Seismic Velocity Study and Application Constrained by Sequence Stratigraphy Framework-A Case Study on the SN21 Well Area, Junggar Basin, China

In this paper, we present a case study where we combine sequence stratigraphiy with seismic velocity study for a 3D seismic survey landing at the SN21 well area in Junggar Basin, China.The main trap in this area is subtle composite trap of structure and lithology.Our purpose is to provide essential maps for demonstrating well location by predicting reservoir's lateral distribution and its depth.Firstly, according to the principle of sequence stratigraphy and the correlation analysis of well logs and seismic data, we constructed high-resolution stratigraphic frameworks in this subtle-reservoir area.Each framework has its given geological meaning.The three main frameworks are CX0 (reflection of QSH top), CX3 (reflection of TTH top), and CX5 (reflection of TTH bottom).Secondly, by using ray tracing techniques, we merged these sequence stratigraphic frameworks with the seismic rms velocities, as well as controlled logging and geological constraints, to estimate seismic interval velocity model of these stratigraphic frameworks.Study results demonstrate that, within target strata (CX0-CX3), the south and southeastern sand distribution area shows high velocity values, while the north mudstone low velocity values.The magnitude of velocity reflects the sand content.Study results also prove that the seismic velocity and the seismic amplitude attribute corroborates each other in predicting sand distribution.Furthermore, the estimated final velocity model for time to depth conversion has few systemic and random errors, and the predicted structure maps with this velocity model turn out to be of relatively high precision and coincide with the subsequent drilling data.