均大于1/8λ,而层厚小于1/8λ时,顶面AVO效应受薄互层影响有所增强。但当厚度介于1/8λ~1/4λ时,AVO效应反之;(2)极值方面,等厚韵律型薄互层调谐振幅和梯度的最大值均不会超过单层砂岩处于1/4λ处的极大值;(3)结合单层砂体厚度、薄互层层数和孔隙度综合考虑,在薄互层地区,利用PG划分储层时,左上区域是相对有利的含气薄互层区域。So far,very rare study on amplitude versus offset(AVO)response has been conducted for complex thin sand-shale interbeds.Thus,a forward simulation through elastic rather than acoustic media was done because of pseduo response emerged in the latter.And then,a numerical simulation on thin sand-shale interbeds with equal thickness was finished through finite-difference elastic wave equation.Finally,some characteristics on AVO response were attained in the light of the variations of both interbed quantity and thickness.Results show that(1)since AVO is impacted by a double-tuning effect of both single interbed thickness and interbed quantity,this impact may be advanced to some extent when zero-incident amplitude(also so-called intercept)and AVO gradient in the sand-shale model are larger than 1/8λand interbed thickness is smaller than 1/8λ,otherwise a decreasing response at interbed thickness ranging from 1/8λto 1/4λ;(2)the maximums of both tuning amplitude and AVO gradient in rhythmical thin interbeds with equal thickness are not more than those of single-layer sand at 1/4λ;and(3)with consideration of the thickness in single sandbody,interbed quantity,and porosity,the top left of the third quadrant in P-G crossplot is believed as a better area developed with gas-bearing thin interbeds.

关 键 词：砂泥岩薄互层 AVO响应 有限差分弹性波动方程 双重调谐效应 交会图第三象限 

分 类 号：P618.13[天文地球—矿床学] P631.4[天文地球—地质学]