厚层低渗气藏“甜点”预测——以东海陆架盆地西湖凹陷Z气田花港组为例

Sweet spot prediction in thick gas reservoirs with low permeability in Huagang Formation of Z gasfield in Xihu Sag,East China Sea Shelf Basin

东海陆架盆地西湖凹陷厚层(200 m)低渗气藏资源潜力大,“甜点”预测是其高效开发的关键,但是储层非均质性强,“甜点”预测难度较大。为此,建立了厚层低渗气藏不同类型细分“甜点”的地球物理预测技术及方法。首先在“甜点”分类的基础上,开展岩石物理分析及地震正演模拟,明确“甜点”的敏感岩石物理参数及地震响应特征;然后针对不同类型的“甜点”优选合适的叠前弹性反演方法,预测其空间展布特征。研究结果表明:利用纵波模量直接反演可以较好地表征Ⅰ类“甜点”,拟纵横波速度比反演可以较好地表征Ⅱ类“甜点”;开发井钻前“甜点”预测厚度与实钻厚度吻合率较高,Ⅰ类“甜点”达80%以上,Ⅱ类“甜点”达70%以上。该“甜点”预测方法可靠、精度较高,对相似气田开发具有一定的借鉴意义。

The Xihu Sag of the East China Sea Shelf Basin is an area with great potential for exploring thick gas reservoirs with low permeability.The prediction of sweet spots is the key to the development of the reservoir.How-ever,it is difficult to predict sweet spots of thick reservoirs with strong heterogeneity.The geophysical prediction technology and methods of different types of sweet spots are established for offshore thick gas reservoirs with low permeability.Firstly,based on the classification of sweet spots,rock physics and seismic forward modeling analyses are carried out to clarify the sensitive rock physics parameters and seismic response characteristics of sweet spots.Then,the appropriate pre-stack elastic inversion methods are selected to predict the spatial distribution of different types of sweet spots.The research results show that sweet spots of class I can be well characterized by direct inversion of P-wave modulus,and sweet spots of class Ⅱ can be well characterized by pseudo P-and S-wave velocity ratio inversion.The predicted thickness of the sweet spot before drilling is highly consistent with the actual drilling thick-ness of the development well.In addition,the coincidence rate of the sweet spot of class I is more than 80%,and that of class Ⅱ is more than 70%.In conclusion,the method for sweet spot prediction is effective and highly accurate,and it has certain reference significance in the development of similar gas fields.