地震振幅能量表征河道砂体及其储层物性——以川中地区中侏罗统沙溪庙组为例

四川盆地中部地区中侏罗统沙溪庙组为三角洲前缘沉积,水下分流河道砂体发育,是该区新一轮非常规天然气勘探开发的新领域。为了支撑该区的天然气勘探部署,开展了致密砂岩气勘探开发技术攻关,在河道砂体波动方程正演模拟的基础上,利用多属性融合识别河道砂体边界,结合地震强振幅“亮点”刻画出河道砂体;通过计算出河道砂体振幅能量并与河道砂体储层物性进行相关性分析,预测优质储层分布规律。研究结果表明：①川中地区沙溪庙组8号砂组的地震响应特征为“砂体顶界表现为强波谷、底界表现为强波峰”的“亮点”反射特征,地震剖面表现为沿河道走向砂体连续、稳定分布;②预测该区沙溪庙组8号砂组河道宽度介于600～1 400 m,面积为67.22 km2;③在河道砂岩地震调谐厚度范围内,砂体地震振幅能量与砂体物性具有线性正相关关系,物性越好振幅能量越强,并且随着砂体厚度和孔隙度增加,砂体的地震“亮点”模式更容易识别。结论认为,河道砂体振幅能量与砂体物性相关度超过80%,地震振幅能量能反映河道砂体物性,该认识可以为后续井位部署及非常规天然气勘探开发提供参考。

Characterization of channel sand body and its reservoir physical properties based on seismic amplitude energy: A case study of the Middle Jurassic Shaximiao Formation in the central Sichuan Basin

The Middle Jurassic Shaximiao Formation in the central Sichuan Basin is a delta front deposit with developed underwater distributary channel sand body, and it is a new field of unconventional gas exploration and development in this area. In order to support the deployment of natural gas exploration in this area, this paper researched the key technologies for the exploration and development of tight sandstone gas. Based on forward modeling of the wave equation of channel sand body, the boundary of the channel sand body was identified by means of multi-attribute fusion, and then combined with the "bright spot" of strong seismic amplitude, the channel sand body was depicted. Finally, the distribution law of high quality reservoir was predicted by calculating the amplitude energy of channel sand body and analyzing the correlation with the reservoir physical property of channel sand body. And the following research results were obtained. First, No.8 sand body combination of Shaximiao Formation in this area presents continuous and stable distribution along the strike direction of river channel in the seismic profile, and its seismic response characteristics are "bright spot" reflection characteristics of "strong wave trough at the top boundary of sand body and strong wave peak at the bottom boundary". Second, it is predicted that the channel in No.8 sand body combination of Shaximiao Formation in this area is 600–1 400 m in width and 67.22 km2 in area. Third, in the range of the seismic tuning thickness of channel sandstone, the seismic amplitude energy of sand body is in a linear positive correlation with its physical property. The better the physical property is, the stronger the amplitude energy is. As the thickness and porosity of the sand body increase, it is easier to identify the seismic "bright spot" pattern of the sand body. In conclusion, the amplitude energy of channel sand body is more than 80% correlated with the physical property of sand body, and can reflect the physical property of channel sand body. This research result can provide reference for subsequent well location deployment and exploration and development of unconventional natural gas.