东海致密气藏AVO反射特征及其在储层预测中的应用

东海油气田目的层埋藏深,非均质性强,为致密含气砂岩储层,叠后地震属性刻画储层展布难度大,需利用叠前信息提高储层预测的精度。研究了AVO储层预测原理和可行性,通过地震正演分析了含气性、孔隙度及砂岩厚度对AVO特征的影响,并总结截距和梯度等属性的变化规律,运用存储滤波技术一步完成-90°相位转换和分频解释工作,得到用于岩性预测的相对泊松比属性体。以西湖凹陷中南部某中深层致密砂岩气田为例,通过相对泊松比属性分析砂体的展布特征,优化水平井水平段的位置,钻探结果与预测结果吻合较好,水平段实现了100%的砂岩钻遇率。结果表明,利用致密砂岩气的AVO特征、采用基于AVO属性的存储滤波技术可提高东海深层致密砂岩储层的预测精度。

AVO reflection characteristics of the tight gas reservoir and its application in the reservoir prediction of the East China Sea

The target reservoirs of the oil-gas field in the East China Sea are characterized by deep buried depth and serious heterogeneity, which are the tight gas-bearing sandstone reservoirs and difficult to describe for the reservoir distribution with the help of the poststack seismic attribute, therefore the prestack information is needed to enhance the precision of the reservoir prediction. The principle and feasibility of AVO reservoir prediction were studied, by means of the seismic forward modeling, the influences of the gas-bearing property, porosity and sandstone thickness on the AVO characteristics were analyzed, and moreover the change laws of the intercept and gradient attributes etc. were summarized,by storage filtering technique, the -90° phase conversion and frequency division interpretation were completed to obtain the relative Poisson ratio attribute for the lithology prediction. Taking the middle-deep tight sandstone gas fields in the south-central parts of Xihu Sag as an example, with the help of the relative Poisson’s ratio attribute, the characteristics of the sandbody distribution were analyzed, the location of the horizontal section of the horizontal well was optimized. The drilled results have much better coincidence with the predicted achievements, thus 100% sandstone drilling rate was realized for the horizontal interval. The results show that by the AVO characteristics of the tight sandstone gas and furthermore the storage filtering technique based on the AVO attribute, the predicted precision of the deep tight sandstone reservoirs in the East China Sea can be improved.