Seismic Prediction of Tight Oil Sweet Spots in Fuyu Formation of Sanzhao Sag, Songliao Basin

A great potential tight oil resources are developed in the Lower Cretaceous Quantou Formation in the northern part of the Songliao Basin. Longitudinal sand body staggered distribution, thin single layer thickness and rapid lateral change make it difficult to meet the requirements of tight oil sweet spots prediction by using post-stack inversion and seismic attributes analysis. This paper proposes a set of seismic techniques for predicting the Fuyu tight oil sand bodies, porosity, oil-bearing property and fractures by using pre-stack geostatistical inversion methods. First, petrophysics analysis of logging data is carried out and a single lithology identification factor is proposed to distinguish sandstone and mudstone perfectly by combining Young's modulus and Poisson's ratio. The cross plot analysis of elastic parameters makes it clear that the P-wave impedance has a high correlation with porosity and P⁃S wave velocity ratio has a high correlation with oil saturation. Next, the P-wave impedance, P⁃S wave velocity ratio and density can be acquired by using the pre-stack geostatistical inversion technology, which can be transformed to the single lithology identification factor to predict the distribution of sand bodies, moreover, the porosity and oil-bearing property can be inversed through pre-stack geostatistics co-simulation. Then, the combination of large and medium-scale fractures predicted by post-stack maximum likelihood attribute and small-scale fractures predicted by pre-stack azimuthal anisotropy inversion can comprehensively predict fractures distribution of the target interval. Finally, all the above techniques are applied to achieve high-precision prediction of tight oil sweet spots and effectively guide the deployment and trajectory orientation of horizontal wells in Yuxi work area of Sanzhao sag.