Seismic prediction of tide-controlled sand reservoir in Pinghu Formation coal seam, W Gas Field, Xihu Sag, East China Sea Basin

The Xihu Sag in the East China Sea is rich in oil and gas resources and has good exploration and development potential. Pinghu Formation, as an important oil-bearing horizon, has become the focus of exploration and development in the near future. Thin coal seams are widely developed in Pinghu Formation, which leads to multiple solutions of seismic amplitude, phase, and frequency of oil-bearing sand bodies, which seriously restricts the development and production. To identify oil-bearing sandstone under the influence of thin coal seams, reservoir earthquake prediction was carried out. First, the characteristics of tide-controlled sedimentary environment were analyzed in detail through core, well logging, and analytical laboratory data. Then, using rock physical analysis technology, the characteristics of pre-stack collection response of water-bearing sandstone and gas-bearing sand under the influence of thin coal seams were summarized. Finally, the geophysical properties were used to predict the reservoir of tide-controlled sand body, and the favorable target selection in the study area was realized in combination with the sedimentary characteristics. Results show that the Pinghu Formation mainly developed tide-controlled delta-tidal sedimentary environment, in which underwater distributary channel, estuary bar, and tidal sand bar were the dominant sedimentary microfacies. Under the influence of thin coal seam, the sand-body reservoir shows AVO type-Ⅱ response characteristics with wave crest in the short path and trough in the far path. Using prestack gathers response law to guide the P/S velocity ratio inversion, control reservoir quantitative prediction was completed. Based on the understanding of paleo-geomorphology and sedimentary microfacies, the potential of the tidal control environment in the study area could be accurately described, and No.3 sand body is a favorable and potential target. This method improved effectively the accuracy of reservoir prediction in the study area, and provided a technical support for the well location deployment of the deep coal measure tidal control sand body in the block.