Classification Of Seismic Waveform And Analysis Of Depositional Facies For The Second And Third Members Of The Shahejie Formation In Shenxian Sag

Shenxian sag is a small petroliferous basin, which is located in the southern of Jizhong depression. Although a lot of exploration results have been made in the past 40 years, there is a big controversy about the genesis, type, characteristics and distribution of depositional facies in different areas and it is obscure about how the structure controlled deposition. Therefore, it can provide sedimentological foundation for further exploration to study the depositional facies of the second and third members of the Shahejie Formation (Es2 and Es3) and understand the types, control factors and space-time evolution of them in different areas.Guided by the high-resolution sequence stratigraphy and reservoir sedimentology, on the basis of core, well logging and 3D seismics, applying Stratimagic waveform seismic facies analysis, the technology of seismic horizon interpretation and facies analysis, the depositional facies of Es2 and Es3 was studied and the following results were obtained in the thesis:Firstly, this paper studied the sequence stratigraphy for Es2 and Es3 in the study area, and established stratigraphic framework. Es3 was divided into three third-order sequence and Es2 was one third-order sequences. Plane distribution and vertical evolution characteristics of depositional facies for intended intervals was analyzed in third-order sequence. In the plane, many fan deltas were developed in abrupt slope, which were small and numerous; braided delta was developed in gentle slope, whose distribution range was wide. In vertical direction, water invasion was the characteristic in Es3 and delta front deposition was wide; filling and leveling up was the characteristic in Es2 and delta plain deposition was dominant.Secondly, basing on regional geological features in the intended area, using Stratimagic software to classify waveforms of four intervals, initial waveform classification maps according with geology law were obtained. On this basis, in the light of the similarity of normative model traces, normative model traces were reclassified and final waveform classification maps were drew. Taking Sp, Rt and log data to calibrate them, the conversion relationship between waveform seismic facies and depositional facies was established.Thirdly, the control of the ancient valley to depositional facies was characterized by the followings: the south was mainly controlled by down cutting valley, while the northwest and north were mainly by the transfer zone. There were three kinds of the transfer zone in the study area, which controlled the depositional facies at different areas in different forms. Depositional facies was impacted by the fault connect type in the north. Some small fan deltas were controlled by the fault-bend type in the dropping plate of Hengshui Fault. Braided delta was controlled by the fault-cross type in the Nanxiaochenbei area.