建南地区须四段致密气层AVO响应特征——以新店1井为例

AVO response characteristics of tight-gas reservoir of the 4^(th) section ofXujiahe formation in Jiannan area:a case study of Xindian Well 1 (XD1)

为理清建南地区须四段致密砂岩气层振幅随偏移距变化(amplitude variation with offset,AVO)响应特征,为储层的叠前反演工作提供指导,以该区新店1井实际资料为例进行AVO正演模拟分析,通过流体替代、泥质替换和变厚度模拟来分析几种主要储层参数的变化对AVO响应的影响特征。实际井的测井响应和AVO模拟分析指出,须四段气层主要表现为Ⅳ类含气响应特征,气层的含气饱和度、孔隙度、泥质体积分数和厚度参数的变化对该含气响应会产生一定规律特征的差异性影响:含气饱和度的增大使AVO截距P减小,斜率G先减小后增大,且含气饱和度在0~20%期间最为明显;孔隙度的增大使截距P减小,斜率G增大,振幅极性由正变负,含气响应类型由Ⅱ类到Ⅲ类向Ⅳ类转化;泥质体积数的增大使截距P、斜率G均增大,P值的变化幅度较G值大;气层厚度的增大使P值缓慢变小,G值减小且幅度较大。参数对比结果表明,孔隙度变化的影响最大,泥质体积分数次之,含气饱和度最小;储层厚度变化的影响特征符合Widess分辨率原则,可为AVO分析识别薄气层提供有利依据。

In order to provide guidance to reservoir prestack inversion,It is necessary to clarify amplitude variation with offset(AVO)response characteristic of tight gas reservoir of the 4 th section of Xujiahe formation in Jiannan area.Therefore,the AVO forward modeling analysis was carried out with the actual data of Xindian Well 1 in this area as an example via fluid replacement,mud replacement and variable thickness simulation to analyze the varying influence of main reservoir parameters on AVO response characteristics.The actual well logging response and AVO modeling analysis express that,the gas reservoir in the 4 th section of Xujiahe formation mainly show the classⅣgas response characteristics and variation ofreservoir parameters such as gas saturation,porosity,clay content and thickness have disparative influence on certain regular features on gas response,which are:AVO intercept P decreases and gradient G decreases initially and then increases as gas saturation increases,in which its variation is obvious as gas saturation vary from 0 to 20%;Intercept P decreases and gradient G increases as porosity increases,in which the amplitude polarity vary from positive to negative,and gas response type transform from ClassⅡto ClassⅢup to classⅣ;Intercept P and gradient G increase as the clay content increases,and variation amplitude of intercept P is bigger than that of gradient G;Intercept P decreases slowly and gradient G decreases sharply as the thickness of reservoir increases.Comparison of above parameters show that,variable porosity have maximum influence,while clay content and gas saturation will in turn have minimum influence;The influence of variable reservoir thickness in accordance with Widess resolution principle,can provide the useful basis for the identification of the thin layer by AVO analysis.