基于地震沉积学原理的河道砂体精细刻画——以四川盆地龙岗地区沙溪庙组致密气藏为例

Precise depicting channel sandbodies based on seismic sedimentology: An example from tight gas reservoirs of Shaximiao Formation, Longgang area, Sichuan Basin

四川盆地中部的龙岗地区中侏罗统沙溪庙组一段为一套滨浅湖—三角洲平原亚相沉积物,河道砂体广泛发育。早期地震预测成果对该区河道砂体的识别效果不佳,河道轮廓及形态不清晰,薄层砂体识别困难。因此,开展了基于地震沉积学原理的河道砂体精细刻画:①对零相位的三维地震资料开展90°相位转化以实现地震同相轴与岩性地层的基本对应;②在目的层优势频带范围内开展分频处理,以获得代表不同调谐厚度砂体的调谐数据体;③利用地层切片和分频颜色融合技术来实现分流河道的平面刻画。结果表明:①对原始地震数据开展90°相位转化,地震同相轴与砂体中心相对应,可以更为真实反映砂体发育的空间位置;②分频解释技术可以有效提高薄层砂体的识别能力,使砂体的纵向分辨能力达到λ/8的分辨极限;③与早期的河道刻画成果相比,地层切片方法可以有效降低平面切片的穿时效应,利用不同主频调谐体的地层切片开展分频颜色融合,提高了河道的平面成像效果。

The Middle Jurassic Shaximiao 1 Member, Longgang area, central Sichuan Basin, is a set of sediments of shore-shallow lake-delta plain subfacies with extensively developed channel sandbodies. Based on previous seismic prediction, these sandbodies are not identified well, the outlines and morphologies of the channels are not made clearly, and the sandbodies in thin layers cannot be distinguished easily. So, a precise depicting channel sandbodies based on seismic sedimentology was carried out. Firstly, 90° phase transformation was conducted on the 3D seismic data of 0° phase to realize the basic correspondence between seismic event and lithostratigraphy. Secondly, frequency-division treatment was carried out in the range of dominant frequency band of the target layer to obtain the tuning data volume which can represent the sandbodies with different tuning thicknesses. Thirdly, distributary channels were characterized in plane by means of stratigraphic slice and frequency-division color blend technique. Results show that,(1) by conducting 90° phase transformation on the original seismic data, the seismic event corresponds to the center of the sandbody, so that the spatial position of sandbody development can be reflected truly;(2) the frequency-division technique can effectively improve the capacity of identifying sandbodies in thin layers, so that the vertical sandbody resolution capacity can be up to the resolution limit of λ/8;and(3)compared with previous channel characterization, the stratigraphic slice method can effectively reduce the diachronic effect of plane slice, and it adopts the stratigraphic slices of different dominant frequency tuning cubes for frequency-division color blend to improve the plane imaging effect of channels.