四川盆地营山构造自流井组页岩油层小断层和裂缝高分辨率地震预测

High-resolution seismic prediction of small faults and fractures in shale oil reservoirs of Ziliujing Formation of Yingshan structure in Sichuan Basin

应用常规地震裂缝预测技术对四川盆地营山构造自流井组页岩发育的小断层和裂缝进行预测,存在预测精度低、预测结果多解性强等问题。为解决小断层和裂缝高分辨率预测问题,提出沿层属性变化率小断层和裂缝预测方法。结果表明:该方法在页岩油层层状结构连续沉积特征情况下,基于地震资料开展叠后/叠前弹性属性反演,获得纵波阻抗、横波阻抗、纵横波速度比、密度等岩石弹性属性;通过地质力学属性建模,获得坍塌压力、破裂压力、弹性模量和泊松比等地质力学属性;按构造形态将弹性属性或地质力学属性划分出纵向多个小层后,评价多地震道间弹性属性和地质力学属性的相似性,得到高于地震资料分辨率的预测成果。四川盆地营山构造自流井组页岩油探井实钻和压裂评价结果验证了小断层和裂缝预测成果,证实了该方法的有效性。研究成果为页岩油层精细评价、井位部署、压裂工艺优化等工作提供技术支撑。

Conventional seismic prediction techniques applied to predict small faults and fractures developed in shale of Ziliujing Formation in Yingshan structure in Sichuan Basin have problems of low prediction accuracy and high ambiguity in prediction results.In order to achieve high-resolution prediction of small faults and fractures,pre-diction method of along-layer attributes variation rate is proposed for small faults and fractures.The results show that,in the case of shale oil reservoirs with laminar structure and continuous deposition characteristics,post-stack/pre-stack elastic attribute inversion is carried out based on seismic data to obtain rock elastic attributes including P-wave impedance,S-wave impedance,P-S wave velocity ratio and density.Geo-mechanical attributes including col-lapse pressure,fracturing pressure,elastic modulus and Poisson’s ratio are obtained by geo-mechanical attributes modeling.After dividing elastic attribute or geo-mechanical attribute into several sub-layers vertically according to structural geometry,the similarity of elastic attribute and geo-mechanical attribute among several seismic traces is evaluated,obtaining prediction results higher than seismic data resolution.Drilling and fracturing evaluation of shale oil exploration wells in Ziliujing Formation of Yingshan structure in Sichuan Basin verify the prediction results of small faults and fractures,confirming the effectiveness of this method.The research provides technical support for fine evaluation,well deployment and fracturing technique optimization of shale oil reservoirs.