川南页岩气田L区块页岩脆性指数叠前地震定量预测

Quantitative prediction of shale brittleness index in block L of shale gas field in southern Sichuan using pre-stack seismic prediction method

东方地球物理勘探有限责任公司西南物探研究院,四川成都610036

Southwest Institute of Geophysical Exploration,BGP Inc.,CNPC,Chengdu 610036,China

页岩脆性指数是页岩气压裂设计中应考虑的关键参数之一。以川南页岩气田L区块页岩脆性指数研究为例,针对目前常用的弹性脆性预测方法存在地区适应性差的问题,提出了一种多元非线性回归脆性指数预测的改进模型。首先通过模型建立了矿物脆性指数与Rickman脆性指数及最小闭合应力系数之间的关系,然后针对三维地震资料利用叠前地震反演方法获取所需的弹性参数,进而实现研究区页岩层段纵向及横向脆性预测。川南页岩气田L区块的应用结果表明,在已有钻井矿物脆性指数的约束下,利用改进后的脆性指数预测方法得到的改进模型适用性更强,利用该模型预测得到的五峰组—龙马溪组一亚段脆性指数在横向上分布稳定,符合地质认识;通过已知井检验可知,预测得到的脆性指数在纵向上与矿物脆性指数相关性好。

Shale brittleness index is a key parameter in the design of shale gas fracturing.Commonly used elastic brittleness prediction methods have poor adaptability in block L of the Southern Sichuan shale gas field owing to regional differences in tectonic setting and sedimentary characteristics.Although both Rickman brittleness index and minimum closure stress coefficient have a certain correlation with mineral brittleness index,their correlation is not sufficient to accurately predict mineral brittleness index; therefore,a new model of multivariate nonlinear regression brittleness index prediction is proposed in this study.The model establishes the relationship between mineral brittleness index,Rickman brittleness index,and minimum closure stress coefficient and then uses 3D seismic data to obtain the required elastic parameters through pre-stack seismic inversion method to realize the longitudinal and lateral quantitative brittleness prediction of the shale interval in the study area.The application in Block L of the Southern Sichuan Shale Gas Field proves that the new prediction method of brittleness index is more applicable under the constraints of the existing mineral brittleness index of drilled well.The brittleness index of the Wufeng Formation-Longmaxi Formation first sub-member is distributed stably in the horizontal direction,and this is in line with geological understanding.In the vertical direction,the shale brittleness index tends to increase gradually from top to bottom,and the vertical stratification is obvious.This study revealed that drilling data and predicted brittleness index have a good correlation with mineral brittleness index,which has application and promotion value.

中国石油天然气股份有限公司西南油气田分公司勘探开发研究院项目(D3180121PB)资助。

10.3969/j.issn.1000-1441.2023.01.013